When water freezes to form ice, the molecules would be vibrating in place rather than moving round. It is a result of a decrease in the kinetic energy of the molecules of water. It is said that the temperature and the kinetic energy of the molecules is directly proportional which means that when temperature is increased, the kinetic energy of the molecules would increase as well making the molecules move around. However for this case, when we day the system is cooled then it means the temperature is decreased which would result to the decrease of the kinetic energy of the molecules.