Phase Changes - Phase change operations must also be presented in order to fully understand heat transfer systems. It is common knowledge that materials change from solid to liquid and from liquid to gas at certain temperatures. However, simply supplying enough energy to reach that temperature is not sufficient to cause a phase change. Consider a block of ice. As heat is added to the block of ice, the temperature of the ice will rise to the melting point. At this temperature, additional heat added will not increase the temperature, but will instead enable the water to shift from solid to liquid phase. The temperature will remain at this point until all of the ice is melted, and then it will begin to increase as heat continues to be added. The amount of energy required for this phase change is referred to as the latent heat of fusion. A similar heat of vaporization exists for the phase change from a liquid to a gas.