L3 slide 5: Entropy change and exergy (ENGR5003)

L3 slide 5: Entropy change and exergyFrom lectureCurrent specThird2 marks3 min

Two quick questions on entropy and exergy.

Formulas you may need

Entropy definition: $dS = \left(\dfrac{\delta Q}{T}\right)_{rev}$ (on the formula sheet)
Exergy of heat $q$ at temperature $T$ : $e_{x,Q} = q\left(1 - \dfrac{T_0}{T}\right)$ (on the formula sheet)

(a)
A system undergoes a reversible process during which it receives 200 J of heat at a constant temperature of 400 K. What is the entropy change of the system?
A2 J/KB0.50 J/KC-0.50 J/KD0 J/K
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(b)
Which statement best describes exergy?
AThe total energy contained in a systemBThe maximum useful work that can be obtained as a system reaches equilibrium with its surroundingsCThe heat transferred from a high-temperature reservoirDThe energy that must always be conserved during a process
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