Question

Which of the following process is quasi static process?
1. Ideal iso-thermal process
2. Ideal iso-baric process
3. Ideal adiabatic process
4. All of these

Answer 1

Correct Answer - Option 4 : All of these

CONCEPT:

Reversible processes:

• A thermodynamic process is reversible if the process can be turned back such that both the system and the surroundings return to their original states, with no other change anywhere else in the universe.
• From the preceding discussion, a reversible process is an idealized notion.
• A process is reversible only if:
  1. It is quasi-static (system in equilibrium with the surroundings at every stage).
  2. There are no dissipative effects.
• Example:
  • ​A quasi-static isothermal expansion of an ideal gas in a cylinder fitted with a frictionless movable piston is a reversible process.
  • Frictionless pendulum

Irreversible processes:

• If a thermodynamic process cannot be turned back such that both the system and the surroundings return to their original states, with no other change anywhere else in the universe, then the process is irreversible.
• Irreversibility arises mainly from two causes:
  1. Many processes (like a free expansion, or an explosive chemical reaction) take the system to non-equilibrium states.
  2. Most processes involve friction, viscosity, and other dissipative effects.
• Since dissipative effects are present everywhere and can be minimized but not fully eliminated, most processes that we deal with are irreversible.
• Example:
  • A moving body coming to a stop and losing its mechanical energy as heat to the floor and the body.
  • A rotating blade in a liquid coming to a stop due to viscosity and losing its mechanical energy with a corresponding gain in the internal energy of the liquid).
  • Heat transfer by conduction, convection, and radiation.

EXPLANATION:

• We know that for an ideal thermodynamic process the system remains in equilibrium with the surroundings at every stage.
• Hence, option 4 is correct.

Important points related to irreversibility:

• As we have seen, one of the concerns of thermodynamics is the efficiency with which heat can be converted into work.
• The Second Law of Thermodynamics rules out the possibility of a perfect heat engine with 100% efficiency.
• It turns out that a heat engine based on idealized reversible processes achieves the highest efficiency possible.
• All other engines involving irreversibility in any way (as would be the case for practical engines) have lower than this limiting efficiency.