How do phase change occur?

Answer 1

there are three

Answer 2

Phase change in a material occurs when it changes from solid to liquid to gas; or the reverse.

The parameter changing through this series is the attraction between molecules, and their distance apart.

In a solid, the molecules are close together, and have inter-molecular bonds (shared electrons) between them.

As the temperature increases (or the pressure decreases) , the space between the molecules grows, and the sharing of inter-molecular bonds becomes more difficult. The phase state tends to the liquid.

Further heating will add sufficient energy that the vibration (movement) of the molecules overcomes any inter-molecular bonds, and the substance becomes gas.

The above ignores the triple point, which is the unique point at which the substance may exist in the three phases. And at certain areas on the phase diagram, the material may change from solid to gas without passing through the liquid phase. This is a pressure dependent phenomenon.

Solid CO2 at normal atmospheric pressure transits from solid to gas without the liquid phase. But under sufficient pressure, liquid CO2 exists, and is a very useful commercial solvent, e.g. in the removal of caffeine from coffee.

Answer 3

there are three