Today is Wednesday, November 12 th, 2014 Pre-Class: What’s that? In This Lesson: Chemical...

Today is Wednesday,November 12th, 2014

Pre-Class:What’s that?

In This Lesson:Chemical Reactions

(Lesson 3 of 4)

Today’s Agenda

• Where we are and where we’ve been.• Chemical Reactions• Balancing Chemical Equations• Types of Chemical Reactions

• Where is this in my book?– P. 321 and following…

By the end of this lesson…

• You should be able to write, balance, classify, and predict chemical reactions.

A Wide-Range Review

• Way back, in a time called the beginning of the semester and a place called here, we talked about matter.

• We looked at its forms and properties.• We learned how to measure it and describe it.• We talked about what it’s made of (atoms)

and what atoms are made of too.

A Wide-Range Review

• Then we talked about electrons.• We talked about where we might find them at

any given time and how they’re arranged in elements.

• We talked about how chemists arrange elements in the periodic table.

• We learned how elements bond with one another.

A Wide-Range Review

• We also learned how to name the combinations they form.

• We learned another scale for measurement: the mole.

• We learned how to measure proportions and write formulas.

• Now, we’re going to learn how to write formulas for entire chemical reactions.

Chemical Reactions

• A chemical reaction is when a set of chemicals is changed into another set of chemicals.

• Reactions can be endergonic or exergonic.– Endergonic: Energy absorbed.– Exergonic: Energy released.• Exergonic reactions can happen spontaneously.• More on this to come in the next unit.

Chemical Reactions

• Previously, we discussed how reactions are shown in basic form:

• Reactants (starting stuff) are shown on the left of the equation.

• Products (ending stuff) are shown on the right of the equation.

• The arrow means “yields.”• Example:– Reactant(s) Product(s)– 4Fe + 3O2 2Fe2O3

Just checking…• Identify the reactant(s):– Na + Cl NaCl

• Na, Cl

• Identify the reactant(s):– 2H2O 2H2 + O2

• H2O

• Identify the product(s):– Na + Cl NaCl

• NaCl

• Identify the product(s):– 2H2O 2H2 + O2

• H2 + O2

One other thing…

• Don’t forget the symbols we covered back in the beginning of the year:– (s) means a chemical is in solid form.– (l) means a chemical is in liquid form.• Most liquids will be H2O for us.

– (g) means a chemical is in gaseous form.• Watch for BrINClHOF elements!

– (aq) means a chemical is in aqueous form – dissolved in water.• Acids are always (aq).

Lastly…• Don’t forget the BrINClHOF (diatomic) elements:– Bromine (Br2)– Iodine (I2)– Nitrogen (N2)– Chlorine (Cl2)– Hydrogen (H2)– Oxygen (O2)– Fluorine (F2)

• When these elements are on their own, they bond to themselves. YOU MUST REMEMBER THIS!!!!!!!!!!!!!!!!!!!!!1

Types of Reactions

• Now let’s talk about the types of chemical reactions.• For this class, you’ll need to know five of them:– Combination (also known as Synthesis)– Decomposition– Single Replacement– Double Replacement– Combustion

• Let’s take a look at them in chemistry terms as well as…prom terms.

1: Synthesis

+ “I told you they were together!”

1. Combination (Synthesis) Reactions

• In combination/synthesis reactions, two or more chemicals combine to make a new compound.– A + X AX

• Examples include:– Reactions with oxygen and sulfur.– Reactions of metals with halogens.– Reactions with oxides.

2: Decomposition

“Well we all saw that coming.”

+

2. Decomposition Reactions

• In decomposition reactions, a single compound breaks down into two or more simpler substances.– AX A + X

• Examples include:– [metal]CO3 [metal]oxide + CO2

– [metal]OH [metal]oxide + H2O

– [metal]ClO3 [metal]chloride + O2

– Acids [nonmetal]oxide + H2O

3: Single Replacement

“Scandalous!”

++

3. Single Replacement Reactions

• In single replacement reactions, a lone element takes the place of an element in a compound.– A + BX AX + B– BX + Y BY + X

• Examples include:– Metals replacing metals.– Hydrogen in water being replaced by a metal.– Hydrogen in acid being replaced by a metal.– Halogens being replaced by more reactive halogens.

