Question

The change in entropy of 2 moles of an ideal gas upon isothermal expansion at 243.6 K from 20 litre until the pressure becomes 1 atm, is

• A. 1.385 cal/K
• B. − 1.2 cal/K
• C. 1.2 cal/K
• D. 2.77 cal/K

Answer 1

The correct option is D

2.77 cal/K

$P_1=\frac{nRT}{v_1}=\frac{2\times 0.0821\times 243.6}{20}=2atm$

$\Delta S=nRln\left(\frac{P_1}{P_2}\right)=2\times 2ln\left(2\right)\to 4\times 0.693$

$\Rightarrow 2.77cal/K$