Question

How do intermolecular forces affect vapor pressure?

Answer 1

By facilitating or hindering the random movement of molecules.

Vapor Pressure is the pressure a gas exerts on its liquid or solid state. The higher it is the more likely the molecules of its liquid or solid will overcome the atmospheric pressure, break loose, and turn into gas.

Many factors effect the "breaking loose" phenomenon, one of them is the intermolecular forces. The stronger these forces, the more tightly packed molecules are, and the harder for them to break loose.

I hope that answered your question.

Sources & Further Reading:
Vapor Pressure
Intermolecular Forces