Where does the Kinetic energy of the expantion of freezing ice come from? For example, say you had a gram of water inside a piston. The water freezes and the expantion of ice pushes the piston up. Since the heat of fusion of water is 80 calories per gram, lets say to initally melt that ice to water I had to apply 80 calories of heat to get the water to it's liquid form. Now when the ice is freezing, does it give off that same 80 calories of energy in the form of heat? Or is some of that energy transformed into mechanical energy to push the piston up?