Hello!
When heat is removed from a substance, the kinetic energy of the molecules decreases (the molecules start to move more slowly).
The changes are caused by the tendency of the system to reach equilibrium and when the surroundings of the substance have lower kinetic energy, heat is transferred to reach thermodynamic equilibrium.
What's happening in whole is that there is a temperature gradient (difference) between the substance and its surroundings, and for eliminating this gradient, heat flows from the hotter substance to the colder surroundings, for them to have the same temperature.
The temperature of the substance decreases because its molecules have lower kinetic energy.
Have a nice day!
