Molecular movement depends on the applied temperature. Suppose that you have liquid water in a boiler. Half of it is
liquid and the other half is gas. They are in equilibrium. If you heat the
liquid water, the molecules in the liquid water tend to separate from its
neighboring molecules and go into the gaseous phase of water. The liquid in
water has higher pressure and greater volume. More molecules of liquid water
will enter into the gaseous phase. There will now be more molecules of water in
the hotter air because it has greater volume (the distances between the
particles is high) and faster molecules tend to go in the gas. Also, its
kinetic energy is high due to the increase in temperature. However, when it is
in colder air, the kinetic energy of the molecules is low because the
temperature is low.
