# Chapter 16 - Think and Explain: 59

The faster uranium hexafluoride molecules containing U-235 will diffuse at a greater rate than the slower molecules containing U-238.

#### Work Step by Step

Assume they are at the same temperature. This means they have the same average translational kinetic energy per molecule. $KE = \frac{1}{2} mv^{2}$. The mass of a $UF_{6}$ molecule containing U-235 is less than that of a uranium hexafluoride molecule containing U-238, so the speed v must be greater to have the same average kinetic energy.

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