Which among the following is NOT the feature of reversible process?
Which among the following is NOT the feature of reversible process?
The driving and opposing forces differ by large amount.
The process can be reversed by infinitesimal change in pressure.
A reversible process proceeds very slowly.
The system attains mechanical equilibrium at the end of every step.
Solution
The correct answer is Option A, "The driving and opposing forces differ by large amount." To understand why, let's explore each option in relation to the characteristics of a reversible process:
Option A: The driving and opposing forces differ by large amount.
This is NOT a feature of a reversible process. In a reversible process, the change occurs in such a manner that the system and surroundings can be returned to their original states by exactly reversing the change. For this to happen, the driving force (such as pressure or temperature causing the change) must differ from the opposing force by an infinitesimally small amount, not a large one. This way, the system can always be in a state of equilibrium, or near equilibrium, with its surroundings.
Option B: The process can be reversed by infinitesimal change in pressure.
This is a feature of a reversible process. Since a reversible process is always close to equilibrium, only an infinitesimally small deviation is needed to reverse the direction of the process, whether it be a change in pressure, volume, or any other thermodynamic variable.
Option C: A reversible process proceeds very slowly.
This is also a feature of a reversible process. The process must proceed at an infinitely slow rate to ensure that the system undergoes a series of equilibrium states. This slow progression means that the system has time to adjust to virtually indistinguishable changes in the external conditions.
Option D: The system attains mechanical equilibrium at the end of every step.
This is another characteristic of a reversible process. Because the process happens so slowly and the driving forces are matched very closely by the opposing forces, the system can be said to be continually in mechanical (as well as thermal and chemical) equilibrium at each stage of the process.
Thus, the option that does not describe a reversible process is Option A, as a large difference between driving and opposing forces would lead to an irreversible process, where the system cannot be returned to its original state without causing changes in the surroundings.