Which statement about entropy in a closed system is true?

Which statement about entropy in a closed system is true?

• A. Entropy always decreases in spontaneous processes.
• B. Entropy cannot be measured.
• C. Entropy is negative for all systems.
• D. The total entropy of a system plus its surroundings never decreases.

Answer: (D)

Entropy tends to increase as natural processes unfold. When you consider a system together with its surroundings, the total entropy cannot decrease; it stays the same for a perfectly reversible process and increases for an irreversible one. This is the second law in action. A simple way to see it is a hot object cooling in a room: the object’s entropy drops as it loses heat, but the surroundings gain more entropy from the absorbed heat, so the overall entropy increases. The idea that total entropy never decreases captures why spontaneous processes don’t run in reverse on the whole universe. Entropy can be measured and quantified, so the claim that it cannot be measured isn’t right. Entropy isn’t negative for all systems; it’s a measure of the number of microscopic configurations and is typically positive, with zero at absolute zero for a perfectly crystalline ground state. And the notion that entropy always decreases in spontaneous processes contradicts the second law, which allows for a decrease in a specific part of the system only if the surroundings’ entropy increases by at least as much.

Entropy tends to increase as natural processes unfold. When you consider a system together with its surroundings, the total entropy cannot decrease; it stays the same for a perfectly reversible process and increases for an irreversible one. This is the second law in action. A simple way to see it is a hot object cooling in a room: the object’s entropy drops as it loses heat, but the surroundings gain more entropy from the absorbed heat, so the overall entropy increases. The idea that total entropy never decreases captures why spontaneous processes don’t run in reverse on the whole universe.

Entropy can be measured and quantified, so the claim that it cannot be measured isn’t right. Entropy isn’t negative for all systems; it’s a measure of the number of microscopic configurations and is typically positive, with zero at absolute zero for a perfectly crystalline ground state. And the notion that entropy always decreases in spontaneous processes contradicts the second law, which allows for a decrease in a specific part of the system only if the surroundings’ entropy increases by at least as much.