This is the first of the five-odd gas laws you’ll need to know forthe
SAT II Chemistry test. Study these laws closely because you aresure to see a question or two that asks you to apply them.
Boyle’s law simply states that thevolume of a confined gas at a fixed temperature is inverselyproportional to the pressure exerted on the gas. This can also beexpressed as
PV = a constant. This makes sense if you think ofa balloon. When the pressure around a balloon increases, the volume ofthe balloon decreases, and likewise, when you decrease the pressurearound a balloon, its volume will increase.
Boyle’s law to can also be expressed in the following way, and this is the form of the law that you should memorize:
P1V1 = P2V2
Example
Sulfur dioxide (SO2) gas is acomponent of car exhaust and power plant discharge, and it plays amajor role in the formation of acid rain. Consider a 3.0 L sample ofgaseous SO2 at a pressure of 1.0 atm. If the pressure ischanged to 1.5 atm at a constant temperature, what will be the newvolume of the gas?
Explanation
If
P1V1 =
P2V2, then (1.0 atm) (3.0 L) = (1.5 atm) (
V2), so
V2 = 2.0 L. This answer makes sense according to Boyle’s law—as the pressure of the system increases, the volume should decrease.
