Question

Why does the temperature of a substance remain constant during a phase change?

Answer 1

The temperature of any substance is related to its average kinetic energy where energy is the ability to do work. When a solid is heated, the average kinetic energy of the substance increases because of which the temperature increases. But during phase change the energy given or taken in is called latent heat which is used only to form bonds between molecules or break the bonds between molecules. This heat won’t affect the average kinetic energy of the substance.  

Since average kinetic energy of the substance will remain same during phase change, the temperature will remain same too.