Why are most natural processes irreversible?
**Reversibility** reversible process can be reversed by infinitesimal change, no entropy production, quasi-static without friction, e.g., Carnot cycle reversible, irreversible processes involve friction, free expansion, heat transfer across finite temperature difference, entropy increases, most real processes irreversible. Most natural processes involve dissipative effects (e.g., friction, viscosity) or occur through non-equilibrium states (e.g., free expansion), preventing the system and surroundings from returning to their original states without external intervention. Using first law ΔU = Q
Ref: NCERT > Physics Book > Thermodynamics > Cyclic Processes and Reversibility Concepts