What happens to the temperature and thermal energy of a substance during a change of state?
During a change of state, such as melting, freezing, vaporization, or condensation, the temperature of a substance remains constant, while the thermal energy of the substance increases or decreases, depending on the direction of the change. For example, when a solid is heated, its temperature will increase until it reaches its melting point. At that point, the solid will begin to melt, but its temperature will remain constant until all of the solid has been converted to liquid. This is because the energy that is being added to the system is being used to break the bonds between the particles of the solid, rather than to increase the temperature of the substance. Once all of the solid has been converted to liquid, any additional energy that is added to the system will cause the temperature of the liquid to increase. Similarly, when a liquid is cooled, its temperature will decrease until it reaches its freezing point. At that point, the liquid will begin to freeze, but its temperat...