Question

Select the pair of substances in which the one with the higher vapor pressure at a given temperature is listed first.

1. C7H16, C5H12

2. CCl4, CBr4

3. H2O, H2S

4. CH3CH2OH, CH3-O-CH3

5. Xe, Kr

Answer 1

Use the molar mass; the lower molar mass should have the higher vp.
That doesn't work for c because of H bonding in H2O. And 4 has the same molar mass the the OH on the alcohol has H bonding also. H bonding makes the boiling point higher and the vp lower.

Answer 2

4r