entropy and therefore 2) energy transfer always decreases (or preserves) total free energy and increases (or preserves) total energy stored as heat. As a result, any time energy is transformed or transferred, the amount of free energy available with which to do work either stays the same or decreases. The conversion efficiency of energy transfer refers to the ratio of total work done divided by total heat transferred, and per the above laws of thermodynamics it is always less than 100%.

Heat engines