How would you justify that ice, water and water vapour are three stages of matters of a substance and not different substances?

Experimentally, you could fill an afternoon with these fun activities:

- - Take ice. Warm it and you get water. Warm it more and you get water vapor.

- - Take water. Cool it and you get ice. Warm it and you get water vapor.

- - Take water vapor. Cool it and you get water. Cool it more and you get ice.

- - Each time you get a liquid, you could pull a few moves with it with various

chemicals, flavors, additives, weigh it, measure it, etc. and prove that the liquids

are all the same substance.

These experimental results show that ice, water, and water vapor are three

different manifestations of the same substance.

The molecule is still H2O, it just isn't bonded with other H2O molecules when it's a gas.