Activity Series

• When we talked about Single Replacement Reactions, I mentioned “more reactive halogens.”

• As it turns out, elements (not just halogens) have varying degrees of reactivity.

• Chemists have created lists called Activity Series that detail how (in our class’s case) metals and halogens react with one another, assuming they even react at all.– Also known as Reactivity Series. Makes sense…

Activity Series of Metals

• Metals can replace other metals if they’re above the metal they’re replacing.

• Metals can replace Hydrogen in acids if they’re above Hydrogen.

• Metals can replace Hydrogen in water if they’re above Magnesium.

•Lithium•Potassium•Strontium•Calcium•Sodium•Magnesium•Aluminum•Zinc•Chromium•Iron•Nickel•Lead•HYDROGEN•Bismuth•Copper•Mercury•Silver•Platinum•Gold

Activity Series of Halogens

• A halogen can replace another halogen in a compound if it is above the one it’s replacing.

• Example:– 2NaCl (s) + F2 (g) 2NaF (s) + Cl2 (g)– MgCl2 (s) + Br2 (g) NO REACTION

• Note that the halogen activity series is the same as the group order of halogens on the table.

•Fluorine•Chlorine•Bromine•Iodine

Activity Series: Reaction or No?

• Cu + MgSO4 Mg + CuSO4

– No reaction (Magnesium is above Copper).

• Pb + ZnSO4 Zn + PbSO4

– No reaction (Zinc is above Lead).

• Fe + 2AgNO3 2Ag + Fe(NO3)2

– Reaction (Iron is above Silver).

• 2Al + 3H2O Al2O3 + 3H2

– No reaction (Aluminum is not above Magnesium).

Single Replacement Technicalities**Technically, this is important.

• When a Group I or Group II metal (alkali/alkaline earth) reacts with water, they only replace one of the hydrogens.

• Examples:– K + H2O KOH + O2

– Mg + H2O Mg(OH)2 + O2

• In other words, they form hydroxides, not oxides.

Aside: Coins

• There’s an interesting phenomenon with pocket change relating to the Activity Series:– Pennies tend to become very dull relatively quickly, yet

quarters and other “silvery” coins tend not to. What’s the deal?

• As it turns out, pennies are plated in copper, while other coins are plated in nickel. – Because nickel is higher on the list, it’s less likely to be

replaced and thus tarnish.– Copper, on the other hand, is a bit of a chemical “weakling.”

http://www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/series/3postlab.htm

http://www.usmint.gov/about_the_mint/index.cfm?action=coin_specifications

4: Double Replacement

“Gross!”

+ +

4. Double Replacement Reactions

• In double replacement reactions, ions of two compounds flip places in aqueous solutions, forming two new compounds.– AX + BY AY + BX

• Typically, one of the compounds formed is:– A precipitate (a solid or a bubblin’ gas).– A molecular compound (usually water).

• One of the compounds must be insoluble!

Reminder: Dissociation

CaCl

Cl

Ca2+Cl-

Cl-

Bound ions in… …component ions out.

Predicting States of Matter

• Remember that double replacement reactions occur in solutions.

• To predict the states of matter resulting from a double replacement reaction, first write the equation.

• Then, use your solubility table.– FYI, when they say “salts involving,” just think of it

as saying “ionic compounds involving…”– FYI, when they say “halides,” just think of it as

saying “halogens…”

Solubility Example

• NiNO3 (aq) + KBr (aq) → KNO3 (?) + NiBr (?)• In what states are potassium nitrate and nickel (I)

bromide?• According to your solubility table:– 1./2. All salts of Group IA and nitrates are soluble, so

potassium nitrate is.– 3. All salts of halides (halogens) are soluble, except… so

nickel (I) bromide is.

• NiNO3 (aq) + KBr (aq) → KNO3 (aq) + NiBr (aq)– So no reaction, since both of them are soluble.

• Remember, one must be insoluble!

Solubility Example

• Ba(NO3)2 (aq) + (NH4)3PO4 (aq) → NH4NO3 (?) + Ba3(PO4)2 (?)• In what states are ammonium nitrate and barium

phosphate?• According to the solubility table,– 1./2. All salts of ammonium and nitrates are soluble so

ammonium nitrate is.– 5. All salts of …phosphate… are insoluble except… so barium

phosphate is not.

