Final answer:
The work done by a heat engine is the difference between the heat absorbed from the hot reservoir and the heat released into the cold reservoir (W = Qh - Qc), which represents the net heat converted into work.
Step-by-step explanation:
The work done by a heat engine is best described as the difference between the heat coming in and the heat flowing out. To elaborate, the heat engine takes in heat energy (Qh) from a high-temperature source (hot reservoir) and disposes of some unused energy (Qc) into a low-temperature sink (cold reservoir). The work (W) performed by the engine is the net heat transfer into the system, which can be calculated as W = Qh - Qc. This is because the heat engine operates on a cyclical process, and the efficiency of the heat engine is determined by the ratio of this work output to the amount of energy input.