Can you please help me figure out why evaporation is a cooling process and why becoming a solid is a heating process?
evaporation absorbs heat from the environment, thus "cooling" the environment.
becoming solid is a heating process as heat is moved from the mass being solidified to the environment. The environment is getting the heat.
We could go through a long explanation about kinetic energy and how it takes energy to make the molecules of a liquid become a gas. The energy must come from somewhere and that place is the liquid. However, I personally, like to write this simple equation.
We know that we must ADD heat to make water turn to vapor.
H2O(l) + heat ==> H2O(g)
We can add the heat with a burner to help it along, OR we can let nature do it. If nature does it, the heat must come from some place, and that is the liquid. It's an endothermic process.
Crystallization, however, is an exothermic process. Here is the equation.
H2O(s) + heat ==> H2O(l) OR
ice + heat ==> melts to liquid
So if we must ADD heat to melt ice, which we know we must do, then the reverse of that (liquid to ice) MUST give off heat (exothermic). I hope this helps.