Topic 4: Formulas & Names. Equations. Moles-Molar Mass. & Types of Reactions Outline

1. A compound is a substance composed of two or more different elements that are chemically combined in a fixed proportion. A chemical compound can only be broken down by chemical means.

2. Chemical compounds can be represented by a specific formula and assigned a name based on the lUPAC system.

3. Types of chemical formulas include empirical, molecular, and structural. ^ E m p i r i c a l f o r m u l a s s h o w e l e m e n t s in t h e i r s i m p l e s t w h o l e n u m b e r r a t i o s . T h i s m a y o r m a y

n o t b e t h e s a m e a s t h e m o l e c u l a r f o r m u l a . ^ M o l e c u l a r f o r m u l a s s h o w t h e a c t u a l n u m b e r o f a t o m s p e r e l e m e n t in a s i n g l e m o l e c u l e . ^ S t r u c t u r a l f o r m u l a s s h o w t h e n u m b e r o f e a c h t y p e o f a t o m a s w e l l a s t h e i r p h y s i c a l

a r r a n g e m e n t .

4. All chemical reactions show a conservation of mass, energy and charge.

5. A balanced chemical equation represents conservation of atoms.

6. The coefficients in a balanced chemical equation can be used to determine mole ratios in the reaction, and can further be used to predict relationships about amounts between products and reactants.

7. The molar mass of a substance is the sum of the atomic masses of its atoms. The molar mass (gram formula mass) equals the mass of one mole of that substance.

8. The percent composition by mass of each element in a compound can be calculated mathematically.

9. Types of chemical reactions include synthesis, decomposition, single replacement, and double replacement.

25

Equations & Stoichiometrv - Practice Questions

1 . W h i c h s u b s t a n c e h a s t h e g r e a t e s t m o l e c u l a r m a s s ? (1 ) H 2 0 2 ( 2 ) N O ( 3 ) C F , ( 4 ) l 2

2. W h a t is t h e g r a m f o r m u l a m a s s o f C a ( 0 H ) 2 ?

( l ) 2 9 g ( 2 ) 3 4 g ( 3 ) 5 7 g ( 4 ) 7 4 g

3 . W h a t i s t h e t o t a l n u m b e r o f m o l e s o f a t o m s p r e s e n t in 1 g r a m f o r m u l a m a s s o f Pb(C2H302 ) 2 ? ( 1 ) 9 ( 2 ) 1 4 ( 3 ) 3 ( 4 ) 1 5

4 . T h e p e r c e n t by m a s s o f c a r b o n in HC2H3O2 is e q u a l t o

( 1 ) — x l O O ( 2 ) — x l O O ( 3 ) ^ x 1 0 0 ( 4 ) ^ x 1 0 0 ^ ' 6 0 6 0 24 '12

5. W h a t i s t h e e m p i r i c a l f o r m u l a o f C3H6? ( 1 ) C H (2 ) C H 2 ( 3 ) C H 3 ( 4 ) C H 6

6 . T h e n a m e o f t h e c o m p o u n d KCIO2 i s p o t a s s i u m ( 1 ) h y p o c h l o r i t e ( 3 ) c h l o r a t e ( 2 ) c h l o r i t e ( 4 ) p e r c h l o r a t e

7. W h i c h f o r m u l a i s c o r r e c t f o r a m m o n i u m s u l f a t e ? ( l ) N H 4 S 0 i ( 2 ) ( N H , ) 2 S 0 4 ( 3 ) N H , ( S 0 4 ) 2 ( 4 ) ( N H ) 3 ( S O , ) 2

8. T h e m o l e c u l a r f o r m u l a o f a c o m p o u n d i s r e p r e s e n t e d b y X3Y6. W h a t is t h e e m p i r i c a l f o r m u l a o f t h i s c o m p o u n d ? ( 1 ) X 3 Y ( 2 ) X 2 Y ( 3 ) X Y 2 ( 4 ) X Y

9 . T h e n u m b e r o f m o l e s o f m o l e c u l e s i n a 1 2 . 0 - g r a m s a m p l e s o f CI2 Is

( 1 ) — m o l e ( 2 ) — m o l e ( 3 ) 1 2 . 0 m o l e s ( 4 ) 1 2 . 0 x 3 5 . 5 m o l e s 35 .5 71 .0

1 0 . W h a t i s t h e t o t a l n u m b e r o f m o l e s o f s u l f u r a t o m s in 1 m o l e o f F e 2 ( S 0 i ) 3 ? ( 1 ) 1 ( 2 ) 1 5 ( 3 ) 3 ( 4 ) 1 7

1 1 . G i v e n t h e u n b a l a n c e d e q u a t i o n :

CaSOi + AICI3 ^ Al2(S04)3 + CaCb

W h a t is t h e c o e f f i c i e n t o f Al2 (S04)3 w h e n t h e e q u a t i o n Is c o m p l e t e l y b a l a n c e d u s i n g t h e s m a l l e s t w h o l e - n u m b e r c o e f f i c i e n t s ? ( 1 ) 1 (2)2 ( 3 ) 3 ( 4 ) 4

26

1 2 . G i v e n t h e u n b a l a n c e d e q u a t i o n ;

Al (s) + O2 (g) ^ AI2O3 (s)

W h e n t h i s e q u a t i o n i s c o r r e c t l y b a l a n c e d u s i n g s m a l l e s t w h o l e n u m b e r s , w h a t i s t h e c o e f f i c i e n t o f O2 ( g ) ? ( 1 ) 6 (2)2 ( 3 ) 3 ( 4 ) 4

1 3 . G i v e n t h e r e a c t i o n :

4 NH3 + 5 O2 -> 4 NO + 6 H2O

W h a t is t h e to t a l n u m b e r o f m o l e s o f N O p r o d u c e d w h e n 1.0 m o l e o f O2 is c o m p l e t e l y c o n s u m e d ? ( 1 ) 1.0 m o l e ( 2 ) 1.2 m o l e s ( 3 ) 0 . 8 0 m o l e ( 4 ) 4 . 0 m o l e s

1 4 . G i v e n t h e e q u a t i o n :

H2 (g) + CI2 (g) ^ 2 HCI (g)

W h a t is t h e t o t a l n u m b e r o f m o l e s o f HC I ( g ) p r o d u c e d w h e n 3 m o l e s o f H2 ( g ) i s c o m p l e t e l y c o n s u m e d ? ( 1 ) 5 m o l e s ( 2 ) 2 m o l e s ( 3 ) 3 m o l e s ( 4 ) 6 m o l e s

27

Formulas, Equations & Stoichiometry R e v i e w -Cut from Jan 2007 - Jan 2008 Exams

1. W h i c h eq i i a l ion s h o w s conser^'ahoIl o f a toms?

( D l - b + O , ^ 1-1,0 ( 2 ) H , + O2 ^ 2 H2O ( 3 ) 2 H , + O2 2 H , 0 ( 4 ) 2 H2 + 2 O2 -> 2 H2O

2. W h i c h substa j ice c a n be broken d o w n by a chemica l change?

( 1 ) an t imony ( 3 ) hexane ( 2 ) ca rbon ( 4 ) su l fu r

3. What is the g ram f o r m u l a mass o f C a 3 ( P O j ) 2 ? (1) 248 g/mol ( 3 ) 279 g/mol ( 2 ) 263 g/niol ( 4 ) 3 I O g / m o I

4. In w h i c h compound is the ratio o f metal ions to nonmeta l ions 1 to 2^

(1) c a l c i u m b romide ( 2 ) c a l c i u m o x i d e ( 3 ) c a l c i u m phosphide ( 4 ) c a l c i u m su l f i de

5. G i v e n the ba lanced equat ion represent ing a react ion:

2 C O ( g ) + 0 , ( g ) ^ 2 C O , ( g ) What is the mo le rat io o f C C K g ) to C O i C g ) in this reac t ion? (1) 1:1 ( 3 ) 2 : 1

( 2 ) 1:2 ( 4 ) 3 : 2

6. G i v e n the ba lanced equat ion represent ing a react ion:

H* (aq) + O l - r i a q ) ^ 1-1,0(0 + 55 ,8 kJ In this react ion there is conserva t ion o f { 1 ) m a s s , on l y ( 2 ) mass and charge , on l y ( 3 ) mass and energy , o n l y ( 4 ) m a s s , charge , and ene rgy

