Chapter 10, Problem 99RQ

Uranium hexafluoride is a white solid that readily passes directly into the vapor state. (Its vapor pressure at $\text{20}\text{.0 °C}$ is 120 torr.) A trace of the uranium in this compound—about 0.7%—is uranium-235, which can be used in a nuclear power plant. The rest of the uranium is essentially uranium-238, and its presence interferes with these applications for uranium-235. Gas effusion of ${\text{UF}}_{\text{6}}$ can be used to separate the fluoride made from uranium-235 and the fluoride made from uranium-238. Which hexafluoride effuses more rapidly? By how much? (You can check your answer by reading Chemistry and Current Affairs 10.1 in Section 10.6.)