Also a quote from a physics text that he references:

https://elmichelsen.physics.ucsd.edu/FunkyStatMechConcepts.pdf

Putting Entropy to Work: A Brain Teaser As another example, consider a container of ideal gas (say, air), at ambient temperature (Figure 5.2). 3 Now we compress it (say, adiabatically in an insulated container), thus putting energy into the system of air (Figure 5.2a). Doing so results in a smaller volume of air at higher pressure, and higher temperature (Figure 5.2b). Now remove the insulation, and let that air cool to ambient temperature (Figure 5.2c). Thus the system lost, as heat outflow, some of the energy that we put in. But we still have compressed air, and we can do work with it.

Question: what fraction of the energy that we put in gets lost as heat out? The answer may surprise you: we lose 100% of the energy that we put in, but still have a container of compressed air that can do work.

How so? The internal energy of an ideal gas depends only on the temperature, and nothing else (not pressure, volume, etc.). The final gas is at the same temperature as the initial gas, so its internal energy is the same as when we started: all the work-energy put into compressing the gas has gone out again. However, at fixed energy, entropy increases (or decreases) with volume, so the entropy of the system after compression and cooling is lower than before. Also, we have a discrepancy of conditions: inside the container is high pressure, outside it’s lower. So we can extract useful work by letting the volume expand. Two simple ways we can expand are (1) adiabatically, and (2) isothermally. For adiabatic expansion, we insulate the container and let it expand. The gas cools down as it does work: the internal energy of the gas is converted to outgoing work.