In a process, the total entropy of the universe must increase for a process to be spontaneous. Which option expresses this principle?

In a process, the total entropy of the universe must increase for a process to be spontaneous. Which option expresses this principle?

• A. Total entropy of universe must increase.
• B. Total energy must decrease.
• C. System entropy must increase only.
• D. The surroundings must cool.

Answer: (A)

Spontaneity is guided by the second law: the entropy of the universe must increase for a process to occur on its own. This means the total entropy change, adding together the system and its surroundings, must be positive: ΔS_universe = ΔS_system + ΔS_surroundings > 0. The system’s entropy can go up or down, but as long as the surroundings gain enough entropy (for example, by releasing heat to them in an exothermic process), the overall entropy increases and the process is spontaneous. That’s why the statement that the total entropy of the universe must increase best expresses the principle. The other ideas don’t fit universally: spontaneity isn’t determined solely by a decrease in energy; the system’s entropy alone isn’t the whole story since the surroundings contribute as well; and the surroundings do not have to cool—heat flow can either raise or lower the surroundings’ temperature, but what matters is the net increase in total entropy.

Spontaneity is guided by the second law: the entropy of the universe must increase for a process to occur on its own. This means the total entropy change, adding together the system and its surroundings, must be positive: ΔS_universe = ΔS_system + ΔS_surroundings > 0. The system’s entropy can go up or down, but as long as the surroundings gain enough entropy (for example, by releasing heat to them in an exothermic process), the overall entropy increases and the process is spontaneous. That’s why the statement that the total entropy of the universe must increase best expresses the principle. The other ideas don’t fit universally: spontaneity isn’t determined solely by a decrease in energy; the system’s entropy alone isn’t the whole story since the surroundings contribute as well; and the surroundings do not have to cool—heat flow can either raise or lower the surroundings’ temperature, but what matters is the net increase in total entropy.