Question

What limits the amount of work that a system can do?
short paragraph

Answer 1

The amount of work a system can do is limited by the energy available and by thermodynamic laws: the first law (energy conservation) means work cannot exceed the energy extracted from the system, and the second law (entropy increase) prevents all of that energy from being converted into work. For heat engines the Carnot efficiency, η = 1 − Tc/Th, gives the maximal fraction of heat convertible to work; more generally the maximum useful work equals the decrease in free energy (Helmholtz or Gibbs, depending on conditions). Irreversibilities—friction, heat losses and finite temperature differences—further reduce the achievable work.