Question

How do the physical properties of molecules with strong intermolecular forces compare with those of molecules with weak attractive forces?

Answer 1

Molecules with stronger intermolecular force have higher melting points, boiling points, and viscosity. They have lower vapour pressures and evaporation rates.

MELTING POINT

The intermolecular attractions hold the particles of a solid in position. A solid with high intermolecular forces requires more energy to overcome these attractions. It has a higher melting point.

BOILING POINT

The molecules in a liquid are able to slide past each other. A high temperature gives the molecules enough kinetic energy to break away and escape into the gas phase. Liquids with strong intermolecular forces have higher boiling points.

VISCOSITY

The resistance of a liquid to flow depends on the ease with which molecules can move past each other. Viscosity increases with stronger intermolecular forces.

VAPOUR PRESSURE AND EVAPORATION RATE

If the intermolecular forces in a liquid are small, the molecules need little energy to separate from each other. More molecules escape into the atmosphere. The vapour pressure and the rate of evaporation are high.

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