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Unit 7: Chemical Equations
Chemistry
Evidence of a chemical reaction:
A reaction has occurred if the chemical and physical
properties of the reactants and products differ.
heatlight
soundgas emittedcolor change
odor
For a reaction to occur,particles of reactantsmust collide, and withsufficient energy
collision theory
activation energy:
Chemical reactions release or absorb energy.
energy needed to start a reaction
exothermicreactions
endothermicreactions
The reaction in an oxy-acetylene torch is exothermic.
Photosynthesis is anendothermic reaction.
catalyst: speeds up reaction wo/being consumed … it lowers the activation energy (AE)
AEAE
time time
without catalyst with catalyst
Examples: enzymes catalyze biochemical reactions catalytic converters convert CO into CO2
Ener
gy
Reaction Conditions and Terminology
Certain symbols give more info about a reaction.(s) = solid (l) = liquid (g) = gas
(aq) = aqueous(dissolved in H2O) NaCl(s) NaCl(aq)
More on aqueous…
-- “soluble” or “in solution” also indicate that a substance is dissolved in water (usually) -- acids are aqueous solutions
Other symbols…
means...
Temp. at which we perform rxn. might be given.
The catalyst used might be given.
means ______ is added to the reaction
MgCO3(s) MgO(s) + CO2(g)
C2H4(g) + H2(g) C2H6(g) Pt
C6H5Cl + NaOH C6H5OH + NaCl 400oC
“yields” or “produces”
heat
(i.e., clues about the reaction)
precipitate: a solid product that forms in an aqueous solution reaction
Na2CO3 + Ca(NO3)2 CaCO3 +(aq) (aq)
Na1+Ca2+CO3
2–
NO31–
2 (aq)(s)
Na1+
NaNO3
NO31–
ppt
clearNa2CO3
solution
clearCa(NO3)2
solution
cloudy solutioncontaining CaCO3(s)
and NaNO3(aq)
“chunks”“sinkies”“floaties”
Factors that influencethe rate of a reaction
To make reactionrate increase…
concentration of reactants
particle size
temperature
mechanical mixing
pressure
catalyst use onenature of reactants N/A
In a reaction:
atoms are rearranged
AND mass
energy
charge
are conserved
Balancing Chemical Equations
=law of
conservationof mass
same # of atomsof each type on each
side of equation
EX. solid iron reacts with oxygen gas to yieldsolid iron (III) oxide
If all coefficients are 1…
If we change subscripts…
Fe3+ O2– ___Fe(s) + ___O2(g) ___Fe2O3(s)
+
___Fe(s) + ___O2(g) ___Fe2O3(s) 11 1
___Fe2(s) + ___O3(g) ___Fe2O3(s) 11 1
+
Changing a ___________ changes the substance.
To balance, modify only _____________. Right now, _______________ don’t enter intoour “balancing” picture.
subscript
coefficientssuperscripts
___Fe(s) + ___O2(g) ___Fe2O3(s)
+
23
Hint: Start with most complicated substances firstand leave simplest substances for last.
4
2
solid sodium reacts w/oxygento form solid sodium oxide
___O2(g)___Na(s) ___Na2O(s)+
Na1+ O2–
+
14
Aqueous aluminum sulfate reacts w/aqueous calciumchloride to form a white precipitate of calcium sulfate.The other compound remains in solution.
Al3+ SO42– Ca2+ Cl1–
_ Al2(SO4)3(s)+ _ CaCl2 _ CaSO4 _ AlCl3(aq) (aq) (aq)+1 33 2
1
1
Methane gas (CH4) reacts withoxygen to form carbon dioxidegas and water vapor.
_ CH4(g) + _ O2(g) _ CO2(g) _ H2O(g)+2 1 2
_ CaC2(s) + _ H2O(l) _ C2H2(g) + _ CaO(s)
_ CaSi2 + _ SbI3 _ Si + _ Sb + _ CaI2
_ Al + _ CH3OH _ Al(CH3O)3 + _ H2
1 1 1
3 2 26 3
3262 13
Furnaces burnprimarily methane.
