A sample of dry air has an initial pressure p1=1000hPa and temperature T1=300K.
ID: 803546 • Letter: A
Question
A sample of dry air has an initial pressure p1=1000hPa and temperature T1=300K. It undergoes a process that takes it to a new pressure p2=500hPa with unchanged temperature T2=T1. Compute the mechanical work per unit mass performed by the sample under the following scenarios:
(a) Isochoric pressure reduction to p2 followed by isobaric expansion to final state.
(b) Isobaric expansion to final volume 2 followed by isochoric pressure reduction to final state.
(c) isothermal expansion to final state.
Please show all steps and equations used
Explanation / Answer
a) Work done = p2 * delta v
work done per mole = R delta T
= 8.3*(300-150)
work done per kg = 8.3*(300-150)*1/0.029 = 42931J
b)Work done = p1 * delta v
work done per mole = R delta T
= 8.3*(600-300)
work done per kg = 8.3*(600-300*1/0.029 = 85862J
c) isothermal expansion
work done per kg = (8.3*300* ln 2 )/0.029
= 59515 J
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