Answer
$\Delta E_{internal}=2.49KJ$
Work Step by Step
The change in internal energy of the gas can be determined from the formula:
$\Delta E_{internal}=nC_V\Delta T$
We already know that $C_V=\frac{5}{2}R$. Therefore, the above equation can be written as:
$\Delta E_{internal}=n\frac{5}{2}R\Delta T$
Substituting the values of $n,R$ and $\Delta T$ in the formula, we get:
$\Delta E_{internal}=3\times\frac{5}{2}(8.314)(40)=2.49\times10^3J$
$\Delta E_{internal}=2.49KJ$
