Question

One $\text{mole}$ of an ideal monoatomic gas is taken at a temperature of $300\text{K}$. If the volume is doubled keeping its pressure constant, change in internal energy is

• A. $450R$
• B. $600R$
• C. $500R$
• D. $400R$

Answer 1

The correct option is A $450R$

Given,
$n=1$
$f=3$ $[$ monoatomic $]$
$T_1=300\text{K}$
As volume is doubled keeping pressure constant, temperature will be doubled. Using Charle's Law,
$\therefore T_2=600\text{K}$
$\Delta T=300\text{K}$
We know, change in internal energy
$\Delta U=\frac{nfR\Delta T}{2}$
$=\frac{1\times 3\times R\times 300}{2}=450R$
Change in internal energy is $450R$ when volume is doubled.