• Ba(NO3)2 (aq) + (NH4)3PO4 (aq) → NH4NO3 (aq) + Ba3(PO4)2

(s)– One compound is insoluble, so there will be a reaction.

Precipitates

• In the previous example, Ba3(PO4)2 “fell out” of solution.– In other words, it took on a solid form and was no

longer dissolved.– We would expect it to collect at the bottom of the

container.• This is an example of precipitation, or the

formation of a precipitate.– A precipitate is a solid or gas substance that “falls

out” of an aqueous solution.• A precipitate could be water, but this is less common.

Precipitate Video/Demo

• KI (aq) + Pb(NO3)2 (aq) KNO3 (?) + PbI2 (?)• Check your solubility tables for the phase of the

two products.– 1./2. All salts of Group IA and nitrates are soluble, so

potassium nitrate is.– 3. All salts of halides are soluble except those of lead

(II), so lead (II) iodide is insoluble.

• KI (aq) + Pb(NO3)2 (aq) KNO3 (aq) + PbI2 (s)• [Video]

5: Combustion

+ This one’s hard to picture. Basically, oxygen reacts with something, usually releasing a lot of light and/or heat.

5. Combustion Reactions

• In combustion reactions, a substance reacts with oxygen, releasing a large amount of energy in the form of heat and light.

• When the reactants are only oxygen and a hydrocarbon, carbon dioxide and water are the products.– Hydrocarbons are compounds made of only hydrogen, carbon,

and/or oxygen.• Examples include:– C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (g)

– P4 (s) + 5O2 (g) P4O10 (s)• This is a combustion and synthesis reaction!

Combustion Reaction Demo

• C2H5OH + 3O2 2CO2 + 3H2O

Aside: Great Moments in Science

• Meet Pilatre de Rozier:• Mr. Rozier wanted to

test the flammability of hydrogen, so he inhaled some, then exhaled over an open flame.

• Result?– Singed eyebrows.

http://www.sciencephoto.com/image/228189/350wm/H4180269-Pilatre_de_Rozier,_French_balloonist-SPL.jpg

Identifying Chemical Reactions

• Let’s practice identifying chemical reactions:– Chemical Reactions Packet, Page 2, Upper Section• Don’t worry about balancing them yet.

Balancing Chemical Equations

• In addition to identifying chemical reactions, they also need to be balanced.

• According to the Law of Conservation of Mass/Matter, the mass of the reactants must equal the mass of the products.– Atoms are conserved.

• So, all chemical formulas must show the same AMOUNTS OF ATOMS on both sides of the arrow.– No elements can appear or disappear, either.

PhET

• Balancing Chemical Equations

Skeleton Equations

• Up till this point in the semester, sometimes we’ve been writing equations that are not balanced, just to describe which elements are reacting.

• These unbalanced equations are called skeleton equations.– Think “bare bones” equations.

• From now on, we’ll need to balance our equations, so here are some directions.

How to Balance Chemical Equations

• Under the arrow, vertically list each element.– Don’t use any additional subscripts.

• Put a box around each term in the equation.• Use coefficients to balance each side.– NOT subscripts.

• Balance hydrogen second-to-last and oxygen last.– How to remember this?

Balancing Chemical Equations Example

• ___Al + ___O2 ___Al2O3

Al

O

1 22 3

22

3 2

6 64

4

4

Important Note

• Keep in mind that, like in empirical formulas, the coefficients in a balanced equation should not be able to be reduced.

• In other words:– 2Na + 2Cl 2NaCl should really be– Na + Cl NaCl

• Even if it’s balanced, it has to be reduced to the lowest ratio.

