Boyle’s Law
This is the first of the five-odd gas laws you’ll need
to know for the SAT II Chemistry test. Study these laws closely
because you are sure to see a question or two that asks you to apply
them.
Boyle’s law simply states that the volume
of a confined gas at a fixed temperature is inversely proportional
to the pressure exerted on the gas. This can also be expressed as PV =
a constant. This makes sense if you think of a balloon. When the
pressure around a balloon increases, the volume of the balloon decreases,
and likewise, when you decrease the pressure around 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 a component
of car exhaust and power plant discharge, and it plays a major role
in the formation of acid rain. Consider a 3.0 L sample of gaseous
SO2 at a pressure of 1.0 atm. If the pressure
is changed to 1.5 atm at a constant temperature, what will be the
new volume 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.
