Question #84bc6
1 Answer
Good question.
What we perceive as heat is really the kinetic energy of atoms and molecules. That is, heat is a function of how fast atoms and molecules are moving. The hotter it gets, the faster atoms and molecules move!
Even in a solid, the atoms and molecules of a substance are moving very tiny distances, vibrating within the matrix they are locked in to. That brings up the question, "why are these atoms and molecules locked in to a matrix?" That is because, whatever intermolecular or interatomic forces bind a solid together are stronger than the forces that want to pull the solid apart (at the atomic/molecular level).
However, as the temperature increases, the atoms and molecules begin to vibrate with such force that they can slip and slide past each other. Make no mistake, the forces binding the atoms and molecules together are still present, but now the thermal energy of the atoms and molecules is enough to somewhat off-set that. Atoms and molecules begin to shuffle around. When the atoms and molecules are still bound to each other but are free to move past each other we call that a liquid.
As the heat continues to rise, the energy available to an individual atom or molecule (gained from colliding with its neighbors) becomes enough to completely overcome the forces that were holding the substance together! The atoms and molecules break free of the liquid (or, in the case of carbon dioxide go directly from a rigid solid--this is called sublimation) to become a gas.
The reverse of the process, cooling, is a mirror image of the steps we have talked about above with the gas molecules or atoms first cooling enough that the forces between them start to cause them to stick together in a liquid and eventually as cooling continues, force the liquid atoms or molecules to lock up in a rigid structure, a solid.
Cool, eh?
