Bob adds heat to a liquid substance. When enough heat is added, the liquid would undergo a phase transition from the liquid to the vapor phase. This process is called evaporation. It is an endothermic process where heat should be supplied to the system for the process to happen. The temperature of the system, when enough heat is supplied to allow phase transition, is called the boiling point. It is the temperature when the substance starts to boil in turn to a gas or a vapor. The heat that is associated during boiling is called the latent heat of vaporization. It is the heat that is absorbed during the phase change without changing the temperature of the system.
