Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
114 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 11
10. Aluminum reacts with chlorine to produce aluminum chloride.
a. Balance the equation: Al(s) ϩ Cl 2 (g) 0 AlCl 3 (s).
b. If you begin with 3.2 g of aluminum and 5.4 g of chlorine,
which is the limiting reactant?
c. How many grams of aluminum chloride can be produced
from the amount of limiting reactant available?
d. Calculate the mass of excess reactant that remains after the
reaction is complete.
Reactions do not always continue until all of the reactants are used
up. Using an excess of the least expensive reactant in a reaction can
ensure that all of the more expensive reactant is used up, making the
chemical reaction more efficient and cost-effective. Using an excess
of one reactant can also speed up some reactions.
11.4 Percent Yield
Most chemical reactions do not produce the predicted amount of product. Although your work so far with stoichiometric problems may
have led you to believe that chemical reactions proceed according to
the balanced equation and always produce the calculated amount of
product, it’s not true. Many reactions stop before all the reactants are
used up, so less product is formed than expected. Also, products other
than those expected sometimes form from competing chemical reactions, thereby reducing the amount of the desired product.
The theoretical yield is the maximum amount of product that
can be produced from a given amount of reactant under ideal circumstances. This is the amount you have been calculating in
practice problems so far. Chemical reactions hardly ever produce the
theoretical yield. The actual yield is the amount of product that is
actually produced when a chemical reaction is carried out in an
experiment. It is determined by measuring the mass of the product.
Percent yield of product is the ratio of the actual yield to the theoretical yield expressed as a percent.
Percent yield ϭ
ϫ 100
actual yield (from an experiment)
ᎏᎏᎏᎏᎏᎏ
theoretical yield (from stoichiometric calculations)
114 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 11
10. Aluminum reacts with chlorine to produce aluminum chloride.
a. Balance the equation: Al(s) ϩ Cl 2 (g) 0 AlCl 3 (s).
b. If you begin with 3.2 g of aluminum and 5.4 g of chlorine,
which is the limiting reactant?
c. How many grams of aluminum chloride can be produced
from the amount of limiting reactant available?
d. Calculate the mass of excess reactant that remains after the
reaction is complete.
Reactions do not always continue until all of the reactants are used
up. Using an excess of the least expensive reactant in a reaction can
ensure that all of the more expensive reactant is used up, making the
chemical reaction more efficient and cost-effective. Using an excess
of one reactant can also speed up some reactions.
11.4 Percent Yield
Most chemical reactions do not produce the predicted amount of product. Although your work so far with stoichiometric problems may
have led you to believe that chemical reactions proceed according to
the balanced equation and always produce the calculated amount of
product, it’s not true. Many reactions stop before all the reactants are
used up, so less product is formed than expected. Also, products other
than those expected sometimes form from competing chemical reactions, thereby reducing the amount of the desired product.
The theoretical yield is the maximum amount of product that
can be produced from a given amount of reactant under ideal circumstances. This is the amount you have been calculating in
practice problems so far. Chemical reactions hardly ever produce the
theoretical yield. The actual yield is the amount of product that is
actually produced when a chemical reaction is carried out in an
experiment. It is determined by measuring the mass of the product.
Percent yield of product is the ratio of the actual yield to the theoretical yield expressed as a percent.
Percent yield ϭ
ϫ 100
actual yield (from an experiment)
ᎏᎏᎏᎏᎏᎏ
theoretical yield (from stoichiometric calculations)