L1 slide 21: First law, compression with heat rejection (ENGR5003)

L1 slide 21: First law, compression with heat rejectionFrom lectureCurrent specThird3 marks3 min

A gas is compressed in a piston-cylinder. During the process, 50 kJ of work is done on the gas, while 20 kJ of heat is rejected from the gas.

Formulas you may need

First law, closed system: $Q = \Delta U + W$ , with $W > 0$ when work is done BY the system (on the formula sheet)
Reversible boundary work: $\delta w = p\,dv$ (on the formula sheet)
Reversible heat: $\delta q = T\,ds$ (on the formula sheet)

(a)
What is the change in internal energy of the gas?
A-70 kJB-30 kJC+30 kJD+70 kJ
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(b)
What is the expansion/compression work in a reversible process?
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(c)
How do you calculate the heat in a reversible process?
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