what happens to the volume of a substance when the temperature increases?:
If the pressure of a gas is held constant, its volume is proportional to the temperature. As the temperature increases, the atoms move faster and require more space so that they strike the walls of the container with the same net force. The volume increases. If the temperature of a gas is held constant, its pressure is inversely proportional to the volume. If the volume of a gas is decreased, then the same number of atoms moving at the same speed (because the temperature has not changed) will strike the walls of the container more often.