7. W h i c h po l y a tom i c ion conta ins the greatest number o f o x y g e n a to ins?

( 1 ) acetone ( 3 ) hyd rox ide ( 2 ) ca rbonate ( 4 ) perox ide

8. W h i c h fo rmu la represents an ion ic c o m p o u n d ?

(1) H2 ( 3 ) C H , O H ( 2 ) C H j ( 4 ) N H j C l

9. Wha t is the total number o f d i f fe rent e lements present in N H j N O , ?

(1) 7 ( 3 ) 3 ( 2 ) 9 ( 4 ) 4

10. W h i c h f o rmu la represents lead (11) chromate?

(1) PbCrO . , ( 3 ) P b : C r O j ( 2 ) P b ( C i 0 4 ) , ( 4 ) P b , ( C r 0 4 ) 3

11. W h i c h part ic le d i a g i a m lepresents a samp le o f one c o m p o u n d , on l y ?

K e y

O = a ' o m o f o n e e l e m e n t

= a t o m o f a d i f f e r e n t e l e m e n t

( 1 ) ( 3 )

(2) ( 4 )

28

12. A n atom in the ground slate conta ins a total o f 5 e lectrons, 5 protons, and 5 neutrons. W h i c h L e w i s electron-dot d iagram represents this a tom' '

• X ' • • X * : x :

• • (1) (2) (3) (4)

13. G i v e n the balanced equat ion represent ing the react ion between propane and o x y g e n :

C j H g + 5 0 : -> 3 C O : - 4 H : 0 A c c o r d i n g to this equat ion , w h i c h ratio o f o x y g e n to propane is cor rec t ?

5 grams O,, 10 jjrmns O, 1 gram C.Hj,

5 moles O,, ! mole G.,Hs

( 3 )

(-1)

1J grams Cjll^

10 moles O., I ! moles G.Hg

14. W h i c h substance can be decomposed by chemica l means?

( 1 ) tungsten (3) k rypton ( 2 ) an t imony ( 4 ) methane

15. G i v e n the balanced equat ion represent ing a react ion:

4 N H , + 5 0 , -> 4 N 0 + 6H2O Wha t is the minininni number o f mo les o f O2 that are needed to comple te l y react w i th 16 mo les o f Nl-h? ( 1 ) 1 6 m o l ( 3 ) 6 4 m o l ( 2 ) 20 , mol ( 4 ) 80. mo l

16. E l e m e n t -Vreacts w i th iron to form two di f ferent compounds w i t h the fo rmu las FeA" and Fe iA ' j . T o w h i c h group on the Pe r iod i c T a b l e does e lement ,\ 'belong? ( 1 ) G r o u p 8 ( 3 ) G r o u p 13 ( 2 ) G r o u p 2 ( 4 ) G r o u p 16

17. T h e molar mass o f Ba (OH ) 2 is ( 1 ) 154.3 g ( 3 ) 171.3 g ( 2 ) 155.3 g ( 4 ) 308 . 6 g

18. G i v e n the ba lanced equat ion represent ing a react ion:

1 l2SOj(aq) + 2 K O H ( a q ) -> K 2 S 0 4 ( a q ) + IHiCKI) W h i c h type o f react ion is represented by this equat ion? ( 1 ) decompos i t ion ( 2 ) neutra l izat ion ( 3 ) s ingle replacement ( 4 ) synthes is

19. A hydrated compound conta ins water mo lecu l es w i t h i n i ts c rys ta l s i m c l u r e T h e percent compos i t ion by mass o f water i j i the hydrated compound C a S O j ' 2 H 2 0 has an accepted va lue o f 2 0 . 9 % , A student d id an exper iment and dete rmined that the percent compos i t i on by mass o f w a t e r in C a S O j * 2 H 2 0 was 2 1 . 4 % .

Ca l cu l a t e the percent e r ro r o f the student 's expe i imen ta l result . Y o u r res|X)nse must inc lude hoih a correct numer i ca l setup and the ca lcu la ted result . [ 2 ]

20 . Wr i t e the emp i r i c a l f o m i u l a for the compound CgHig. [ 1 ]

2 9

B a s e y o u r a n s w e r s to q u e s t i o n s 21 t h r o u g h 2 3 o n the i n f o r m a t i o n b e l o w .

S o m e dry c h e m i c a l s can be used to put out forest f i res . One o f these chem i ca l s is N a H C O i . W h e n N a H C O i ( s ) is heated, one o f the products i s C 0 2 ( g ) , as s h o w n in the ba lanced equat ion be low.

2 N a H C O . , ( s ) + heat -> N a j C O j l s ) + H : 0 ( g ) + C 0 2 ( g )

2 1 , S h o w a correct numer i ca l setup for ca l cu l a t i ng the percent compos i t i on by mass o f carbon in the product N a j C O j , [ I J

22 . Ident i fy whether the react ion is endothermic or exo the rm ic , [ I ]

2 3 . De te rm ine the total numbe r o f mo les o f C 0 2 ( g ) produced w h e n 7,0 mo l e s o r N a H C O j ( s ) i s comple te l y reacted, [ 1 ]

mo l e s

24. B a l ance this c h e m i c a l equat ion : [ I ]

S ( s ) + K.CIO. , (s ) S02(g) + K C I ( s ) + energy

B a s e y o u r a n s w e r s to q u e s t i o n s 2 5 t h r o u g h 27 o n the i n f o r m a t i o n be low .

Rus t on an au tomob i l e door conta ins Fe : 0 ,5 ( s ) . T h e ba lanced equat ion represent ing one o f t h e react ions between i ron in the door o f t h e automobi le and o x y g e n in the atmosphere is g i ven be low.

4 F e (s ) + 302 (g) ^ 2Fe20j (s)

2 5 . Ident i fy the type o f c h e m i c a l react ion represented by th is equat ion, [ 1 ]

26, De te rmine the g r a m - f o m n i l a mass o f t h e product o f th is react ion [ 1 ]

27, Wr i t e the l U P A C name for F e203 , [ 1 ]

3 0

B a s e y o u r a n s w e r s to q u e s t i o n s 28 t h r o u g h 3 0 on the i n f o r m a t i o n b e l o w .

Ozone gas, O i , can be used to k i l l adult insects in storage bins for g ra in wi thout da inag ing the gra in . T h e ozone is produced f rom oxygen gas, O ; , in ponable ozone generators located near the storage bins. T h e concentrat ions o f ozone used are so l ow that they do not cause any env i ronmenta l damage. T h i s use o f ozone is sa fer and more env i r onmen ta l l y f r i end ly than a method that used bromomethane , C H j B r . H o w e v e r , bromomethane w a s more e f fec t i ve than ozone because C H j B r k i l l e d immature insects as we l l a s adult insects

Adapted From: TIIL- SiiiKlay (ki:ctle (SchenecLidy. N Y ) 3/9/03

28 . Determine the total number o f moles o f C H 3 B r in 19 g rams o f C H 3 B r ( g ram-fo rmu la mass = 95 granis/n io l ) . [ 1 ]

29 . G i v e n the ba lanced equat ion for produc ing bromomethane :

B r : + C H 4 - > C H j B r + I I B r

Ident i ty the type o f o rgan i c react ion s h o w n . [ I ]

3 0 . B a sed o n the i n fo rmat ion in the passage, state one advantage o f us ing ozone instead o f bromomethane for insect contro l in g r a i n storage bins. [ I ]

3 1

B a s e y o u r a n s w e r s l o q u e s t i o n s 3 1 t h r o u g h 3 3 on the i n f o r m a t i o n b e l o w .

A hydrate is a c om p ound that has water mo lecu l es w i t h i n its cr j 's ta l structure. T h e f o m i u l a for the hydrate C u S 0 4 ' 5 H 2 0 ( s ) s h o w s that there are f i ve mo les o f water for e ve r y one mole o f C u S 0 4 ( s ) . W h e n C u S 0 4 0 H 2 0 ( s ) is heated, the water w i t h i n the c r y s t a l s is re leased, as represented by the ba lanced equat ion be low.

C u S 0 4 - 5 H , 0 ( s ) ^ C u S 0 4 ( s ) + 5 H : 0 ( g )

A student first masses an empty c ruc ib l e ( a heat-resistant conta iner ) . T h e student then masses the c ruc ib l e con ta in ing a s amp le o f C u S 0 j o H 2 0 ( s ) . T h e student repeatedly hea ls and masses the c n i c i b l e and its contents unt i l the mass is constant. T h e s tudent ' s recorded exper imenta l data and ca l cu l a t i ons are s h o w n be low.

