Reversible Process
- A reversible process is an ideal, perfectly efficient process that happens so slowly and smoothly that the system is always in equilibrium with its surroundings.
- It can be reversed by making an infinitesimally small change, with no loss of energy as heat or work.
- No entropy is generated in a reversible process.
Examples:
- Isothermal expansion of a gas done infinitely slowly.
- Slow, frictionless piston movement in an engine.
Irreversible Process
- An irreversible process is what actually happens in real life. It is fast, involves friction, unrestrained expansion, mixing, or heat transfer with a finite temperature difference.
- It cannot be reversed exactly to restore both the system and surroundings to their original state.
- Entropy is always produced in irreversible processes.
Examples:
- Free expansion of gas into a vacuum.
- Real combustion in engines.
- Heat flow from a hot body to a cold one.
Key Difference in One Line
- Reversible process: Ideal, no entropy production, maximum efficiency.
- Irreversible process: Real, entropy increases, less efficient.