Uranium- 235 is used as a fuel in nuclear power plants. Since natural uranium contains only a small amount of this isotope, the uranium must be enriched in uranium-235 before it can be used. To do this, uranium(IV) oxide is first converted to a gaseous compound, $\mathrm{UF}_{6}$, and the isotopes are separated by a gaseous diffusion technique. Some key reactions are
$$
\begin{gathered}
\mathrm{UO}_{2}(\mathrm{~s})+4 \mathrm{HF}(\mathrm{g}) \longrightarrow \mathrm{UF}_{4}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \\
\mathrm{UF}_{4}(\mathrm{~s})+\mathrm{F}_{2}(\mathrm{~g}) \longrightarrow \mathrm{UF}_{6}(\mathrm{~g})
\end{gathered}
$$
How much thermal energy transfer (at constant pressure) would be involved in producing 225 ton $\mathrm{UF}_{6}(\mathrm{~g})$ from $\mathrm{UO}_{2}(\mathrm{~s})\left(1 \mathrm{ton}=9.08 \times 10^{5} \mathrm{~g}\right) ?$ Some necessary standard
enthalpies of formation are
$$
\begin{aligned}
\Delta H_{f}^{\circ}\left\{\mathrm{UO}_{2}(\mathrm{~s})\right\} &=-1085 \mathrm{~kJ} / \mathrm{mol} \\
\Delta H_{f}^{\circ}\left\{\mathrm{UF}_{4}(\mathrm{~s})\right\} &=-1914 \mathrm{~kJ} / \mathrm{mol} \\
\Delta H_{f}^{\circ}\left\{\mathrm{UF}_{6}(\mathrm{~g})\right\} &=-2147 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}
$$