Predict What has the weakest intermolecular attractions based only on vapor pressure data.

(a) butyl alcohol (vapor pressure at 293 K = 6 torr)

(b) ethyl ether (vapor pressure at 293 K = 450 torr)

(c) pentane (vapor pressure at 293 K = 430 torr)

(d) propionic acid (vapor pressure at 293 K = 5 torr)

Answer: Based only on vapor pressure data, ethyl ether (vapor pressure at 293 K = 450 torr) has the weakest intermolecular attractions. The correct option is B.

Explanation:

Vapour pressure can be defined as the pressure created by vapour of a substance (gas or liquid) in thermodynamic equilibrium state in a closed container at a certain temperature.

Factor which affects the vapour pressure of a substance includes:

- surface area

- intermolecular forces and

- temperature.

Strong intermolecular attractions between molecules in a medium produce a lower rate of evaporation and a lower vapour pressure. While weak intermolecular attraction between molecules in a medium produce a higher rate of evaporation and a higher vapour pressure.

From the options listed above, ethyl ether has the highest vapour pressure at the same temperature with others, therefore it will have the weakest intermolecular attractions.