Answer
$-1.93 \times 10^{3} \mathrm{J}$
Work Step by Step
The change in the internal energy is
$$\Delta E_{\text {int }}=n C_{V} \Delta T=\frac{3}{2} n R \Delta T=\frac{3}{2}(1.00 \mathrm{mol})(8.31 \mathrm{J} / \mathrm{mol} \cdot \mathrm{K})(300 \mathrm{K}-455 \mathrm{K})$$$$=-1.93 \times 10^{3} \mathrm{J}$$