D i i t a a n i l c a l c u l a t i o n b e f o r e h e a H i i g :

n ias .s o f C u S O , « . 5 H j O ( s ) atscl c r u c i b l e 2 1 . 3 7 g

- inas.s t i r e n i c i b l e 1 9 . 2 4 i2

m a s s orCiiSO,«5H20{s! 2 . 1 3 g

D a t a a n d c a l c u l a t i o n a i l e r h e a t i n g to a c u n s t u n t muss:

m a s s i)rCuSO|(si a n d c i r u c i b l e 2U.f>l s;

- m a s s o f c r n c i b l e 1 9 . 2 4 a

m: i s s o f O i , S O j ( s > i ..37 o

C a l c u i a l i o n t o d c l e n T i i n e t h e i n a s s oI'M-stter:

mass o f C u S O , « 5 H j O ( s ) 2 . 1 3 g

- m a s s o f C n S O ^ ( s ) 1 ..37 a

m a s s i i f H . 5 0 ( g ) 0 . 7 6 g

3 1 . Ident i fy the total number o f s ign i f i cant figures recorded in the ca l cu la ted mass o f C u S 0 4 * 5 H 2 0 ( s ) . [ I ]

3 2 . In the space below, use the studettt's data to show a correct numerical setup for calculating the [Xjrcent compos i t ion by mass o fwater in the hydrate. [ I j

3 3 . E x p l a i n w h y the samp le in the cn t c ib l e mus t be heated unt i l the constant mass is reached. [ I ]

3 2

TQpi<; $: Bpndinq QMtline

1. Chemical compounds are formed when atoms are bonded together. B r e a k i n g a c h e m i c a l b o n d is a n e n d o t h e r m i c p r o c e s s . F o r m i n g a c h e m i c a l b o n d is a n e x o t h e r m i c p r o c e s s . C o m p o u n d s h a v e l e s s po t en t i a l e n e r g y t h a n t h e i n d i v i d u a l a t o m s t h e y a r e f o r m e d f r o m .

2. Two major categories of compounds are ionic and molecular (covalent) compounds. ^ I o n i c c o m p o u n d s t e n d to b e a m e t a l b o n d i n g w i t h a n o n m e t a l ; o r a m e t a l w i t h a p o l y a t o m i c

i on M o l e c u l a r ( c o v a l e n t ) c o m p o u n d s t e n d t o b e t w o o r m o r e n o n m e t a l s c o m b i n e d .

3. Compounds can be differentiated by their chemical and physical properties. I o n i c s u b s t a n c e s h a v e h i g h m e l t i n g a n d bo i l i ng p o i n t s , f o r m c r y s t a l s , d i s s o l v e in w a t e r ( d i s s o c i a t e ) , a n d c o n d u c t e l e c t r i c i t y in s o l u t i o n a n d a s l i q u i d s .

^ C o v a l e n t o r m o l e c u l a r s u b s t a n c e s h a v e l o w e r m e l t i n g a n d bo i l i ng p o i n t s , d o n o t c o n d u r t e l e c t r i c i t / .

4. Atoms gain a stable electron configuration by bonding with other atoms. A t o m s a r e s t a b l e w h e n t h e y h a v e a fu l l v a l e n c e l e v e l . M o s t a t o m s n e e d 8 e l e c t r o n s t o fill t h e i r v a l e n c e l e v e l .

^ H a n d H e o n l y n e e d 2 e l e c t r o n s to fill t h e i r v a l e n c e l e v e l . T h e n o b l e g a s e s ( g r o u p 1 8 ) h a v e f i l l ed v a l e n c e l e v e l s . T h e y d o n o t n o r m a l l y b o n d w i t h o t h e r a t o m s .

5. Chemical bonds are formed when valence electrons are: ^ T r a n s f e r r e d f r o m o n e a t o m to a n o t h e r - i on i c .

S h a r e d b e t w e e n a t o m s - c o v a l e n t . Mob i l e In a f r e e m o v i n g " s e a " o f e l e c t r o n s - m e t a l l i c .

6. In multiple (double or triple) covalent bonds more than 1 pair of electrons are shared between two atoms.

o x y g e n a n d i t ' s f a m i l y ( g r o u p 1 6 ) f o r m d o u b l e b o n d s w i t h e a c h o t h e r (O2)

^ n i t r o g e n a n d i t ' s f a m i l y ( g r o u p 1 5 ) f o r m t r i p l e b o n d s w i t h e a c h o t h e r (NH3) c a r b o n c a n f o r m d o u b l e a n d t r i p l e b o n d s w i t h i t s e l f & g r o u p 1 6 a n d 1 5 e l e m e n t s ( e x : CO2)

3 3

7. Polarity of a molecule can be determined by its shape and the distribution ofthe charge. ^ P o l a r m o l e c u l e s h a v e a n a s y m m e t r i c a l ( u n e v e n ) d i s t r i b u t i o n o f e l e c t r o n s in t h e m . ^ A s a r e s u l t , p o l a r m o l e c u l e s h a v e ( + ) a n d (-) c h a r g e d e n d s . ^ W a t e r is t h e m o s t c o m m o n s u b s t a n c e c o m p o s e d o f p o l a r m o l e c u l e s ; 0 e n d is (- ) , H e n d s a r e

( + ) • ^ N o n p o l a r m o l e c u l e s h a v e s y m m e t r i c a l ( e v e n ) d i s t r i b u t i o n o f e l e c t r o n s i n t h e m . ^ P o l a r s u b s t a n c e s a r e d i s s o l v e d o n l y b y a n o t h e r p o l a r s u b s t a n c e . N on-p o l a r s u b s t a n c e s a r e

d i s s o l v e d o n l y b y o t h e r n o n - p o l a r s u b s t a n c e s .

8. The electronegativity difference between two bonded atoms can determine the type of bond and its polarity. 0 . 0 = n o n - p o l a r c o v a l e n t 0 . 0 - 1 . 7 = po l a r c o v a l e n t 1 . 7 + = i o n i c

9. Bonding guidelines: M e t a l s r e a c t w i t h n o n m e t a l s to f o r m ion i c c o m p o u n d s .

^ N o n m e t a l s b o n d w i t h n o n m e t a l s to f o r m c o v a l e n t c o m p o u n d s ( m o l e c u l e s ) . ^ I o n i c c o m p o u n d s w i t h p o l y a t o m i c i o n s h a v e b o t h i o n i c a n d c o v a l e n t b o n d s .

10. Intermolecular forces allow different particles to be attracted to each other to form solids and liquids. ^ H y d r o g e n b o n d s a r e a n e x a m p l e o f a s t r o n g I M F b e t w e e n p o l a r m o l e c u l e s . ^ H y d r o g e n b o n d s e x i s t b e t w e e n a t o m s o f h y d r o g e n o n o n e m o l e c u l e a n d a t o m s o f e i t h e r

o x y g e n , f l u o r i n e , o r n i t r o g e n o n a n e i g h b o r i n g m o l e c u l e . S u b s t a n c e s w i t h h y d r o g e n b o n d s t e n d t o h a v e m u c h h i g h e r m e l t i n g a n d bo i l i ng p o i n t s t h a n t h o s e w i t h o u t h y d r o g e n b o n d s . W a t e r i s o n e s u c h s u b s t a n c e O r d i n a r y p o l a r m o l e c u l e s s i m p l y a t t r a c t e a c h o t h e r a s t h e i r o p p o s i t e l y c h a r g e d e n d s l i n e u p .

^ N o n p o l a r m o l e c u l e s u s e w e a k V a n d e r W a a l ' s f o r c e s o f a t t r a c t i o n a n d a s a r e s u l t t e n d t o h a v e l o w e r m e l t i n g p o i n t s , a n d h i g h e r v a p o r p r e s s u r e s .

11. Metallic bonding occurs between atoms of metal. The valence electrons are loosely held by all atoms in a mobile "sea" of valence electrons. ^ T h i s t y p e o f b o n d i n g a c c o u n t s fo r s o m e o f t h e u n i q u e p r o p e r t i e s o f m e t a l s , s u c h a s t h e i r

ab i l i t y t o c o n d u c t e l e c t r i c i t y , l u s t e r , a n d m a l l e a b i l i t y .

12. Physical properties of a substance can be explained in terms of chemical bonds and intermolecular forces. These include conductivity, malleability, solubility, ductility, hardness, melting point and boiling point, vapor pressure.

