Seems like there is this new type of heat in town.
Temperature is just the average kinetic energy; heat is basically movement of particles, so basically kinetic energy, so temperature is the measure of heat?
My teacher told me that the heat energy is converted to kinetic energy, so there is no change in temperature. But heat energy is basically kinetic energy, and temperature is the measure of kinetic energy. Maybe my understanding of latent heat isn't crisp, if so please explain it to me.
Best Answer
Thermal energy is not basically kinetic energy. Thermal energy includes molecular level translational and rotational modes, which are purely kinetic, but it also includes vibrational, torsional, and electronic modes which include potential energy as well. The average thermal energy is the same in all of these modes at thermal equilibrium. Temperature is proportional to the average energy per mode, regardless of whether the energy in a mode is kinetic, potential, or a mix.
The idea that thermal energy is kinetic energy stems from studying ideal gasses, where there are no other internal modes. But not all materials are ideal gasses, particularly not when a system is undergoing a phase change. Do not over-generalize what you learned from ideal gasses.
In latent heat, what is happening is that more of these internal modes are being recruited. As additional thermal energy is added it is not going into increasing the average energy in each mode, but it is instead going into increasing the number of modes that contain the same average energy. For example, in melting, there are vibrational modes in the solid and in the liquid there are also translational modes. As latent heat is added more of the molecules excite the translational modes, corresponding to the change from solid to liquid at a fixed temperature.