Question

The maximum work which a system can perform at constant
temperature and pressure equals
(a) ∆H – ∆E (b) (– ∆G)
(c) q – ∆E (d) P.∆V – ∆G

Answer 1

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Answer 2

The maximum work which a system can perform at constant temperature and pressure equals (b) (– ∆G) as:

1. ΔH is the heat absorbed by the system (since the process is at constant temperature and pressure), so equivalently −ΔH energy is obtained from the system after doing expansion work.

2. Since ΔS is the entropy created in the process, at the very least −ΔS entropy must be created in the surroundings - that is, at least −TΔS energy must be lost as heat. This comes from the −ΔH, and thus leaves −ΔH+TΔS to do useful work. No more work can be done than this. 3. 3. −ΔH+TΔS is −ΔG, so −ΔG is the maximum possible useful work.