Why is it impossible to superheat steam in the presence of boiling water?

The reason it is impossible to superheat steam in the presence of boiling water is that all the added heat is used to convert additional boiling water into steam rather than increasing the temperature of the existing steam.

When water is at boiling point, any heat supplied to the system is directed towards the phase change from liquid to vapor. This means that instead of raising the temperature of steam above the saturation point, the energy input facilitates the transition of more water molecules into the vapor state. This process keeps the temperature of the saturated steam constant at the boiling point corresponding to that specific pressure.

This principle is crucial in thermodynamics, where the treatment of phase changes is distinctly recognized; the temperature of steam remains stable during the boiling process as it absorbs heat until all the liquid has turned into vapor. Therefore, the presence of boiling water acts as a natural limit to how much the steam can be superheated, as the focus of heating is on producing more steam from liquid water rather than changing the temperature of steam already present in the system.