# How to determine which gas is more soluble

I have a chemistry homework problem that asks whether $Br_2$ or $O_2$ is more soluble in water in room temperature. However, I can't seem to find a way to figure it out, short of looking it up.

Is there a guiding rule for such figures, such as relating to molar mass?

• The answer the question is seeking might be simpler than you think. The most obvious difference between oxygen and bromine is that bromine is a liquid not a gas a room temperature. Might this be significant? – matt_black Jan 18 '14 at 13:52

$\ce{O_2}$ and $\ce{Br_2}$ have no permanent dipole so the only interactions are Debye forces (interaction between water permanent dipole and a gas molecule induced dipole) and London forces (between instantaneous dipoles).
This is the reason why van der waals forces are stronger for bigger atoms. This would explain why $\ce{Br_2}$ has a better solubility than $\ce{O_2}$ in water.
London interactions are very important if you look at liquefaction temperature of gases. For instance, it explains why $\ce{Ar}$ becomes a liquid below 87K while $\ce{He}$ become a liquid only below 4K.