twice the volume in which to move around. Thus, gas molecules will hit the
container walls less often, exerting half as much pressure.
When there’s no change in temperature, volume and pressure are inversely
proportional. Triple the volume, and you’ll cut the pressure to one-third of its
original value. Cut the volume by one-half, and you’ll double the pressure.
The mathematical formula which relates pressure and volume while temperature
is held constant is called Boyle’s Law, and is represented by = . The
units of pressure and volume don’t matter, as long as they are consistent across
both sides of the equation.
Temperature and Volume Now suppose we start with the same 3 L sample of
gas at 200 K and 900 torr. If, without changing the pressure, we were to increase
the temperature to 400 K, what would happen to the volume? Well, if the gas
molecules are moving faster, they are going to spread out further, effectively
doubling the volume of the container. You can test this yourself; if you put a
balloon in the freezer (lowering the temperature of the gas inside), the balloon
will shrink. If you leave the balloon outside on a hot summer day, the balloon
will expand.
When there’s no change in pressure, temperature and volume are directly
proportional. This is mathematically represented by Charles’ Law:
=
While the units of volume don’t matter as long as they are consistent across both
sides of the equation, temperature must be measured in Kelvins in order to use
this law.