13. Adding thermal energy to a gas at constant

pressure will cause

It will increase the kinetic energy of gas particles and hence gas will expand.

Explanation:

According to law, there is direct relationship between temperature (thermal energy) of gas and it's volume. When the pressure of gas is held constant and it's temperature increases then the volume of gas also gets increases.

When the temperature (thermal energy) of gas increases then the kinetic energy of particles of gas also gets increases due to which particles start to collide with the wall of container and with themselves as well which in turn causes gas to expand.