3 4

Bondino - Practice Questions

1 . T h e f o r c e s b e t w e e n a t o m s t h a t c r e a t e c h e m i c a l b o n d s a r e t h e r e s u l t of i n t e r a c t i o n s b e t w e e n ( 1 ) n u c l e i ( 3 ) p r o t o n s a n d e l e c t r o n s ( 2 ) e l e c t r o n s ( 4 ) p r o t o n s a n d n u c l e i

2 . A c c o r d i n g t o R e f e r e n c e T a b l e S , w h i c h s e q u e n c e c o r r e c d y p l a c e s t h e e l e m e n t s in o r d e r o f i n c r e a s i n g i on i za t i on e n e r g y ? ( 1 ) H Li - ) N a ^ K ( 3 ) 0 ^ S S e ^ T e ( 2 ) I B r ^ C I -» F ( 4 ) H ^ B e -> A l ^ G a

3 . E l e c t r o n e g a t i v i t / i s a m e a s u r e o f a n a t o m ' s ab i l i t y t o ( 1 ) a t t r a c t t h e e l e c t r o n s in t h e b o n d b e t w e e n t h e a t o m a n d a n o t h e r a t o m ( 2 ) r e p e l t h e e l e c t r o n s in t h e b o n d b e t w e e n t h e a t o m a n d a n o t h e r a t o m ( 3 ) a t t r a c t t h e p r o t o n s o f a n o t h e r a t o m ( 4 ) r e p e l t h e p r o t o n s o f a n o t h e r a t o m

4 . If t h e e l e c t r o n e g a t i v i t y d i f f e r e n c e b e t w e e n t h e e l e m e n t s in c o m p o u n d N a X i s 2 . 0 , w h a t i s e l e m e n t X ? ( 1 ) b r o m i n e ( 2 ) c h l o r i n e ( 3 ) f l u o r i n e ( 4 ) o x y g e n

5. A n e l e m e n t w i t h a n e l e c t r o n e g a t i v i t / o f 0 . 9 b o n d s w i t h a n e l e m e n t w i t h a n e l e c t r o n e g a t i v i t y o f 3 . 1 . W h i c h p h r a s e b e s t d e s c r i b e s t h e b o n d b e t w e e n t h e s e e l e m e n t s ?

( 1 ) m o s t l y ion ic in c h a r a c t e r a n d f o r m e d b e t w e e n t w o n o n m e t a l s ( 2 ) m o s t l y i on i c in c h a r a c t e r a n d f o r m e d b e t w e e n a m e t a l a n d a n o n m e t a l ( 3 ) m o s t l y c o v a l e n t in c h a r a c t e r a n d f o r m e d b e t w e e n t w o n o n m e t a l s ( 4 ) m o s t l y c o v a l e n t in c h a r a c t e r a n d f o r m e d b e t w e e n a m e t a l a n d a n o n m e t a l

6 . W h i c h t y p e o f b o n d e x i s t s b e t w e e n a n a t o m o f c a r b o n a n d a n a t o m o f f l u o r i n e ? ( 1 ) i o n i c ( 2 ) m e t a l l i c ( 3 ) p o l a r c o v a l e n t ( 4 ) n o n p o l a r c o v a l e n t

7. W h i c h p a i r o f a t o m s i s h e l d t o g e t h e r by a c o v a l e n t b o n d ? ( l ) H C I ( 2 ) L i C I ( 3 ) N a C I ( 4 ) K C I

8 . W h i c h s u b s t a n c e c o n t a i n s n o n p o l a r c o v a l e n t b o n d s ? ( 1 ) H 2 ( 2 ) H 2 0 ( 3 ) C a ( O H ) 2 ( 4 ) C a O

9 . G i v e n t h e r e a c t i o n : CI (g) + CI (g)-> CI2 (g) + energy W h i c h s t a t e m e n t b e s t d e s c r i b e s t h e r e a r t i o n ?

( 1 ) A b o n d is f o r m e d a n d e n e r g y i s a b s o r b e d . ( 2 ) A b o n d is f o r m e d a n d e n e r g y i s r e l e a s e d . ( 3 ) A b o n d is b r o k e n a n d e n e r g y i s a b s o r b e d . ( 4 ) A b o n d is b r o k e n a n d e n e r g y i s r e l e a s e d .

1 0 . T h e p r i m a r y f o r c e s o f a t t r a c t i o n b e t w e e n w a t e r m o l e c u l e s in H2O ( I ) a r e ( 1 ) i o n i c b o n d s ( 3 ) m o l e c u l e - i o n a t t r a c t i o n s ( 2 ) h y d r o g e n b o n d s ( 4 ) v a n d e r W a a l s f o r c e s

35

1 1 . Which structure represents a polar molecule?

( l ) H - H ( 3 )

( 2 ) H - C = C - H ( 4 ) . . n — u V

1 2 . W h i c h e l e c t r o n d o t d i a g r a m r e p r e s e n t s a m o l e c u l e t h a t h a s a po l a r c o v a l e n t b o n d ?

1) : F : M g : F :

2)

3)

4)

: C l : C i : • • • •

: N = N :

H - N - H

I H

3 6

Bonding Review - Cut from Jan 2007 - Jan 2008 Exams

1. G i ven the balanced equation:

I + I ^ l2 Which statement describes the process represented by this equation? ( 1 ) A bond is fonned as energy is absorbed. ( 2 ) A bond is fonned and energy is released. ( 3 ) A bond is broken as energy is absorbed. (4 ) A bond is broken and energy is released.

2 . A n o.xygen molecule contains a double bond because the two atoms o f oxygen share a lota! o f

( 1 ) 1 electron ( 3 ) 3 electrons ( 2 ) 2 electrons ( 4 ) 4 electrons

3. A double carbon-carbon bond is found in a molecule o f

( 1 ) pentane ( 3 ) pent>'ne ( 2 ) pentene ( 4 ) pentanol

4. At S T P , fluorine is a gas and bromine is a l iquid because, compared to fluorine, bromine has

( 1 ) stronger covalent bonds ( 2 ) stronger intennolecular forces ( 3 ) weaker covalent bonds ( 4 ) weaker intennolecular forces

5. Wh i ch t cnn indicates how strongly an atom attracts the electrons in a chemica l bond?

( 1 ) alkalinit>' ( 2 ) atomic mass ( 3 ) e lectronegativity ( 4 ) act ivat ion energy

6. Magnes ium nitrate contains chemica l bonds that are

( 1 ) covalent , on ly ( 2 ) ionic , only ( 3 ) both covalent and ionic ( 4 ) neither covalent nor ionic

7. A sol id substance Is an excef lent conductor o f electricit>'. T h e chemica l bonds in this substance are most l i ke l y ( 1 ) ion ic , because the va lence electrons are shared between atoms ( 2 ) ion ic , because the \e electrons are mobile ( 3 ) meta l l i c , because the va lence electrons are stationary ( 4 ) meta l l i c , because the va lence electrons are mobile

8- When sodium and fluorine combine to produce the compound NaF . the ions formed ha\ the same electron configurat ion as atoms o f

( 1 ) argon, only ( 2 ) neon, only ( 3 ) both argon and neon ( 4 ) neither argon nor neon

9. A toms o f wh ich element have the greatest tendency to gain electrons?

( 1 ) bromine (3 ) fluorine ( 2 ) chlor ine ( 4 ) iodine

1 0 . Wh i ch polyatomic ion contains the greatest number o f oxygen atoms?

( 1 ) acetate ( 3 ) hydroxide ( 2 ) carbonate ( 4 ) peroxide

1 1 . Wh i ch fomiu la represents an ionic compound? ( 1 ) H2 ( 3 ) C H . i O H ( 2 ) C H J { 4 ) N H 4 C 1

1 2 . Wh i ch l iquid has the highest vapor pressure al 7 5 X ?

( 1 ) ethanoic acid ( 3 ) propanone ( 2 ) eihanol ( 4 ) water

1 3 . G i v e n the balanced equation representing a reaction:

C l 2 ( g ) - a ( g ) + C l ( g ) What occurs during this change? ( 1 ) Energ> is absorbed and a bond is broken. ( 2 ) Energy is absorbed and a bond is formed. ( 3 ) Energy is released and a bond is broken. ( 4 ) Energy is released and a bond is fonned.

14. A l standard pressure, a certain compound has a low boi l ing point and is insoluble in water. A l S T P , this compound most l ike ly exists as

( 1 ) ionic cr>stals ( 2 ) metal l ic cr>'stals ( 3 ) nonpolar molecules ( 4 ) polar molecules

3 7

1 5 . W h i c h group on ihe Per iodic Tab le o f the E lements contains elements that react wi th oxygen to form compounds wi th the general formula A'20?

( 1 ) Group 1 ( 3 ) Group 14 ( 2 ) G roup 2 ( 4 ) Group 18

1 6 . Wh i ch two substances are covalent compounds? ( 1 ) C 6 H i 2 0 6 ( s ) a n d K l ( s ) ( 2 ) C 6 H i 2 0 6 ( s ) a n d H C l ( g ) ( 3 ) K I ( s ) a n d N a C ! ( s ) ( 4 ) N a C I ( s ) and H C l ( g )

1 7 . Wh i ch compound has hydrogen bonding between its molecules?

