Question

When the following subtances go from liquid to solid, which would require the lowest temp for it to freeze: Ar, C6H12, HF, NaCI, Cu Why?

Answer 1

Molecules with stronger intermolecular force have higher freezing points.

Let’s look at it from the point of view of a solid, where the particles are held in position by their intermolecular forces of attraction. If we raise the temperature enough to overcome these forces, the solid will melt. A solid with high intermolecular forces will require more energy (i.e., a higher temperature) to overcome these attractions and will have a higher melting point.

Conversely, as the temperature of a liquid sample decreases, the average kinetic energy of the molecules decreases and they move more slowly. Since the molecules are near each other, the slower they go, the more the intermolecular forces attract them to each other. Molecules with stronger intermolecular forces are pulled together tightly to form a solid at higher temperatures, so their freezing point is higher. Molecules with lower intermolecular forces will not solidify until the temperature is lowered further.

Freezing point of the following substances

NaCl- 801 ⁰C

Cu - 1085⁰ C

Ar - 5.5

C6H12 - 6.6

HF - -83.6

SO out of these HF require the lowest temperture to freeze

Sources - http://socratic.org/questions/how-do-intermolecular-forces-affect-freezing-point-1