Question

Find the change in internal energy of $3\text{mol}$ of helium gas when its temperature is increased by $2\text{K}$.

• A. $7.48\text{J}$
• B. $12\text{J}$
• C. $74.8\text{J}$
• D. $74.8\text{cal}$

Answer 1

The correct option is C $74.8\text{J}$

Helium is a monoatomic gas.
Internal energy of $n$ moles of gas is $U=\frac{3}{2}nRT$
$\Rightarrow \Delta U=\frac{3}{2}nR\Delta T$
$=\frac{3}{2}\times 3\times 8.31\times 2=74.8\text{J}$