( 1 ) C H 4 { 3 ) K H ( 2 ) CaH2 ( 4 ) N H 3

18. Wh i ch L e w i s electron-dot diagram conec t l y represents a hydrox ide ion?

: 0 : H : 0 : : H

( 1 ) { 3 )

: 0 : H : ' " : 0 : H :

( 2 ) ( 4 )

19. Exp l a i n , in terms o f electronegativity, why a P-CI bond m a molecule o f PCI5 is more polar than a P-S bond in a molecule o f P : S5 . [ I ]

Base your answers to questions 20 and 21 on the infonnat ion below.

The graph below shows the relationship between boi l ing point and molar mass at standard pressure for pentane, hexane, heptane, and nonane.

160.

140.

p 120.

I 100.

B o i l i n g P o i n t V e r s u s Mo la r M a s s of S o m e A l k a n e s

i r > [

\ 1 !

< j 1 1

7 3 . 80. te: lOO, 110,

Molar Mass (gr'tolj

20, 130,

20. Octane has a molar mass o f 114 grams per mole. Accord ing to this graph, what is the boi l ing point o f octane at standard pressure? 11 ]

2 1 . State the relat ionship between molar mass and the strength o f intemiolecular forces for the selected alkanes. | i |

3 9

Base your answers to quest ions 22 through 24 on the in fonnat ion below.

T h e particle diagrams below represent the react ion between two nonmetals. A2 and O2.

Key Atom of element .4

0 = Atom d element Q

R e a c t a n t s P r o d u c t

22 . Us ing the symbo ls A and O , wr i te the chemica l fonnu la o f t he product, [ l ]

23 . Identify the t\'pe o f chemica l bond between an atom o f element A and an atom o fe l ement O. [ l ]

24. Compare the total mass o f t he reactants to the total mass o f the product, [ l ]

25. E x p l a i n , in terms o f molecu lar stnicture or distr ibut ion o f charge, why a molecule o f methane is nonpolar. [1]

26. A l iquid boi ls when the vapor pressure o f t he l iqu id equals the atmospheric pressure on the surface o f t he l iqu id . Us ing Reference Tab le H. detemiine the boi l ing point o f water when the atmospheric pressure is 90. k P a . ( I ]

4 0

Base your answers to questions 2 7 through 3 0 on the infonnat ion below.

Have you ever seen an insect ca l led a water strider " s k a t i n g " across the surface o f a cahn pond? Have you ever " f l o a t ed " a sewing needle on the water in a glass? I f y o u have, then you ' ve obser\ed one o f water ' s many amaz ing properties. Water 's surface tension keeps the water strider and the sewing needle from s ink ing into the water. S imp ly stated, the surface tension is due to the forces that hold the water molecules together. Without these intennolecular forces, Ihe water strider and the sewing needle wou ld sink below the surface o f the water. T h e surface tension o f water at var ious temperatures is g iven in the data table below.

Sortace Tension at Different Water Temperatures

Water Tatnperature r c )

Surface Tension

lU. 74.2 25 72,0 50. 67.9 75 Go,6

too. 58.9

27 . On a piece o f grapli paper, plot tlie data from tlic data table. C i r c l e and connect the five points, [ l ]

28. Accord ing to your graph, wliat is the surface tension o f w a t e r at 60. °C? [ l ] mN/in

29. State the relationship between the surface tension and the temperature o fwa t e r . [ I ]

3 0 . The surface tension of l iqu id tetrachloromethane. C C I J , at 2 5 ° C is 2 6 . 3 mi l l inewlons/ meter (mN/ni ) . Compare the in lennolecu lar forces between molecules o f C C l j lo the intemiolecular forces between molecules o fwa t e r , H : 0 . at 2 5 ° C . [ I ]

4 1

Topic 6 Overview

Topic 6A: Heat & Temperature 1. Energy can exist in different forms - chemical, electrical, electromagnetic, thermal, mechanical, nuclear.

S t o r e d e n e r g y i s r e f e r r e d to a s p o t e n t i a l energy. E n e r g y o f m o t i o n i s k i n e t i c e n e r g y .

2. The Law of Conservation of Energy states that energy can not be lost or destroyed, only changed from one form to another.

3. Heat is a transfer of energy (often but not always thermal energy) from a body of higher temperature to a body of lower temperature.

4. Temperature is a measure of the average kinetic energy of the particles in a sample. Temperature is NOT a form of energy and should not be confused with heat.

5. The concepts of kinetic and potential energy can be used to explain physical processes such as fusion (melting), solidification (freezing), vaporization (boiling, evaporation), condensation, sublimation, and deposition.

6. Processes that are exothermic give off heat energy. This typically causes the surrounding environment to become warmer.

7. Processes that are endothermic absorb energy. This typically causes the surrounding environment to become colder.

4 2

Topic 6A: Heat &Tgmpgral;ure Outline

1. Temperature is a "measure of the average kinetic energy of the particles in a sample of matter."

Kinetic energy is energy due to motion. So as temperature increases, the particles move faster, on average. Temperature does NOT depend on the mass ofthe sample.

2. Temperature scales used by chemists are the Celsius and Kelvin scales. The freezing point of water is a reference point often used in science, and is referred to as "standard temperature." Its value is 0°C or 273 K, and is noted on Table A.

^ The boiling point of water is 100°C or 373 K. Converting from C° to K: K = C° + 273 (on Table T)

3. Heat is a form of energy and IS NOT the same as temperature. ^ Heat is dependent on mass. There is more heat in an iceberg that is at O C than a cup

full of boiling water. Heat can be transferred from one substance to another when their particles are in contact (when the objects touch). Heat will move from the object with more particle KE (higher temp) to the one with less. The amount of heat needed to cause a temperature change is dependent on the mass of the sample, its "specific heat" and the amount of temperature change: q = m c AT (Table T) When heat is absorbed to cause a temperature change, it is resulting in a change in KE of particles. The amount of heat needed to cause a phase change can be calculated using the q = mHf (melting), or q = mHv (boiling) (Table T). When heat is added to cause a phase change, it is causing a change in intermolecular forces between particles. The values for water are on Table B.

4. Heat of fusion (Hf) is the energy needed to convert one gram of a substance from solid to liquid.

5. Heat of vaporization (H,) is the energy needed to convert one gram of a substance from liquid to gas.

6. Specific heat (C) is the energy required to raise one gram of a substance 1 degree (Celcius or Kelvin).

The specific heat of liquid water is 1 cal/g*J or 4.2 J/g*K.

43

7. The three phases of matter are solid, liquid and gas. Each has its own properties. ^ Solids have a constant volume and shape. Particles are held in a rigid, cr/stalline strurture. ^ Liquids have a constant volume but a changing shape. Particles are mobile but still held

together by strong attraction. ^ Gases have no set volume or shape. They will completely fill any closed contained. Particles

have largely broken free of the forces holding them together. ^ The phase a substance is in is dependent on the temperature. Melting points and boiling

points are on Table S (in Kelvin degrees).

8. Phase changes are a type of physical change. If they are changes that involve heat being absorbed, they are endothermic changes.

^ Endothermic phase changes are melting, boiling, evaporating and subliming (s->l). ^ Opposite type of phase changes (freezing, condensing, depositing) are exothermic.

9. A heating curve (or cooling curve) traces the changes in temperature of a substance as it changes from solid to liquid to gas (or gas to liquid to solid). ^ When the substance undergoes a phase change, there is no change in temperature. The line

"flattens" until the phase change is complete. When a phase change is occurring, the potential energy of the substance changes while kinetic energy remains the same.

^ As temperature increases, kinetic energy increases.

10. The amount of heat involved in some chemical changes is shown on Table I, called "heat of reaction" or AH.

^ If the value is negative, the reaction is exothermic. ^ This can be expressed as a potential energy diagram. ^ If the energy is written into the equation, and is on the reactants side, the reaction is

endothermic. ^ AH is the difference between the energy stored in the products (PE) and the potential

energy of the reactants.

11. Breaking bonds is ALWAYS endothermic, and forming bonds is ALWAYS exothermic.

< I + I I2 Bond is forming, I atoms are become stable by bonding, so they release energy (Exo) H2 H + H Bond is breaking, requires energy in order to put atoms in unbonded state (endo)

44

Heat and Temperature - Cut from Jan 2007 - Jan 2008 Exams

1. G i v e n the balanced equation: 1 ^ I — l2

Wh i ch slateii ieni descnbes the process represented by this equation? ( 1 ) A bond is formed as energy is absorbed. ( 2 ) A bond is fonned and energy is released. (3) A bond is broken as energy is absorbed. ( 4 ) A bond is broken and energy is released.

