HC Unit 7: Chemical Equations
Name: ____________________
Evidence of a chemical reaction:
A reaction has occurred if the chemical and physical
properties of the reactants and products differ.
For a reaction to occur, particles of reactants must
collide, and with sufficient energy 
activation energy:
Chemical reactions release or absorb energy.
catalyst: speeds up reaction wo/being consumed
--
AE
AE
time
time
Examples:
--1
Factors that influence
the rate of a reaction
To make reaction
rate increase…
concentration of reactants
particle size
temperature
mechanical mixing
catalyst
nature of reactants
Balancing Chemical Equations
In a reaction:
To balance, modify only _____________. Changing a ___________ changes the substance.
Right now, _______________ don’t enter into our “balancing” picture.
SiCl4 +
H2O 
SiO2 +
Rule of Thumb A:
HCl
Au2S3 +
V2O5 +
HCl 
VOCl3 +
H2 
Au +
H2S
Rule of Thumb B:
H2O
Hg(OH)2 +
2
H3PO4 
Hg3(PO4)2 +
H2O
CaC2 +
H2O 
C2H2 +
CaSi2 +
SbI3 
Si +
CH3OH 
Al +
CaO
Sb +
Al(CH3O)3 +
C2H2 +
O2 
CO2 +
H2O
**
C3H8 +
O2 
CO2 +
H2O
**
C5H12 +
O2 
CO2 +
H2O
**
CaI2
H2
** =
Reaction Conditions and Terminology
Certain symbols give more info about a reaction.
(s) =
(l) =
(g) =
(aq) =
More on aqueous…
-- synonyms: “soluble” or “in solution”
-- acids and bases are aqueous solutions
Other symbols…
means…
 means _____ is added to the reaction.
Temp. at which we perform rxn. might be given.
The catalyst used might be given.
precipitate: a solid product that forms in an aqueous solution reaction
When ionic substances have “(aq)” written after them, the individual ions have
dissociated from the ionic crystal and are floating around separately.
3
Word Equations
Solid iron reacts with oxygen gas to yield solid iron(III) oxide.
word equation:
balanced equation:
Write a balanced equation (w/rxn conditions) from the following word equations.
EX.
Solid sodium reacts w/oxygen to form solid sodium oxide.
EX.
Aqueous aluminum sulfate reacts w/aqueous calcium chloride to form a white
precipitate of calcium sulfate. The other compound remains in solution.
EX.
Methane gas (CH4) burns in oxygen.
EX.
Write an equation for the combustion of C8H18.
4
Classifying Reactions  four types
A. synthesis: simpler substances combine to form more complex substances
sodium + chlorine gas  sodium chloride
B. decomposition: complex substances are broken down into simpler ones
lithium chlorate  lithium chloride + oxygen
C. single-replacement: one element replaces another
aluminum + copper(II) sulfate 
?
D. double-replacement:
lead(IV) nitrate + calcium oxide 
?
How do we know if a reaction will occur?
For single-replacement reactions,
Ba +
FeSO4 
use Activity Series. In general,
Mg +
Cr(ClO3)3 
elements above replace elements below.
Pb +
Al2O3 
NaBr +
Cl2 
FeCl3 +
I2 
CoBr2 +
F2 
For double-replacement reactions, reaction will occur if any product is:
Pb(NO3)2(aq) +
KOH(aq) +
FeCl3(aq) +
KI(aq) 
H2SO4(aq) 
Cu(NO3)2(aq) 
5
Polymers and Monomers
polymer: a large m’cule (often a chain) made of many smaller m’cules called monomers.
Polymers can be made more rigid if the chains are linked together by way
of a cross-linking agent.
Monomer
Polymer
amino acids………………………………..
nucleotides (w/N-bases A,G,C,T/U)……..
styrene……………………………………...
PVA…………………………………………
Quantitative Relationships in Chemical Equations
4 Na(s)
+
O2(g)

2 Na2O(s)
**
Particles
Moles
Grams
SUBSTANCE “B”
SUBSTANCE “A”
Mass
Use coeff. from bal. eq. to go
from “moles of A”
to “moles of B”
Vol.
MOL
MOL
EX.
4 Na(s) + O2(g)  2 Na2O(s)
How many moles oxygen will
react with 16.8 moles sodium?
EX.
How many moles sodium oxide are
produced from 87.2 moles sodium?
EX.
Vol.
Part.
Part.
Given the balanced equation…
Mass
How many moles sodium are required
to produce 0.736 moles sodium oxide?
6