Physics GRE Discussion Forums

The gas used in separating the two uranium isotopes 23'U
and 238U has the formula UF6. Ifyou added heat at equal rates to a
mole of UF6 gas and a mole of H2 gas, which one's temperature
would you expect to rise faster? Explain.

I realize that this is an older post, but I will respond in the hopes my solution may be helpful to other readers.

I'm not entirely sure, but I believe that the important factor may be the size difference of $$UF_6$$ and $$H_2$$. If we look at the Equation of State for Gas with nonzero size and a pairwise attractive force $$$\left( P + \dfrac{N^2 a}{V^2} \right) \left(V - N b\right) = N k_B T$$$ where a is the force between particles and b is the size of the particles. We then note that for $$UF_6$$ the size is bigger and thus the volume portion should become smaller than for $$H_2$$. I would therefore assume that the temperature of $$H_2$$ should rise faster.

I hope this makes sense. If anyone has any questions, or sees a flaw in this argument, please feel free to reply.

Thanks.