The answer
In an irreversible process, entropy increases because the system moves from a state of lower probability to higher probability. Irreversibility means some energy becomes unavailable to do work, often as heat, due to factors like friction, turbulence, or spontaneous mixing. The second law states that total entropy of an isolated system never decreases. In irreversible processes, the final state has more possible microstates, so entropy (a measure of disorder) increases. For example, when a hot body cools, heat spreads out, increasing randomness. Reversible processes keep entropy constant because they happen in infinitesimal steps, but irreversible ones have a net increase in total entropy.