2. W h i c h term is def ined as a measure o f the average kinet ic energ\ o f t h e pan ic les in a sample?

( 1 ) temperature ( 3 ) thennal energy ( 2 ) pressure ( 4 ) chemica l energ>'

3. Wh i ch tenn refers to the dilTerence between the potential energy o f the products and the potential energy o f t h e reactants for any chemica l change? ( t ) heat o f deposition ( 2 ) heat o f fusion (3) heat o f reaction ( 4 ) heat o f vaporization

4. W h i c h ke lv in temperature is equal to 56°C? ( 0 - 3 2 9 K ( 3 ) 2 1 7 K ( 2 ) - 2 ! 7 K ( 4 ) 3 2 9 K

5. Wh i ch reaction releases the greatest amount o f energy per 2 moles o f product? ( 1 ) 2 C O ( g ) + 0 : ( g ) - 2 C 0 2 ( g ) ( 2 ) 4 A l ( s ) + 302 (g ) — 2 A l 2 0 3 ( s ) (3) 2H2(g) + 0 2 ( g ) - 2 H 2 0 ( g ) ( 4 ) N2(g) + 3 H 2 ( g ) - 2 N H 3 ( g )

Use the reaction shown below to answer questions 6 and 7.

GgDj ig i * oO,i j : . ) ^ 3 C O , i g i 4- 4H^)i.Ci + 221.9.2 kJ

6. D raw a potential energy d iagram for this reaction. [ I ]

7. Determine the total amount o f energy released when 2.50 moles o f propane is completely reacted w i th oxygen. [1]

45

8. G i v e n the balanced equation representing a reaction; N2(g) + 0 2 ( g ) + 182.6 kJ —• 2 N 0 ( g ) D r a w a potential energ>' d iagram for this react ion. | i |

Base your answers to questions 9 through 11 on the informat ion below.

A 5.00-gram sample o f l iqu id ammon ia is or ig inal ly at 210. K. T h e diagram o f the partial heating curve below represents the vapor izat ion o f the sample o f ammonia at standard pressure due to the addition o f heat. T h e heal is no/ added at a constant rate.

Part ia l Heat ing C u r v e for A m m o n i a

A B C D

Some physica l constants for ammon ia are shown in the data table below. Some Physical Constants lor Ammonia

s p e c i f t ; h e a t c a p a c i t y of HH^i\ 4 71 J g - K

h e a t or tus i on

h e a t of v a p o f f z a t i o n 1 3 7 0 J ' ' 9

9. Ca lcu la te the total heat absorbed by the 5.00-gram sample o f ammon ia dur ing time i n t ena l AfS. Y o u r response must include horh a correct numer ica l setup and the calculated result. [2 ]

10. Descr ibe what is happening to hoih the potential energy and the average k inet ic enei^y o f t h e molecu les in the ammonia sample during time i n t e n a l BC'. Y o u r response must include hoih potential energy and average kinet ic energy. [ I ]

11. Determine the total amount o f heat required to vaporize this 5.00-gram sample o f ammonia at its boi l ing point. [1 ]

46

Base your answers to quest ions 12 through 14 on the information below.

A 100.0-gram sample o f N a C l ( s ) has an ini t ia l temperature o f O X . A chemist measures the temperature o f the sample as it is heated. Heat is noi added at a constant rate. T h e heating curxe for the sample is shown below.

Heating C u r v e for Sod ium Ch lo r i de

T i m e

12, Determine the temperature range over w h i c h the entire NaC I sample is a l iquid. j i |

13. Identify one l ine segment on the cur\'e where the average k inet ic energy o f t he particles o f t h e N a C l sample is changing. 11|

14. Identify one l ine segment on the curve where the NaC l sample is in a single phase and capable o f conducting electr icity. 111

47

Base your answers to questions I 5 and 16 on the infonnat ion below,

A student performed an exper iment lo determine the total amount o f energy stored in a peanut. T h e accepted value for the energy content o f a peanut is 30.2 k i lo joules per gram. T h e student measured 100.0 grams o f water into a metal can and placed the can on a ring stand, as shown in the diagram below. T h e peanut was attached to a w i re suspended under the can. T h e ini t ia l temperature o f the water w a s recorded as 2 2 . O X . T h e peanut was ignited and a l lowed to burn. When the peanut finished burning, the final water temperature was recorded as 57.0°C. T h e student's exper imenta l value for the energy content o f this peanut was 25 .9 k i lo joules per gram,

p The rmometer

•Metal can

•Peanut

15, Ca lcu la te the total amount o f heal absorbed by the water. Y o u r response must include bofit a correct numerica l setup and the calculated result. |2|

16. Detennine the student's percent error for the energ\ content o f this peanut. | 1 |

48

Base your answers lo questions 17 through 20 on the infonnat ion below.

T h e temperature o f a sample o f a substance is increased trom 20.°C to 160.°C as the sample absorbs heat at a constant rate o f 15 ki lo joules per minute at standard pressure. T h e graph below represents the relationship between temperature and time as the sample is healed

T e m p e r a t u r e V e r s u s T i m e

180. -, 1 ' , r-

0 2,0 4,0 6.0 8,0 10.0 12,0 T i m e (rnin)

17, What is the boi l ing point o f this sample? [ l ]

18, D r a w ut least nine particles in the box, showing the correct particle arrangement o f this sample during the first minute o f heating, [ l ]

19. What is the total time this sample is in the l iquid phase, only? [ I ]

20. Determine the total amount o f heat required to complete ly melt this sample al its melting point, [ l ]

49

Topic 6B: Reaction Rate & Equilibrium Outline

1. Collision theory states that a reaction is most likely to occur if reactant particles collide with the proper energy and orientation.

T h i s is s o m e t i m e s ca l led an " e f f ec t i ve co l l i s ion . "

2. The rate of a chemical reaction depends on temperature, concentration, nature of the reactants, surface area and the presence of a catalyst.

3. Energy absorbed or released by a chemical reaction can be represented by a potential energy diagram.

4. The amount of energy released or absorbed during a chemical reaction is the heat of reaction.

Hea t o f react ion equa l s the P E of the products - PE of r eac t an t s . Pos i t ive hea t o f react ion impl ies a n end o the rm i c react ion . Negat ive heat of react ion impl ies a n ex o the rm i c react ion .

5. A catalyst provides an alternative pathway for a chemical reaction. The catalyst lowers reaction the activation energy required to start up the reaction.

Adding a ca ta l ys t i n c r ea ses the ra te of the fomia rd and r e v e r s e r e a a i o n s equa l l y , so there is no sh i f t in equ i l ib r ium. Know how the use of a ca ta l ys t a f f ec t s the P E d i ag r am.

6. Entropy is a measure of the randomness or disorder in a system. A system with greater disorder has greater entropy.

7. Systems in nature tend to undergo changes towards lower energy (tend to be exothermic) and higher entropy.

8. At equilibrium the rate of the forward reaction equals the rate of the reverse reaction.

T h i s s ta te can only be a c h i e v e d I F the s y s t e m ( con t a i ne r ) is c l osed a n d the condit ions o f T e m p and P ressu re a re held s teady .

9. The measurable quantities of reactants and products remain constant at equilibrium.

T h i s does NOT m e a n t he a m o u n t s o f p rod u r t s and r e a c t a n t s is the s a m e as each other , but ra the r that the a m o u n t s a r e no longer chang ing .

10. Types of equilibrium include chemical, phase and solution. So lut ions that a r e s a t u r a t e d r ep resen t an equi l ibr ium b e t w e e n the p r o c e s s e s of d isso lv ing a n d precipi tat ing.

^ A n e x a m p l e of a phase equ i l ib r ium wou ld be the s i m u l t a n e o u s me l t i ng and f reez ing of wa t e r if the s y s t e m is held a t O'C.

11. LeChatelier's principle can be used to predict the effect of stress on a system in equilibrium.

S t r e s s e s include a c h a n g e in p r e s s u r e , v o l u m e , concen t r a t i on , a n d t e m p e r a t u r e .

Y o u shou ld be able to predic t if a " s h i f t l e f t " or a " s h i f t r i g h t " o c c u r s due to a part icular s t r e s s .

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Rate of Reaction & Equil ibrium -Cut from Jan 2007 - Jan 2008 Exams

1. G i v e n the equation representing a phase change al equihbr ium:

VVliich statement is true? ( 1 ) T h e forward process proceeds faster than the reverse process. ( 2 ) T h e reverse process proceeds faster than the forward process. ( 3 ) T h e forward and reverse processes proceed at the same rate. ( 4 ) T l i e forward and reverse processes both stop.