2_ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l) ** 5 4 21 2 1
1_ C3H8 + _ O2 _ CO2 + _ H2O ** 5 3 4
1_ C5H12 + _ O2 _ CO2 + _ H2O ** 8 5 6
** = complete combustion of a hydrocarbonyields CO2 and H2O
Write equations for the combustionof C7H16 and C8H18.
1_ C7H16 + _ O2 _ CO2 + _ H2O 11 7 8
1_ C8H18 + _ O2 _ CO2 + _ H2O 25 8 92 16 18
Classifying Reactions
four types
synthesis: simpler substances combine to form more complex substances
oxygen + rhombic sulfur sulfur dioxide
sodium + chlorine gas sodium chloride
A + B AB AB + C ABC A + B + C ABC
__ O2 __ S8+ __ SO2
__ Na __ Cl2+ __ NaCl
8 1 8
2 1 2
decomposition: complex substances are broken down into simpler ones
lithium chlorate lithium chloride + oxygen
water hydrogen gas + oxygen gas
Li1+ ClO31– Li1+ Cl1–
_ LiClO31 _ LiCl + _ O212 2 3
_ H2O2 _ H2 + _ O22 1
AB A + B ABC AB + C ABC A + B + C
single-replacement: one elementreplaces another
AB + C A + CB AB + C B + AC
chlorine sodiumbromide
sodiumchloride bromine + +
? aluminum copper (II)sulfate +
_ Cl2 Na1+ Br1– _ NaBr1 _ Br2 +
Na1+ Cl1– _ NaCl +2 2 1
Cu2+ SO42–
_ CuSO4_ Al +Al3+ SO4
2– _ Al2(SO4)31 _ Cu+32 3
copper aluminumsulfate +
double-replacement: AD + CBAB + CD
iron (III)chloride + potassium
hydroxide?
Fe3+ Cl1– _ FeCl3 +1
K1+ OH1– _ KOH
Fe3+ OH1– K1+ Cl1– _ KCl_ Fe(OH)3 +3 1 3
iron (III)hydroxide+ potassium
chloride
lead (IV)nitrate + calcium
oxide ?
Pb4+ O2– _ Pb(NO3)4 +1
Ca2+ NO31–
_ CaO _ Ca(NO3)2_ PbO2 +2 1 2Pb4+ O2– Ca2+ NO3
1–
lead (IV)oxide + calcium
nitrate
1
How do we know if a reaction will occur?
For single-replacement reactions, use Activity Series.In general, elements above replace elements below.
_ Ba + _ FeSO4
_ Mg + _ Cr(ClO3)3
_ Pb + _ Al2O3
_ NaBr + _ Cl2
_ FeCl3 + _ I2
_ CoBr2 + _ F2
_ Fe + _ BaSO4
_ Cr + _ Mg(ClO3)2
NR
_ NaCl + _ Br2
NR
_ CoF2 + _ Br2
1 1 1
3 2 2 3
2 1
1 1
2 1
1 1
(?)
For double-replacement reactions,reaction will occurif any product is: water a gas a precipitate
driving forces
_ Pb(NO3)2(aq) + _ KI(aq)
_ KOH(aq) + _ H2SO4(aq)
_ FeCl3(aq) + _ Cu(NO3)2(aq)
H1+ OH1–
Fe3+ Cl1– NO31–
Pb2+ NO31– K1+ I1– Pb2+ NO3
1– K1+ I1–
Check new combinations to decide.
(?)
K1+ SO42–
Cu2+
H1+ OH1– K1+ SO42– (?) (?)
Cl1–
Cu2+ (?)
Fe3+ NO31– (?)
