True or false: the second law of thermodynamics says that the entropy of a system cannot spontancously decrease.

It is true only if we consider an isolated system

Explanation:

The second law of thermodynamics requires that, in general, the total entropy of any system cannot be reduced except by increasing the entropy of some other system. Therefore, in a system isolated from its surroundings, the entropy of that system tends not to diminish. It follows that heat cannot flow from a colder body to a warmer body without the application of work (the imposition of order) to the colder body.

Secondly, it is impossible for a device that operates in one cycle to produce network work from a single temperature reservoir; Network production requires heat flow from a hotter tank to a colder tank, or a single expanding tank undergoing adiabatic cooling, which performs adiabatic work. As a result, there is no possibility of a perpetual motion system.

It follows that a reduction in the increase in entropy in a specific process, such as a chemical reaction, means that it is more energy efficient.

It follows from the second law of thermodynamics that the entropy of a system that is not isolated can decrease. An air conditioner, for example, can cool the air in a room, thus reducing the entropy of the air in that system. The heat expelled from the room (the system), which the air conditioner carries and discharges to the outside air, always contributes more to the entropy of the environment than the decrease in the entropy of the air of that system. Therefore, the total entropy of the room plus the entropy of the environment increases, according to the second law of thermodynamics

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