The Foundations of Chemistry

EXAMPLE 12-1 Boyle’s Law Calculation

A sample of gas occupies 12 L under a pressure of 1.2 atm. What would its volume be if the
pressure were increased to 2.4 atm?

Plan
We know the volume at one pressure and want to find the volume at another pressure (constant
temperature). This suggests that we use Boyle’s Law. We tabulate what is known and what is
asked for, and then solve the Boyle’s Law equation for the unknown quantity, V 2.

Solution

We have

V 1 12 L P 1 1.2 atm

V 2 _?_ P 2 2.4 atm

Solving Boyle’s Law, P 1 V 1 P 2 V 2 , for V 2 and substituting gives

V 2 6.0 L

(1.2 atm)(12 L)



2.4 atm

P 1 V 1



P 2

Pressure and volume are inversely

proportional. Doubling the pressure

halves the volume of a sample of gas at

constant temperature.

It is often helpful to tabulate what is

given and what is asked for in a

problem.

12-4 Boyle’s Law: The Volume–Pressure Relationship 443

EXAMPLE 12-2 Boyle’s Law Calculation

A sample of oxygen occupies 10.0 L under a pressure of 790. torr (105 kPa). At what pressure
would it occupy 13.4 L if the temperature did not change?

Plan

We know the pressure at one volume and wish to find the pressure at another volume (at
constant temperature). We can solve Boyle’s Law for the second pressure and substitute.

Solution

We have P 1 790. torr; V 1 10.0 L; P 2 ?; V 2 13.4 L. Solving Boyle’s Law, P 1 V 1 P 2 V 2 ,
for P 2 and substituting yields

P 2 590. torr
78.6 kPa

You should now work Exercises 16 and 17.

101.3 kPa



760. torr

(790. torr)(10.0 L)



13.4 L

P 1 V 1



V 2

Problem-Solving Tip:Units in Boyle’s Law Calculations

Which units for volume and pressure are appropriate for Boyle’s Law calculations? Boyle’s

Law in the form P 1 V 1 P 2 V 2 can be written as V 1 /V 2 P 2 /P 1. This involves a ratio of

volumes, so they can be expressed in any volume units—liters, milliliters, cubic feet—

as long as the sameunits are used for both volumes. Likewise, because Boyle’s Law

involves a ratio of pressures, you can use any units for pressures—atmospheres, torr,

pascals—as long as the sameunits are used for both pressures.