Physics question -please help!?

Question

It is expected that the melting point would increase if the experiment isconducted at a lower altitude. Explain briefly why this happens with refernece to the packing of the molecules.

Answer 1

For most substances, but not water, the molecules are closer together in the solid than than the liquid (random orientation) because of the ordered way they are packed in the solid. This means they will occupy a greater volume in the liquid form. Since the atmospheric pressure exerts a force that resist expansion, the higher the pressure the more energy (higher temperature) it takes to expand to its liquid form.