2. A 5.0-gram sample o f zinc and a 50.-milHhier sample o fhyd roch lo r i c ac id are used in a chemica l reaction. Wh i ch combinat ion o f these samples has the fastest reaction rale? ( 1 ) a z inc strip and 1.0 M H C I { a q ) ( 2 ) a z i nc strip and 3.0 M H C I { a q ) ( 3 ) z inc powder and 1.0 M H C I ( a q ) ( 4 ) z inc powder and 3.0 M H C I ( a q )

3. Fo r a g i\n react ion, adding a catalyst increases the rate o f the reaction by ( 1 ) prov id ing an alternate reaction pathway that has a higher act i\a l ion energy ( 2 ) prov id ing an alternate reaction pathway that has a lower act ivat ion energy ( 3 ) us ing the same reaction pathway and increas ing the act i\at ion energy ( 4 ) using the same reaction pathway and decreasing the act ivat ion energy

4. G i v e n the equation representing a reaction at equ i l ib r ium:

W h i c h change causes the equi l ibr ium lo shift to the right? ( 1 ) decreas ing the concentrat ion o f H2(g) ( 2 ) decreasing the pressure ( 3 ) increasing the concentrat ion o r N : ( g ) ( 4 ) increas ing the temperature

5. G i v e n the equation representing a system at equ i l ibr ium:

At w h i c h temperature does this equi l ibr ium exist al 101.3 k i lopascals?

{ 1 ) 0 K ( 3 ) 3 2 K ( 2 ) O X ( 4 ) 2 7 3 T

6. Wh i ch stalement must be tiiie when solution equi l ibr ium occurs? ( 1 ) T h e solution is at S T P . ( 2 ) T l i e solution is supersaturated. ( 3 ) T l i e concentration o f the solution remains constant. ( 4 ) T h e masses o f the d isso lved solute and the undissolved solute are equal.

7. Wh i ch statement must be tnie for any chemica l reaction at equi l ibr ium? ( 1 ) T l i e concentration o f t he products is greater than the concentration o f the reactants. ( 2 ) T h e concentration o f the products is less than the concentration o f the reactants. ( 3 ) T h e concentration o f t he products and the concentration o f the reactants are equal. (4 ) T l i e concentration o f the products and the concentration o f the reactants are constant.

8. G i v e n the balanced equation representing a reaction at 101.3 kPa and 298 K:

+ mj.ii^ -Ni-uig) + 91,8 kj Wh i ch stalement is tnie about this reaction? ( 1 ) It is exothermic and ®H equa l s-91 .8 k J . ( 2 ) It is exothermic and ®//equals +91.8 k J . ( 3 ) It i s endo lhenn i c and 0H equa l s-91 .8 k J . ( 4 ) It i s endolhennic and QH equals +91.8 k J .

9. Wh i ch balanced equation represents a phase

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equ i l ib r ium?

10. G i v e n the system at equ i l ib r ium:

Wh i ch changes occur when 0 2 ( g ) is added to this system? ( 1 ) T h e equi l ibr ium shifts to the right and the concentration o f PC l3 (g ) increases. ( 2 ) T h e equi l ibr ium shifts to the right and the concentration o f P C b ( g ) decreases. ( 3 ) T h e equi l ibr ium shifts to the left and the concentrat ion o f PC l3 (g ) increases. ( 4 ) T h e equ i l ib r ium shifts to the left and the concentrat ion o f PC l3 {g ) decreases.

12. E x p l a i n , in terms o f co l l i s ion theor\', w h y the rate o f a chemica l reaction increases wi th an increase in temperature. [ I J

Base your answers to quest ions 13 through 15 on the informat ion below.

A beaker contains 100.0 mi l l i l i t e rs o f a dilute aqueous solution o f ethanoic ac id at equi l ibr ium. The equation below represents this system.

13. Compare the rate o f the forward reaction to the rate o f the reverse reaction for this sys tem. | i l

14. Descr ibe what happens to the concentrat ion o f H+(aq) when 10 drops o f concentrated H C 2 H i 0 2 ( a q ) are added to this sys tem. | l l

15. D r a w a structural fonnu la for ethanoic ac id . \

I I . In tenns o f energy and entropy, systems in nature tend to undergo changes toward ( 1 ) higher energy and higher entropy ( 2 ) higher energy and lower entropy ( 3 ) lower energ>' and higher entropy ( 4 ) lower energy and lower entropy

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Base your answer to question 16 on the infonnat ion below.

" H a n d B las te rs " is a toy that consists o f a set o f two ceramic bal ls , each coated vvith a mixture o f su l fur and potassium chlorate. K.CIO3. When the two bal ls are struck together, a loud popping noise is produced as su l f l i r and potassium chlorate react w i th each other.

16. Identify one source o f t h e act ivat ion energy for this reaction. | l |

Base your answers to questions 17 through 18 on the reaction represented by the balanced equation below.

2H2(g ) + 0 : ( g ) ^ 2 H 2 0 ( / ) + 571.6 k J

17, Identify' the infonnat ion in this equation that indicates the reaction is exo ihennic . [ t ]

18. E x p l a i n why the entropy o f the system decreases as the reaction proceeds, [ l ]

Base your answers to question 19 on the information below.

T h e equi l ibr i iun equation below is related to the manufacture o f a bleaching solut ion. In this equation, C l- (aq) means that chlor ide ions are sun-ounded by water molecules.

GMg) + 20H-(iiq) OCl-(aq) + Cl-i;ui' + \ W m 19. E x p l a i n , in terms o f co l l i s ion theor>', why increasing the concentration o f Cl2(g) increases the concentration o f OCI- (aq ) in this equi l ibr ium system, [ i j

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Base your answers to questions 20 and 21 on the in format ion below.

A gasol ine engine bums gasol ine in the presence o f excess oxygen to fonn carbon d ioxide and water. T h e main components o f gasol ine are isomers o f octane. A stnictural fonnu la o f octane is shown below.

H H H H H H H H I I I I I i I I

H ~ C ~ C - C - C - C - C - C ~ C ~ H I I I I I 1 I I

H H H H H H H H

One isomer o f octane is 2,2,4-trimetliylpentane.

20. In the space in your answer booklet, draw a stnictural fonnu la for 2,2,4-trimethylpentane. f i j

2 1 . E x p l a i n , in tenns o f t h e arrangement o f pan ic les , why the entropy o f gasoline vapor is greater than the entropy o f l iquid gasol ine, [ l ]

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Topic 7: Water & Solutions

1. Water has some unusual properties. •'' The bonds between H and 0 inside a water molecule are "polar covalent."

Due to its structure, it is a polar molecule. This means it has an uneven distribution of electrons in it. The 0 end is {-) and the H ends are (+). Oraiv/ts Lmis dot Structure fjsr^/ Water is actually a VERY polar substance. As a result, it uses the very strong type of intermolecular (between molecule) forces of attraction called "HYDROGEN BONDS."

^ As a result of H-bonding, water has an unusually high melting point and boiling point compared with similar molecules like H2S.

^ Water has a very high specific heat, so it heats up and cools down much more slowly than most materials. This value is found on Table B. Water solutions that contain ions are capable of conducting electricity. The substances that form the ions in solution are called "electrolytes."

2. Water is able to make solutions with many substances. ^ Solutions are ALWAYS HOMOGENEOUS MIXTURES. ^ Water will dissolve many ionic compounds.

Water will dissolve molecular substances if they are also polar. This reminds us of the "like dissolves like" principle. Acids dissolve in water to form H* ions. (This includes organic acids: R-COOH)

^ Bases dissolve in water to form OH ions. (This does NOT include alcohols: R-OH)

3. Ionic compounds may be either soluble or insoluble in water. ^ Use Table F to decide!

4. Solubility describes how much of a particular solute will dissolve in a set amount ofwater at a certain temperature.

Use Table G. The amount of water used is 100 g. Saturated solutions hold all the solute possible at the temperature chosen for the water. An increase in temperature of the water usually makes it capable of dissolving more solute. The opposite is true for gas solutes like O2 gas, or NH3 or SO2 or HCI. An increase in pressure over the solution increases the solubility of gas solutes. It does not affect solubility of solutes that are liquids or solids.

5. Solutions have a lower freezing point and a higher boiling point that pure water. This effect becomes larger with more concentrated solutions.

6. "Concentration" describes how much solute is dissolved in a certain amount of water.

