Question

Which of the following best describes the second law of thermodynamics?

• A. Energy can neither be created nor destroyed
• B. At absolute temperature, the entropy of a perfect crystal is zero
• C. When an isolated system undergoes a spontaneous change, the entropy of the system will increase.
• D. The internal energy of the universe is constant

Answer 1

The correct option is C

When an isolated system undergoes a spontaneous change, the entropy of the system will increase.

Explanation for correct option:

Option (C):

1. Entropy is a measure of disorder and according to the second law of thermodynamics, the change in the total entropy of a system will either be positive or zero. It can never be negative.
2. This tells us the direction in which a thermodynamic process may occur.

Explanation for incorrect options:

Option (A): The given statement is that of the conservation of energy. It can be used to describe the first law of thermodynamics and not the second.

Option (B): The third law of thermodynamics tells us that the entropy of a perfect crystal at $0\mathrm{K}$, is zero.

Option (D): The internal energy is the total energy associated with the disorder of particles in a system. The statement has no relation to the second law of thermodynamics.

Hence, the correct answer is option (C).