Question

The cause of irreversibility of a natural process is:
A. A process can take a system to a non-equilibrium state.
B. A process often involves dissipative effects.
C. Both a) and b)
D. None of the above

Answer 1

Hint: Irreversible process is a process in which both the system and surround cannot be converted to its initial state. All microscopic natural processes are irreversible. It is due to the reason that there is a difference between the entropy at the initial and the final state of the process. This can be explained by the second law of thermodynamics.

Complete answer:
Entropy is a state function, the total entropy of the system is the same for all processes (reversible or irreversible). The second law of thermodynamics is used to determine whether a process is reversible or irreversible. All complex microscopic natural processes are irreversible.

2nd Law of thermodynamics states that:
The total entropy of an isolated system never changes with time, and it is possible only if all processes are reversible. Isolated systems spontaneously move toward the thermodynamic equilibrium state, which is the state with highest entropy.

Mathematical expression:
The second law states that there exists a state variable named as entropy denoted by S. The change in entropy ($\Delta S$) is equal to the heat transfer ($\Delta Q$) by the temperature ( T).
\[\Delta S=\dfrac{\Delta Q}{T}\]

The natural process that starts in one equilibrium state and ends in another will go in the direction that causes the entropy of the system plus the environment to increase for an irreversible process.
\[S_{f} > S_{i}\]
By this we come to a conclusion that natural processes are irreversible because a process can take a system to a non-equilibrium state, and a process often involves dissipative effects.

So, the correct answer is “Option C”.

Note:
Read the question and all the options carefully before concluding an answer. The total entropy of the closed system will always be constant but the initial and final state of the system will not remain the same if all the physical properties remain the same.