Are the following changes reversible or irreversible? Give proper explanations: (i) Melting of ice at `0^(@)C` and 1 atm pressure (ii) The pressure of a gas enclosed in a cylinder fitted with a piston is 5 atm. The gas is expanded against an external pressure of 1 atm.

Explanation

(i) At `0^(@)C and 1` atm pressure ice remains in equilibrium with water. If the temperature of the sytem is increased by ann infinitesimal amount, ice melts into water slowly. Again, if the temperature of the system is decreased by an infinitesimal amount, water freezes into ice slowly. thus, an infinitesimal increase or decrease in temperature causes the change in the direction of the process. hence, the melting of ice at `0^(@)C` and 1 atm pressure can be considered as a reversible process. (ii) An irreversible process: The external pressure is considerable less than the pressure of the gas, so, the gas will expand rapidly without maintaining thermodynamic equilibrium during the process. hence, this expansion will occur irreversibly.