Ice, water and steam

Ice, water and steam are the same stuff in three states. Heat it and the tiny particles move faster: ice melts into water, and water boils into steam. Cool it and it goes back the other way.

While ice is melting, its temperature stays at 0 °C until it has all turned to water; the heat goes into loosening the particles, not warming them. Water boils at 100 °C at sea level, and at a lower temperature high on a mountain, where the air presses down less.