Barrons SAT Subject Test Chemistry, 13th Edition

set of conditions, the terms on the right side of the equation are equal to the same
constant, so P 1 V 1 = P 2 V 2. This matches the Boyle’s Law equation introduced

earlier.
The same can also be done with Charles’s Law, because PV = nRT can be
expressed with the variables on the left and the constants on the right:

In Charles’s Law the number of moles and the pressure are constant.

Substituting k for the constant term, , we have

The expression relating two sets of conditions can be written as

TIP

Know the ideal gas constant:

To use the Ideal Gas Law in the form PV = nRT, the gas constant, R, must be
determined. This can be done mathematically as shown in the following example.
One mole of oxygen gas was collected in the laboratory at a temperature of
24.0°C and a pressure of exactly 1 atmosphere. The volume was 24.38 liters.
Find the value of R.

PV = nRT

Rearranging the equation to solve for R gives

Substituting the known values on the right, we have

Calculating R, we get