Balancing Synthesis Reactions1 of 3

1. ___CaO + ___H2O ___Ca(OH)2

– CaO + H2O Ca(OH)2

2. ___P4 + ___O2 ___P2O5

– P4 + 5O2 2P2O5

3. ___Ca + ___O2 ___CaO– 2Ca + O2 2CaO

4. ___Cu + ___S8 ___ CuS– 8Cu + S8 8CuS


5. ___S8 + ___O2 ___SO2

– S8 + 8O2 8SO2

6. ___H2 + ___N2 ___NH3

– 3H2 + N2 2NH3

7. ___H2 + ___Cl2 ___HCl– H2 + Cl2 2HCl

8. ___Ag + ___S8 ___Ag2S– 16Ag + S8 8Ag2S


9. ___Cr + ___O2 ___Cr2O3

– 4Cr + 3O2 2Cr2O3

10.___Al + ___Br2 ___AlBr3

– 2Al + 3Br2 2AlBr3

11.___Na + ___I2 ___NaI– 2Na + I2

2NaI12.___H2 + ___O2 ___H2O– 2H2 + O2 2H2O

Balancing Decomposition Reactions1 of 3

1. ___BaCO3 ___BaO + ___CO2

– BaCO3 BaO + CO2

2. ___MgCO3 ___MgO + ___CO2

– MgCO3 MgO + CO2

3. ___K2CO3 ___K2O + ___CO2

– K2CO3 K2O + CO2

4. ___Zn(OH)2 ___ZnO + ___H2O– Zn(OH)2 ZnO + H2O


5. ___Fe(OH)2 ___FeO + ___H2O– Fe(OH)2 FeO + H2O

6. ___Ni(ClO3)2 ___NiCl2 + __O2

– Ni(ClO3)2 NiCl2 + 3O2

7. ___NaClO3 ___NaCl + ___O2

– 2NaClO3 2NaCl + 3O2

8. ___KClO3 ___KCl + ___O2

– 2KClO3 2KCl + 3O2


9. ___H2SO4 ___H2O + ___SO3

– H2SO4 H2O + SO3

10.___H2CO3 ___H2O + ___CO2

– H2CO3 H2O + CO2

11.___Al2O3 ___Al + ___O2

– 2Al2O3 4Al + 3O2

12.___Ag2O ___Ag + ___O2

– 4Ag2O 2Ag + O2

Balancing Single Replacement Reactions1 of 2

1. ___AgNO3 + ___Ni ___Ni(NO3)2 + ___Ag

– 2AgNO3 + Ni Ni(NO3)2 + 2Ag

2. ___AlBr3 + ___Cl2 ___AlCl3 + ___Br2

– 2AlBr3 + 3Cl2 2AlCl3 + 3Br2

3. ___NaI + ___Br2 ___NaBr + ___I2

– 2NaI + Br2 2NaBr + I2

4. ___Ca + ___HCl ___CaCl2 + ___H2

– Ca + 2HCl CaCl2 + H2

Balancing Single Replacement Reactions2 of 2

5. ___Mg + ___HNO3 ___Mg(NO3)2 + ___H2

– Mg + 2HNO3 Mg(NO3)2 + H2

6. ___ Zn + ___H2SO4 ___ZnSO4 + ___H2

– Zn + H2SO4 ZnSO4 + H2

7. ___K + ___H2O ___KOH + ___H2

– 2K + 2H2O 2KOH + H2

8. ___Na + ___H2O ___NaOH + ___H2

– 2Na + 2H2O 2NaOH + H2

Balancing Double Replacement Reactions1 of 3

1. ___AlI3 + ___HgCl2 ____AlCl3 + ____HgI2

– 2AlI3 + 3HgCl2 2AlCl3 + 3HgI2(s)

