Which statement about entropy reflects the Second Law as described?

Which statement about entropy reflects the Second Law as described?

• A. The entropy of a perfectly crystalline substance at absolute zero is finite.
• B. Entropy measures the average kinetic energy of molecules.
• C. The total entropy of the universe never decreases.
• D. Entropy is conserved in all mechanical processes.

Answer: (C)

Entropy is a measure of how many microscopic configurations a system can have for a given macroscopic state. The Second Law says that, for any natural, spontaneous process, the total entropy of an isolated system cannot decrease; for the universe as a whole, entropy can only increase or stay the same. The statement that the total entropy of the universe never decreases captures this universal tendency. Why the other ideas don’t fit: entropy is not a measure of average kinetic energy—that’s what temperature relates to. A perfect crystal at absolute zero has zero entropy, not finite entropy, by the relevant thermodynamic principle. And entropy is not conserved in all mechanical processes; irreversible processes increase entropy, while only idealized reversible processes can keep entropy constant.

Entropy is a measure of how many microscopic configurations a system can have for a given macroscopic state. The Second Law says that, for any natural, spontaneous process, the total entropy of an isolated system cannot decrease; for the universe as a whole, entropy can only increase or stay the same. The statement that the total entropy of the universe never decreases captures this universal tendency.

Why the other ideas don’t fit: entropy is not a measure of average kinetic energy—that’s what temperature relates to. A perfect crystal at absolute zero has zero entropy, not finite entropy, by the relevant thermodynamic principle. And entropy is not conserved in all mechanical processes; irreversible processes increase entropy, while only idealized reversible processes can keep entropy constant.