The second law of thermodynamics states that the total amount of disorder—
the totalentropy—of a system plus its surroundings will never decrease.
A heat engine is a device that uses heat to produce useful work. To determine
the efficiency of a heat engine, use the formula
. Unless QC = 0, the engine’s efficiency is always less than 1.
For a Carnot engine,
The change of internal energy is zero for a closed path on a P−V diagram.