Unit IV: Chemical Equations
& Stoichiometry
A.
B.
The chemical equation
Types of chemical reactions
A.
B.
C.
D.
E.
F.
G.
Activity series of metals
Solubility rules
Rules for writing and balancing
equations
Calculations from chemical equations
Limiting reactant
Applications of stoichiometry
Theoretical and percent yeild
The Chemical Equation
Word equations:
Solid potassium chlorate, when
heated, decomposes to produce solid
potassium chloride and oxygen gas.
Chemical equation:
∆
2 KClO3(s)  2KCl(s) + 3 O2(g)
4-A
The Chemical Equation
Convert the following word equations into a
chemical equation:
Aqueous silver nitrate reacts with aqueous
strontium chloride to form a silver chloride
precipitate and a solution of aqueous strontium
nitrate.
Solid iron (III) oxide and aluminum powder
are heated and react to form solid aluminum
oxide and liquid iron.
Classes of Chemical Reactions
Combination
Decomposition
Single Replacement
Double Replacement
–
Neutralization
Combustion
Evidence for a Chemical Change
Heat being released (exothermic) or
absorbed (endothermic)
Light is given off
Color change
Evolution of gas
Precipitate forms when solutions are mixed
Formation of new substances
Combination (synthesis)
Reaction

General form of combination reaction
A+BC
Ex. Iron and oxygen
2Fe(s) + 3O2(g)  2Fe2O3(s)
Decomposition Reaction
General form of the equation
AB  A + B
An example would be nitrogen
triiodide
2 NI3 (s) → N2 (g) + 3 I2 (g)
Demonstration
Single Replacement
Reaction
A + BD  AD + B
Here A represents a metal, B a metal
ion and D an anion. If A is more
active than B it will replace it.
Ex. Aluminum + Iron (III) oxide
Demonstration
Activity series
Most Reactive
Mg  Mg2+
Al  Al3+
Zn  Zn2+
Fe  Fe2+
Ni  Ni2+
Sn  Sn2+
Pb  Pb2+
H2(g) 2H+(aq)
Cu
Ag
Hg
Au
 Cu2+
 Ag+
 Hg2+
 Au3+
Least Reactive
Double Replacement
Reaction
General form of the equation
AB + CD  AD + CB
The cation and anion of one compound
switch with those of another

Ex. Mercury (II) chloride and sodium
iodide
Demonstration
Solubility Rules
All compounds with Group IA or NH4+ cations are soluble
in water
All compounds with nitrate and acetate anions are
soluble in water
All halides (F-, Cl-, Br-, I-) are soluble except in
compounds with Ag+, Pb2+, Hg22+
All sulfates are soluble except with Ba2+, Sr2+, Ca2+, and
Pb2+
See the Table on page 109 of your manual for a more
complete list of some solubility rules
Combustion Reaction

General equation:
Hydrocarbon + O2  CO2 + H2O
The oxygen can come from a variety of
sources
Ex. Oxidation of glycerin
14 KMnO4 + 4 C3H5(OH)3 7 K2CO3 + 7 Mn2O3 + 5 CO2 + 16
H2 O
Demonstration
Lecture Problems 4-1 pg. 111
Write complete chemical equations for the following
and include their classification
a. Al (s) + O2 (g)  aluminum oxide
b. ammonia gas  hydrogen gas + nitrogen gas
c. C6H12 (l) + oxygen gas  CO2 (g) + H2O (g)
d. (NH4)2SO4 (aq) + BaCl2 (aq)  barium sulfate
ammonium chloride (aq)
(s)
Extra practice:
Al (s) + copper (II) sulfate
copper (s) + aluminum sulfate (aq)
(aq)
+

Rules for Balancing Equations
1. Write the correct formulas for reactants and
products.
2. Count and compare the number of atoms of
each element on both sides of the equation
3. Balance the elements one at a time, by using
stoichiometric coefficients in front of the
necessary compounds.
Remember! Never change the actual formula of a
compound to balance the equation
Rules for Balancing Equations
4. Start with the most complicated compound first. (The
one with the most atoms)
5. Make sure as you work through each element you note
any others that become unbalanced.
6. Try balancing oxygen and hydrogen last.
7. Polyatomic groups that are not changed during the
reaction are balanced as groups.
8. The numbers used (stoichiometric coefficients) to
balance an equation should be in the smallest ratio
possible.
Lecture Problem IV-2 (pg. 113)
a.
__Fe(s) + __O2(g) –> __Fe2O3(s)
Solid iron combines with oxygen gas to form solid iron (III) oxide.
b.
__Mg(s) + __N2(g) –> ______(s)
Solid magnesium reacts with nitrogen gas to form solid magnesium nitride
d.
__Co2(CO3)3(s) –>__Co2O3(s) + __CO2(g)
Solid cobalt (III) carbonate decomposes to form solid cobalt (III) oxide
and carbon dioxide gas
f.
__AgClO3(s) –> __AgCl(s) + __O2(g)
Solid silver chlorate decomposes to form solid silver chloride and
oxygen gas
Lecture Problem IV-2 (pg. 114)
h. __Sn(s) + __HCl(aq) –> __SnCl2(aq) +__H2(g)
Tin metal reacts with hydrochloric acid to form aqueous tin (II)
Chloride and hydrogen gas.
j. __P4(s) + __N2O(g) –> __P4O6(s) + __N2(g)
Solid phosphorus reacts with dinitrogen monoxide to form solid
Tetraphosphorus hexaoxide and nitrogen gas.
l. __Pb(C2H3O2)2(aq) + __KI(aq)–>___(s) + __KC2H3O2(aq)
Aqueous lead (II) acetate reacts with aqueous potassium iodide to form
a solution of potassium acetate and a precipitate of lead (II) iodide.
o. __H2SO4(aq) + __KOH(aq)–> __K2SO4(aq) + __H2O(g)
Sulfuric acid is neutralized with potassium hydroxide to form a
solution of potassium sulfate.
Lecture Problem IV-2 (pg. 115)
q. __C8H18(l) + __O2(g) –> ____(g) +__H2O(g)
Liquid octane is burned in oxygen gas to form gaseous carbon dioxide
and water vapor.
r. __NH3(g) + __O2(g) –>__NO2(g) + __H2O(g)
Gaseous ammonia reacts with oxygen to form nitrogen dioxide gas
and gaseous water.
Extra Practice: Complete the Following
Magnesium metal reacts with H2SO4(aq) → …
CH3(CH2)3CH2OH + oxygen gas → …
NaHCO3 + HCl(aq) → aqueous sodium chloride +
water + carbon dioxide gas.
Sulfur and oxygen combine when heated to form
sulfur dioxide gas.
MgCO3 + heat → MgO + …
AgNO3(aq) + NaCl(aq) → ...