I am looking into whether the melting of ice (or any substance for that matter) at constant pressure and temperature is reversible or irreversible. Different sources say different things, and it may well depend on specific conditions. But is it generally said that melting is reversible or irreversible?
[Physics] Melting ice: reversible or irreversible
icephase-transitionreversibilitythermodynamicswater
Best Answer
To cause a phase change from a solid to a liquid (melting of ice) heat is required. That requires exposure of the solid to an environment whose temperature is greater than the solid. Heat transfer over a finite temperature difference is irreversible.
However, the process can theoretically be made reversible if the temperature difference is infinitesimal. Problem is the rate of heat transfer is proportional to the temperature difference (for conduction and convection) or proportional to the difference in the temperatures to the fourth power (for radiation). That would make the time to melt infinite for a reversible process.
All reversible processes are idealizations. All real processes are irreversible. Perhaps this is one of the reasons you find "different sources say different things".
Hope this helps.