Question

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

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

Answer 1

Answer: (D)

$2.77cal/K$

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

Given:

$P_1=1atm$

No. of moles = 2 mol

T = 243.6 K

V = 20 litre

We know,

$PV=nRT$

$P=\frac{nRT}{V}$

$P=\frac{2\times 0.0821\times 243.6}{20}$

$P=2atm$

$\Delta S=-4Rln\frac{P_2}{P_1}$

$\Delta S=-4\times \frac{8.314}{4.19}ln\frac{2}{1}$

$\Delta S=2\times 0.6931\times 1.9=2.77cal/K$

Change in entropy is $2.77cal/K$