How would you explain the difference between a solid a liquid and a gas to a student who isn't taking science class?

Answer 1

The difference between the states (phases) of matter is a property of the energy within their molecules. This energy determines how the molecules will interact with each other in the same element or compound. By adding energy, or removing energy, you can change a substance's phase.

If the molecules are tightly packed with low energy, the substance is solid. With greater energy, the molecules stick together but move around each other, and the substance is a liquid. With even greater energy, the molecules push each other apart and become disorganized, and lose much of their coherence and their fixed volume, existing as a gas.

The particular form of a substance's atoms or molecules determines the temperature at which phase changes occur. So some substances are naturally solids, liquids, or gases at normal temperatures. If elements react with other elements to form compounds, the molecules may adopt a phase with less energy, or one with more energy.

e.g. solid sodium and gaseous chlorine = solid table salt

e.g. gaseous hydrogen and gaseous oxygen = liquid water

e.g. solid carbon and gaseous oxygen = gaseous carbon dioxide