Question

List all the intermolecular forces for each molecule. Predict the order of increasing vapor pressure at a given temperature for the following compounds.

FCH₂CH₂F

HOCH₂CH₂OH

FCH₂CH₂OH

Answer 1

FCH2CH2F - Induced Dipole force

HOCH2CH2OH - Induced Dipole Force , Hydrogen bonding

FCH2CH2OH - Induced Dipole Force , Hydrogen bonding(only at one end)

The order of increasing vapor pressure is HOCH2CH2OH < FCH2CH2OH < FCH2CH2F , because there is no hydrogen bonding in the third molecule and the second molecule can hydrogen-bond at only one end and the first molecule can hydrogen-bond at both ends for the strongest interaction. Now as the strength of interaction increases the vapour pressure decreases. So, FCH2CH2F which has the least interaction will have highest vapour pressure followed by FCH2CH2OH because it can hydrogen bond at one end only and HOCH2CH2OH has lowest vapour pressure because it has highest interaction due to hydrogen bonding at both ends.