Question

WILL FAN AND MEDAL

when heat is added to a substance, describe how the molecules are affected

if you can, please use the works kinetic energy and potential energy.

Answer 1

"When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space."

Answer 2

Somehow or other, when heat is transferred to a body, the kinetic energy of the atoms/molecules increases. Since kinetic energy is given by the formula \[KE=\frac{ 1 }{2 }mv ^{2}\] and since the mass of the molecules doesn't change (not here, at least ... it does change in the relativistic case) then the speed, v, of the molecules/atoms does change. It increases. The speed can manifest itself as a change in frequency of the molecules if they are oscillating, or simply an increase in the pressure of the substance. The substance then pushes on its boundaries, and gives rise to what we see as thermal expansion, either through the gas laws for gases, or linear expansion for solids.
The way that this question if phrased here is actually pretty vague.The answer in one sentence would be, for me at least, "the molecules move faster". But, the "master" that set this question would probably give me a dirty look.
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Answer 3

If there is no change of state then the kinetic energy of the molecules will increase (the temperature increases) as will the separation of the molecules (the material will expand). Increasing the separation of the molecules will also increase their potential energy.

If there is a change of state the kinetic energy of the molecules does not change but their potential energy will increase (bonds between the molecules will be broken).