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**Entropy related questions -- Reversible or Irreversible?**

## Homework Statement

A 15.0kg block of ice at 0C melts to liquid water at 0C inside a large room that has a temperature of 20C. Treat the ice and the room as an isolated system, assume that the room is large enough for its temperature change to be ignored. a) Is the melting of the ice reversible or irreversible? Explain, using simple physical reasoning without resorting to any equations.

b) Find the net entropy change of the system during this process. Explain whether or not this result is consistent with your answer to part a.

## The Attempt at a Solution

I initially said the process is reversible because it stays in thermal equilibrium (0C), but the answer key says it's irreversible. As for the entropy I got 1253J/K which is the right answer.

Could someone please explain to me the theory behind entropy and reversible/irreversible processes?

Thanks!