Question

Which solution has the higher vapor pressure? `(A)` A solution that boils at `100^@ "C"` `(B)` A solution that boils at `-33^@ "C"`

`(A)` A solution that boils at `100^@ "C"`
`(B)` A solution that boils at `-33^@ "C"`

Answer 1

Vapor pressure is just the amount of gas in the liquid-gas equilibrium; the higher the vapor pressure, the more gas there is, and thus the vaporization can occur more easily, as it is easier to shift the liquid-gas equilibrium to vaporize more liquid into gas when there is a lot of gas.

`A` has the higher boiling point, so it is harder to vaporize, since you have to reach a higher temperature for the vapor pressure to equal the atmospheric pressure, which would be what makes the vaporization occur.

Since `A` is harder to vaporize, it has the lower vapor pressure. Therefore, `B` has the higher vapor pressure.

If that isn't enough detail, I've covered it in more detail here.