Stoichiometry (Chemical Calculations) and

the Mole Concept

6

These skills are usually tested on the SAT Subject Test in Chemistry. You
should be able to...

Use the mole concept to find the molar mass of formulas and of

monoatomic and diatomic molecules, and how gas volumes are

related to molar mass.

Solve stoichiometric problems involving Gay-Lussac’s Law,

density, mass–volume relation, mass–mass problems, volume–

volume problems, problems with a limiting reactant (excess of one

reactant), and finding the percent yield.

This chapter will review and strengthen these skills. Be sure to do the
Practice Exercises at the end of the chapter.

This chapter deals with the solving of a variety of quantitative chemistry

problems, which is often referred to as stoichiometry. Solving problems should
be done in an organized manner, and it would be to your advantage to go back to
the Introduction to this book and review the section called, “How Can You
Improve Your Problem Solving Skills?” It describes a well-planned method for
attacking the process of solving problems that you will find helpful in this chapter.
Although there are many specific methods for solving the types of problems
in this chapter, we will focus primarily on the technique called dimensional
analysis. Dimensional analysis provides a very clear problem-solving pathway
for stoichiometry problems. It emphasizes not only the numerical values involved
in the calculations but also the units describing the quantities in question.
Dimensional analysis was introduced in Chapter 1 to make unit conversions. It
will be used here in the same manner but specifically to relate quantities of
reactants and products in a chemical reaction.

TIP

Just as a dozen is 12 units of an item, a mole is 6.02 × 10^23 units of an item. It is called