Which of the following is not a reversible process ?
A. Expansion of an ideal gas against constant pressure
B. Atmospheric pressure vaporisation of water at 100°C
C. Solution of NaCl in water at 50°C
D. None of these
Answer: Option C
Solution (By Examveda Team)
Since the entropy of mixing is positive we can say the mixing process or solution formation process is an irreversible process.This Question Belongs to Chemical Engineering >> Chemical Engineering Thermodynamics
Let's carefully analyze each option to determine which process is not reversible:
🔹 A. Expansion of an ideal gas against constant pressure
This involves expansion against a finite external pressure.
For a process to be reversible, the driving force (like pressure difference) must be infinitesimally small.
Expansion against constant pressure is a classic example of an irreversible process.
✅ This is NOT a reversible process.
🔹 B. Atmospheric pressure vaporisation of water at 100°C
At 100°C and 1 atm, water boils at equilibrium.
If done infinitely slowly, this can be reversible (e.g., in a reversible Carnot engine).
✅ This can be reversible.
🔹 C. Solution of NaCl in water at 50°C
The dissolution of NaCl can be modeled as a reversible process under ideal and equilibrium conditions.
✅ This can be reversible.
🔹 D. None of these
This would be correct only if all options were reversible.
But A is definitely not reversible.
✅ Correct answer: A. Expansion of an ideal gas against constant pressure