Question

During the heating of naphthalene, the temperature of it stays constant for a period of time. Why the temperature of naphthalene stayed constant?

Answer 1

Assuming solid naphthalene is heated.

Naphthalene is heated till it reaches its melting point just as the solid begins to melt, it will stay at that temperature until all the molecules in it have absorbed enough kinetic energy to break the bonds keeping it in solid state.

As soon as it has absorbed enough heat to change its state, it changes its state to its liquid form and begins to increase its temperature normally as heat is added.