Reaction Stoichiometry
Chapter 9
Reaction Stoichiometry

Reaction stoichiometry – calculations of
amounts of reactants and products of a
chemical reaction

Review significance of a balanced eqn:
2Mg + O2  2MgO
2 atoms Mg + 1 oxygen molecule  2 formula
units MgO
2 moles Mg + 1 mol oxygen  2 moles MgO
Since we can’t count out individual
atoms, molecules or formula units,
we will count the coefficients in
mole units.

Mole ratios: a conversion factor
that relates the amounts of two
different substances based on
the balanced eqn.

Ex: 2 mol Mg
2 mol MgO
1 mol O2
2 mol MgO
Molar Mass

Review of Molar Mass: mass of one mole of
substance.

The molar mass of H2O is 18.0 g. It can be
expressed as 1 mol H2O
18 g H2O
Express the molar mass of the
following in conversion factor form:
a) Al2O3
b) C12H22O11
Section Review p 277
Stoichiometric Calculations
Steps to Solving Stoichiometry Problems:
1.
Balanced Eqn. Write given and unknown
under eqn.
2.
Convert given to moles
3.
Mole Ratio: unknown/known
4.
Covert to unit needed.
Mass – Mass Calculations
In a lab, solid substances are usually
measured out in grams.
1. How many grams of SnF2, used in
toothpaste, are produced from the
reaction of 30 g of HF with Sn?
Prac p287 and section review p287
Cu + AgNO3  Cu(NO3)2 + Ag
2.
a.
b.
How many grams of silver will be
produced if 125 g of copper is
reacted with silver nitrate.
How many grams of copper is
needed to complete the rxn if 200
g of silver nitrate is used?
3. A camping lantern uses the reaction of
calcium carbide, CaC2 (s), and water
to produce acetylene gas, C2H2(g), and
calcium hydroxide, solid. How many
grams of water are required to
produce 1.55 moles of acetylene gas?

Prac Problems p 282 -284.
Limiting Reactants


Limiting reactant – reactant that runs out first
and limits the amount of product produced.
Excess reactant – the substance that is not used
up in a rxn.
Strategy
1. Take each reactant amount and calculate the amount
of one product it will make. The reactant that
makes the smallest amount of product is the
limiting reactant. The other is the excess reactant.
2. Calculate amount of excess reactant needed based
on the limiting reactant quantity.
3. Determine amounts of products based on limiting
reactant amt.
1. If 1.21 moles of solid zinc are added to 2.65
moles of hydrochloric acid, HCl, then zinc
chloride, ZnCl2 (aq), and hydrogen gas are
formed. Determine which reactant is in excess
and by what amount and calculate the number
of moles of each product.
Step 1: Determining limiting reactant.
Step 2: Determining amt of excess reactant
needed.
Step 3: Determining amt of rest of products.
2.
Given the following rxn:
3Fe + 4H2O  Fe3O4 + 4H2
a. When 36 g of water is mixed with
167 g of Fe, which is the limiting
reactant?
b. What mass in grams of iron oxide is
produced?
c. What mass in grams of excess
remains when the reaction is
completed?


Do prob on p289 prac #1 and #2.
The sample problem 9-7 p290. More practice
on p291
Percent Yield

Percent yield = actual yield * 100
theoretical yield
Actual yield = amt of product obtain from
experiment
Theoretical yield = maximum amt of product can
be produced according to calculations.

Read sample prob 9-8 p293, then set up bal eqn and
the given info and the unknown:
C6H6
38.8 g
38.8 g
+
Cl2  C6H5Cl +
excess 38.8 g actual

? g theoretical
HCl
A x 100  % yield of C6H5Cl
T
Prac p 294 and section review p 294
Given the following equation:
C6H6 + Cl2  C6H5Cl + HCl
When 36.8 g of C6H6 react with an excess of
chlorine, the actual yield of C6H5Cl is 38.8 g.
What is the percent yield of C6H5Cl ?
1.