ThermodynamicsHard

Question

A quantity of 1.6 g helium gas is expanded adiabatically 3.0 times and then compressed isobarically to the initial volume. Assume ideal behaviour of gas and both the processes to be reversible. The entropy change of the gas in this process is (ln 3 = 1.1)

Options

A.−1.1 cal/K
B.+1.1 cal/K
C.−2.2 cal/K
D.+2.2 cal/K

Solution

$\Delta S = \Delta S_{\text{adiabatic}} + \Delta S_{isobaric} = 0 + n.C_{P,m}.\ln\frac{T_{2}}{T_{1}}$

$= \frac{1.6}{4} \times \frac{5R}{2} \times \ln\frac{1}{3} = - 2.2\text{ Cal/K}$

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