You should know how to calculate: o Molarit/ o % mass o Parts per million

• Use Table T and "plug and chug."

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Water & Solutions -Cut from Jan 2007 - Jan 2008 E.\ains

1. A 3,0 M l-ICI(aq) solution contains a total o f ( 1 ) 3.0 grams o f MCI per liter o f water ( 2 ) 3.0 grams o f H C I per mole o f solution ( 3 ) 3.0 moles o f H C I per liter o f solution ( 4 ) 3.0 moles o f H C I per mole o f w a t e r

2. A di lute, aqueous potassium nitrate solution is best c lass i f ied as a ( 1 ) homogeneous compound ( 2 ) homogeneous mixture ( 3 ) heterogeneous compound ( 4 ) heterogeneous mixture

3. Acco rd ing to one acid-base theory, a water molecule acts as an acid when the water molecule ( 1 ) accepts an H" ( 3 ) donates an H (2 ) accepts an OH- ( 4 ) donates an O H

4. A n Ar rhen ius base y ie lds w h i c h ion as the only negative ion in an aqueous solution?

( 1 ) hydride ion ( 3 ) hydronium ion (2 ) hydrogen ion ( 4 ) hydroxide ion

5. Wh i ch bar ium salt is insoluble in water? ( L ) BaCO, i ( 3 ) Ba(C10.i)2 ( 2 ) BaCl2 ( 4 ) Ba (N0 j ) 2

6 . Wh i ch unit can be used to express solut ion concentration?

( 1 ) J/mol ( 3 ) m o l / L ( 2 ) L/mol ( 4 ) mol/s

7. Under w h i c h condit ions o f temperature and pressure is a gas most soluble in water? ( 1 ) high temperature and low pressure ( 2 ) high temperature and high pressure ( 3 ) low temperature and low pressure ( 4 ) low temperature and high pressure

8. G i v e n the equation representing a system at equ i l ibr ium:

At w h i c h temperature does this equi l ibr ium exist at 101,3 k i lopasca ls?

( 1 ) 0 K ( 3 ) 3 2 K ( 2 ) O X ( 4 ) 2 7 3 X

9, A s water is added to a 0.10 M N a C l aqueous solut ion, the conduct iv i ty o f the result ing solut ion ( 1 ) decreases because the concentrat ion o f ions decreases ( 2 ) decreases, but the concentration o f ions remains the same ( 3 ) increases because the concentrat ion o f ions decreases ( 4 ) increases, but the concentration o f ions remains the same

10, Wh i ch substance is an Ar rhen ius acid? ( 1 ) Ba{0H)2 (3)H3P04 ( 2 ) CH.X00CH. i ( 4 ) NaCI

I 1. Wh i ch compound releases hydroxide ions in an aqueous solution?

( U C H i C O O H ( 3 ) HCI (2 ) CH30H ( 4 ) KOH

12. Wh i ch l iquid has the highest vapor pressure at 7 5 X ?

( 1 ) ethanoic ac id ( 3 ) propanone ( 2 ) ethanol ( 4 ) water

13. Wh i ch sample o f matter is a single substance? ( 1 ) a ir ( 3 ) hydrochlor ic ac id ( 2 ) ammonia gas ( 4 ) salt water

14. A t standard pressure, a certain compound has a low boi l ing point and is insoluble in water. At S T P . this compound most l i k e l y ex is ts as

( 1 ) ionic c i ys ta l s ( 2 ) metal l ic cr>'Stals ( 3 ) nonpolar molecu les ( 4 ) polar molecu les

15. A n unsaturated solut ion is fonned when 80. grams o f a salt is d isso lved in 100. grams o f water at 4 0 . X . T h i s salt cou ld be

( 1 ) KCI ( 3 ) NaCI ( 2 ) KN03 ( 4 ) NaN03

16. Wh i ch substance, when d isso lved in water, fonns a solution that conducts an electr ic current?

( 1 ) C2H50H (3)Cl2H220ll ( 2 ) C 6 H i 2 0 6 ( 4 ) C H . 3 C O O H

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17. Compared to a 2,0 M aqueous solution o f NaC I at I atmosphere, a 3,0 M aqueous solution o f NaCl al 1 atmosphere has a ( I } lower boi l ing point and a higher freezing

point ( 2 ) lower boi l ing point and a lower freezing

point ( 3 ) higher boi l ing point and a higher freezing

point ( 4 ) higher boi l ing point and a lower freezing

point

18. A student prepares four aqueous solutions, each wi th a different solute. T h e mass o f each dissolved solute is shown in the table below.

Mass ot Dissolved Solute tor Four Aqueous Solutions

Solut ion Number

S o l u t e M a s s ot D i s s o l v e d So lute .;per too. g ot H , 0 at 2 0 . ' C i

1 K l 120 g

2 8 8 g

3 K C I 2 5 3

t K C I O , 5 g

Which solution is saturated? { 1 ) 1 ( 3 ) 3 ( 2 ) 2 ( 4 ) 4

Base your answers to question 19 on the information below.

The equi l ibr ium equation below is related to the manufacture o f a bleaching solut ion. In this equation,

C I (aq) means that chloride ions are surrounded by water molecules.

19. Draw rwo water molecules in the bos. showing the correct orientation o f each water molecule toward the chlor ide ion. [ i ]

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Base your answers lo quest ions 20 through 22 on the infonnat ion below.

Scient ists who study aquatic ecosystems are often interested in the concentration o f dissolved oxygen in water. O.xygen. O2. has a \ei-y low solubi l i ty in water, and therefore its so lubi l i ty is usual ly expressed in units o f mi l l ig rams per 1000. grams o f w a t e r at 1.0 atmosphere. T h e graph below shows a solubi l i ty curve o f oxygen in water.

S o l u b i l i t y o f O x y g e n i n W a t e r V e r s u s T e m p e r a t u r e

15.0-

II 10.0-

5 4 ' S ' - 5.0

S i N

I—' N

to, 20. 30.

Tempera tu re ( ' C )

20. A student detennines that 8.2 mi l l ig rams o f o.xygen is d issolved in a 1000.-gram sample o f water al \5°C and I.O atmosphere. In terms o f saturation, what type o f solution is this sample? [ I ]

2 1 . E x p l a i n , in terms o f mo lecu la r polarity, w h y oxygen gas has low solubi l i ty in water. Y o u r response must include bo/fi oxygen and water. [ I ]

22 . A n aqueous solution has 0 .0070 gram o f oxygen d issolved in 1000. grams o f water. Ca lcu la te the dissolved oxygen concentrat ion o f this solution in pans per m i l l i on . Y o u r response must include both a correct numerica l setup and the calculated result. [2 ]

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Base your answers to questions 23 and 24 on the infonnat ion below.

A solution is made by completely d issolv ing 90. grams o f K N O ^ s ) in 100. grams o fwa t e r in a beaker. The temperature o f this solution is 65°C.

23. Descr ibe the effect on the solubilit>' o f K N 0 3 ( s ) in this solution when the pressure on the solution increases. | i |

24. Detennine the total mass of K N 0 3 ( s ) that settles to the bottom o f the beaker when the original solution is cooled to \ | i |

Base your answers to questions 25 through 27 on the infonnation below.

T h e compound 1,2-ethanediol can be m i x e d wi th water. T h i s mixture is added to automobile radiators as an engine coolant. The cool ing system o f a smal l van contains 6690 grams o f 1,2-ethanediol. Some properties o f water and 1,2-cthanediol are given in the cable below.

Properties ot Water and 1,2-ethanedio!

Property Water i H , , 0 )

1 .2-e thaned l t ) l ( C H j O H O H j O H i

gram-formula m a s s igmrM) 1 8 , 0 S2.IJ

f a i l i n g f x i n t at a ta r tdard p r e s s u r e f C ) 1 » , 0 1 9 7 , 2

25, Identify the c lass o f organic compounds to wh i ch 1,2-ethanediol belongs, | l |

26. State, in tenns o f molecular polarity, w h y 1.2-ethanediol is soluble in water. 11 (

27. Ca lcu late the total number o f moles o f 1, 2-ethanediol in the smal l van ' s cool ing system. Y o u r response must include both a coiTect numer ica l setup and the calculated result, 12]

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28 , A n aqueous solution contains 300. parts per m i l l i on o f KOH. Detenn ine the number o f grams o f KOH

present in 1000. grams o f this solution, [i]

29. A l iqu id boils when the vapor pressure o f the l iquid equals the atmospheric pressure on the surface o f the l iqu id . Us ing Reference Tab l e H. detennine the boi l ing point o f w a t e r when the atmospheric pressure is 90. kPa . [1]

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