(ppt) (aq)
(aq) (water)
(aq) (aq)
NR
_ K2SO4(aq) + _ H2O(l)
_ PbI2(s) + _ KNO3(aq) 1 2 1 2
2 1 1 2
Ions in Aqueous Solution Pb(NO3)2(s) Pb(NO3)2(aq)
Pb2+(aq) + 2 NO31–(aq)
addwater
dissociation:
Pb2+NO3
1–
NO31–
Pb2+
NO31–
NO31–
“splitting into ions”
NaI(s) NaI(aq) Na1+(aq) + I1–(aq)
Na1+ I1– Na1+ I1–add
water
Mix them and get the overall ionic equation…
__Pb2+(aq) + __NO31–(aq) + __Na1+(aq) + __I1–(aq)
__PbI2(s) + __NO31–(aq) + __Na1+(aq) yields
reactants
products
Cancel spectator ions to get net ionic equation… __PbI2(s)1
1 2 2 2
221
Pb2+
NO31–
NO31– Na1+ I1–
NO31–
NO31–
Na1+ I1–
Na1+
Na1+
__Pb2+(aq) + __I1–(aq) 1 2
Pb2+I1–
I1–
Pb2+I1–
I1–
Pb2+I1–
I1–
Mix together Zn(NO3)2(aq) and Ba(OH)2(aq):
Zn(NO3)2(aq) Ba(OH)2(aq)
Zn2+(aq) + 2 NO31–(aq) Ba2+(aq) + 2 OH1–(aq)
Ba2+
OH1–
OH1–
Zn2+
NO31–
NO31–
clear Zn(NO3)2 solution clear Ba(OH)2 solution
Mix them and get the overall ionic equation…
__Zn2+(aq) + __NO31–(aq) + __Ba2+(aq) + __OH1–(aq)
__Zn(OH)2(s) + __NO31–(aq) + __Ba2+(aq) yields
reactants
products
Cancel spectator ions to get net ionic equation… __Zn(OH)2(s)1
1 2 1 2
121
Zn2+
NO31–
NO31– OH1–
NO31–
NO31–
__Zn2+(aq) + __OH1–(aq) 1 2
Zn2+
OH1–
Ba2+
Ba2+Zn2+
OH1–
OH1–
OH1–
OH1–
Zn2+OH1–
OH1–
Polymers and Monomers
polymer: a large molecule (often a chain) made of many smaller molecules called monomers
Polymers can be made more rigid if the chains arelinked together by way of a cross-linking agent.
Monomer Polymer
amino acids…………
nucleotides (w/N-bases A,G,C,T/U)…..
styrene………………
PVA………………….
proteins
nucleic acids
polystyrene
“slime”polyvinylalcohol
H–N–C–C–O–HH H O
R
Quantitative Relationships in Chemical Equations
4 Na(s) + O2(g) 2 Na2O(s)
Particles 4 atoms 1 m’cule 2 m’cules
Moles 4 mol 1 mol 2 mol
Grams 4 g 1 g 2 g
** Coefficients of a balanced equation represent# of particles OR # of moles,but NOT # of grams.
When going from moles of one substance to molesof another, use coefficients from balanced equation.
part.
vol.
mass
MOL
mass
vol.
part.
MOL
SUBSTANCE “A” SUBSTANCE “B”(known) (unknown)
Use coeff. from balancedequation in crossing this bridge
4 Na(s) + 1 O2(g) 2 Na2O(s)
4 Na(s) + O2(g) 2 Na2O(s)
How many moles oxygen will react with 16.8 moles sodium?
How many moles sodium oxide are produced from87.2 moles sodium?
How many moles sodium are requiredto produce 0.736 moles sodium oxide?
( )4 mol Na
1 mol O216.8 mol Na = 4.2 mol O2
87.2 mol Na = 43.6 mol Na2O
( )2 mol Na2O4 mol Na0.736 mol Na2O = 1.472 mol Na
( )2 mol Na2O4 mol Na
O2Na Na2ONa2O Na
0 0