Chemistry Reference
In-Depth Information
In Chapter 7, we learned to interpret chemical formulas in terms of the quanti-
ties of the elements involved. In Chapters 8 and 9, we learned to complete and
balance chemical equations. This chapter shows how to interpret the quantities
of substances involved in a chemical reaction, using the balanced chemical
equation almost as the formula was used in Chapter 7.
Just as compounds have definite ratios of elements, chemical reactions have
definite ratios of reactants and products. Those ratios are used in Section 10.1
to calculate the number of moles of other substances in a reaction from the num-
ber of moles of any one of the substances. Section 10.2 combines information
from Section 10.1, Chapter 7, and elsewhere to explain how to calculate the
mass of any substance involved in a reaction from the mass of another. Section
10.3 demonstrates how to work with quantities in units other than moles or
masses when finding quantities of reactants or products. Section 10.4 shows how
to calculate the quantities of substances involved in a reaction even if the quan-
tities of reactants present are not in the mole ratio of the balanced equation.
Section 10.5 covers the calculation of the percentage yield of a product from
the actual yield and the theoretical yield, based on the amount(s) of reactant(s).
Section 10.6 explains which of these types of calculations can and cannot be
done with net ionic equations.
10.1
Mole Calculations for Chemical Reactions
Stoichiometry
involves the calculation of quantities of any substances involved
in a chemical reaction from the quantities of the other substances. The balanced
equation gives the ratios of formula units of all the substances in a chemical
reaction. It also gives the corresponding ratios of moles of the substances. These
relationships are shown in Figure 10.1. For example, one reaction of phosphorus
with chlorine gas is governed by the equation
2 P(s)
3 Cl
2
(g) £ 2 PCl
3
(
/
)
Figure 10.1
Mole Conversions
for Stoichiometry Problems
The double-headed arrows indicate
that the conversions can be made in
either direction.
Moles of
reactant
or product A
Balanced
chemical
equation
Moles of
reactant
or product B
Avo
gadr
o's
n
umbe
r
Avo
gad
ro's
n
umb
er
Formula units
of reactant
or product A
Balanced
chemical
equation
Formula units
of reactant
or product B
