As you add energy to the ice the random vibrations of the ice molecules increase as the temperature rises. Ice is at first in the form of a lattice structure as seen below. As seen the ice has very little movement and forms a solid structure.





As the molecules move so quickly that they break apart and form water. This occurs at the melting point, seen at the first plateau of the heating curve above. At this point all the energy added to the system goes to breaking the ice structure and NO temperature change occurs until all the ice is completely gone.

At this point the molecules are at a liquid phase. Unlike the ice phase, the molecules in the liquid are not in a set lattice energy but instead have some movement. This can be seen by this short short animation. (from the Chemist Art Gallery found at www.csc.fi)


After all the ice is gone and the substance is completely liquid it begins to heat up again. At 100º Celsius the liquid begins to form a gas, seen by the second plateau on the heating curve. Again all energy that is put into the system does not influence the temperature until all liquid is gone and the substance is entirely gaseous.

In the gas state the molecules of the substance move around rapidly, much different from the liquid and ice phase. None of the molecules are even touching each other. Below is a picture of gas particles on a 3-dimensional plane. Note the distance between the molecules.








For the cooling of a substance the graph is entirely the same, exact that it is opposite. The process is seen as the cooling curve, also called the solidification curve.