Consider liquid ethane (CH3CH3) and liquid methanol (CH3OH). Which would you expect to have a larger H of vaporization?
a) It is impossible to tell unless you know the amount of each liquid involved.
b) Ethane, because it has stronger IMFs.
c) Methanol because it has a larger molar mass.
b) Methanol, because it has stronger IMFs.
d) Methanol, because it has stronger IMFs.
Answer: How large the dH of vaporization is of a substance is related to the strength of the IMFs involved, not the substance's mass nor how much of it is present. Methanol can perform hydrogen bonding (the strongest form of IMF) while ethane molecules are only held together by dispersion forces (the weakest form of IMF). Therefore, as the IMFs in methanol are greater, you would expect it to have a bigger dH of vaporization.