$\begin{aligned}
& \Delta \mathrm{U}=\mathrm{q}+\mathrm{w}(\mathrm{q}=0) \
& \mathrm{nC}{\mathrm{V}} \Delta \mathrm{T}=-\mathrm{P}{\mathrm{ext}}\left(\mathrm{V}_2-\mathrm{V}_1\right) \
& \mathrm{V}_2=2 \mathrm{V}_1 \
& \frac{\mathrm{nRT}_2}{\mathrm{P}_2}=\frac{2 \mathrm{nRT}_1}{\mathrm{P}_1} \
& \mathrm{P}_1=5, \mathrm{T}_1=298 \
& \mathrm{P}_2=\frac{5 \mathrm{~T}_2}{2 \times 298} \
& \mathrm{n} \frac{5}{2} \mathrm{R}\left(\mathrm{T}_2-\mathrm{T}_1\right)=-1\left(\frac{\mathrm{nRT}_2}{\mathrm{P}_1}-\frac{\mathrm{nRT}_1}{\mathrm{P}_1}\right)
\end{aligned}$
Put T1=298 and P2=2×2985 T2 Solve and we get T2=274.16 K T2≈274 K