1. The problem statement, all variables and given/known data A ball of ice is thrown against a wall with such as speed than the ball of ice evaporates. Is this process reversible? 2. Relevant equations if entropy doesn't change, process is reversible. 3. The attempt at a solution I'm pretty darn sure the answer is no, but I am looking for qualitative reasons as to why this is not reversible. When my teacher went over reversibility, he said we should just run the process in (time) reverse and see if it makes sense. This situation does not make sense to me in reverse; water vapor will not spontaneously condense and freeze into an ice-ball that has some velocity. Can anyone offer a more concrete line of reasoning other than "this process doesnt make sense in reverse".