1. The problem statement, all variables and given/known data If 0.8kg of water at 100 celsius is mixed with 0.8kg of water at 0 celsius, is this process reversible? 2. Relevant equations Entropy: S = mcln(T_2/T_1) 3. The attempt at a solution I've already calculated the entropy of the process, which is 81.1 J/K. But how do I know if it's reversible?