2. ___HCl + ___NaOH ___NaCl + ___H2O

– HCl + NaOH NaCl + H2O

3. ___BaCl2 + ___H2SO4 ___BaSO4 + ___HCl

– BaCl2 + H2SO4 BaSO4 + 2HCl

4. ___Al2(SO4)3 + ___Ca(OH)2 ___Al(OH)3 + ___CaSO4

– Al2(SO4)3 + 3Ca(OH)2 2Al(OH)3 + 3CaSO4


5. ___AgNO3 + ___K3PO4 ___Ag3PO4 + ___KNO3

– 3AgNO3 + K3PO4 Ag3PO4 + 3KNO3

6. ___CuBr2 + ___AlCl3 ___CuCl2 + ___AlBr3

– 3CuBr2 + 2AlCl3 3CuCl2 + 2AlBr3

7. ___Ca(C2H3O2)2 + ___Na2CO3 ___CaCO3 + __NaC2H3O2

– Ca(C2H3O2)2 + Na2CO3 CaCO3 + 2NaC2H3O2

8. ___NH4Cl + ___Hg2(C2H3O2)2 __NH4C2H3O2 + ___Hg2Cl2

– 2NH4Cl + Hg2(C2H3O2)2 2NH4 C2H3O2 + Hg2Cl2


9. ___Ca(NO3)2 + ___HCl ___CaCl2 + ___HNO3

– Ca(NO3)2 + 2HCl CaCl2 + 2HNO3

10. ___FeS + ___HCl ___FeCl2 + ___H2S

– FeS + 2HCl FeCl2 + H2S

11. ___Cu(OH)2 + ___HC2H3O2 ___Cu(C2H3O2)2 + ___H2O

– Cu(OH)2 + 2HC2H3O2 Cu(C2H3O2)2 + 2H2O

12. ___Ca(OH)2 + ___H3PO4 ___Ca3(PO4)2 + ___H2

– 3Ca(OH)2 + 2H3PO4 Ca3(PO4)2 + 6H2

Balancing Combustion Reactions1 of 3

1. ___CH4 + ___O2 ___CO2 + ___H2O– CH4 + 2O2 CO2 + 2H2O

2. ___C2H6 + ___O2 ___CO2 + ___H2O– 2C2H6 + 7O2 4CO2 + 6H2O

3. ___C3H8 + ___O2 ___CO2 + ___H2O– C3H8 + 5O2 3CO2 + 4H2O


4. ___C4H10 + ___O2 ___CO2 + ___H2O– 2C4H10 + 13O2 8CO2 + 10H2O

5. ___C5H12 + ___O2 ___CO2 + ___H2O– C5H12 + 8O2 5CO2 + 6H2O

6. ___C6H14 + ___O2 ___CO2 + ___H2O– 2C6H14 + 19O2 12CO2 + 14H2O


7. ___C2H4 + ___O2 ___CO2 + ___H2O

– C2H4 + 3O2 2CO2 + 2H2O

8. ___C2H2 + ___O2 ___CO2 + ___H2O

– 2C2H2 + 5O2 4CO2 + 2H2O

9. ___C6H6 + ___O2 ___CO2 + ___H2O

– 2C6H6 + 15O2 12CO2 + 6H2O

Balancing Equations Practice

• Chemical Reactions Packet (key online)• You must complete at least 3 problems in every

section on this packet (except page 4).• You must score 30 points or higher:– Page 1, Upper Section: 1 point each– Page 1, Lower Section: 2 points each– Page 2, Upper Section: 1 point each– Page 2, Lower Section: 2 points each• Includes Page 3 – must have states of matter.

Combustion Reaction Details

• Chemical Reactions Packet, Page 4

Predicting Products

• Here’s a little conceptual question:– If methane (CH4) combusts, what are the reactants and

what are the products?• Since combustion reactions always use oxygen gas

as a reactant and form water and carbon dioxide as products (if the other reactant is a hydrocarbon), the skeleton equation would look like this:– Skeleton: CH4 + O2 CO2 + H2O

– Balanced: CH4 + 2O2 CO2 + 2H2O

Predicting Products

• In addition to just spotting the type of reaction, it’s good to be able to predict the products of a reaction.

• Here’s a website to help:– http://www.files.chem.vt.edu/RVGS/ACT/notes/

Practice_Predicting.html– Also linked on my Chemistry Links page.

Predicting Products BIG HINTS

• Don’t worry about subscripts when predicting products.– Figure out who’s together and/or who’s alone.– THEN write subscripts.

• Also, don’t forget the diatomic (BrINClHOF) elements.

• Finally, make sure you’re replacing cations with cations (written first) and anions with anions (written second).

Reaction Type Summary

+ Double Replacement

+ Single Replacement

Decomposition

+ Synthesis

Combustion+O2

More Predicting Products Practice

• Now for reactions other than combustion:– Equations Worksheet, Lower Section• First, just figure out the type of reaction.• Then predict the products.• Then balance.

– Predict the Products worksheet

Closure

• http://education.jlab.org/elementbalancing/index.html– Also linked on my Chemistry Links page.

• You may try 5, 10, or 15 questions (let’s go with 15 for today), and you may set the difficulty at easy, intermediate, or hard.

• Your goal is to do 15 easy questions, 15 intermediate questions, and 15 hard questions.– Let me know when you’re done.

Today is Wednesday, November 12 th, 2014 Pre-Class: What’s that? In This Lesson: Chemical...

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