Question

Explain why, to maximize entropy, ice must remain at 0 degrees Celsius until all of it melts?

Answer 1

When thermal energy is added to solid ice, it melts from ice at zero degrees Celsius into liquid water that is also at zero degrees Celsius. When the liquid water is further heated it can evaporate, becoming a gas, water vapor. The more thermal energy a molecule has, the faster it moves and the more disordered the motion of a collection of such molecules becomes. In other words, as the thermal energy of the system of molecules increases (solid to liquid to gas), there is a progression from less disordered to more disordered behavior, that is, from a lower entropy state to a higher entropy state.

The entropy of a physical system left to itself will increase or, if the system is already at its maximum entropy, the entropy will remain the same.