Write a short note on reversible and irreversible processes.

(N/A) process is said to be reversible if it can be retraced in the opposite direction such that both the system and the surroundings return to their original states without leaving any net change in the universe. Reversible processes are ideal and cannot be fully realized in practice.
An irreversible process is one that cannot be reversed to restore the system and surroundings to their initial states. Most natural processes are irreversible. Examples include:
$(1)$ Heat transfer from a hot body to a cold body.
$(2)$ Diffusion of gases.
$(3)$ Combustion of fuel.
$(4)$ Rusting of iron.
$(5)$ Friction and viscosity effects.
Irreversibility arises primarily due to:
$(i)$ The system passing through non-equilibrium states during the process.
$(ii)$ The presence of dissipative effects like friction and viscosity,which cannot be completely eliminated.