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
. If we look at the Equation of State for Gas with nonzero size and a pairwise attractive force
where a is the force between particles and b is the size of the particles. We then note that for
the size is bigger and thus the volume portion should become smaller than for
. I would therefore assume that the temperature of
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.