Answer to Question #56683 in General Chemistry for anna

Question

Why does a liquid at boiling point remain the same temperature until it is all converted to a gas?

Answer 1

When the liquid is heated, heat absorbed by the system increases the kinetic energy of the molecules. This energy increase is what we can observe is the increase in temperature. The temperature goes up until the boiling point. It is the point when the molecules acquire enough energy to overcome te forces that keep them together in the liquid phase. When this happens, the molecules, which transfer to the gas phase take some energy from the liquid. So that in order to evaporate other amount of molecules the system needs more energy. That is why during additional system heating the temperature keeps constant until all the liquid is being evaporated.