Any change from a solid to a liquid is called melting. In most pure substances this occurs at a specific temperature, called the melting point. Thermal energy makes the molecules in a substance vibrate faster, raising their temperature. At its melting point, the particles of a solid substance are vibrating so fast that they break free of their fixed positions. Water’s melting point is 0 ˚ C.

The change of state from liquid to solid is called freezing (it is just the reverse of melting). At its freezing temperature, the particles of a liquid are moving so slowly that they begin to form regular patterns. When you put water in a freezer, it slowly loses energy in the cold air. The molecules move more and more slowly until they become locked into place. Water freezes at 0 ˚ C. Even wax turning back into a solid is considered “freezing.”

Freezing Hot Water vs Cold Water Shooting a super-soaker at -45F

Changing from a liquid to a gas is called vaporization. It takes place when particles in a liquid gain enough energy to form a gas. The particles speed up from the thermal energy and break their loose bonds with each other. There are two types of vaporization: Evaporation Boiling

Evaporation is when vaporization only takes place on the surface of the liquid. A shrinking puddle is an example, water in the puddle gains energy from the ground, the air, or the sun, and the surface molecules can turn to gas.

Boiling occurs when a liquid changes to a gas below its surface as well as at the surface. You can see this because the liquid bubbles. The temperature at which a substance will boil is called its boiling point. The boiling point of water is 100 ˚ C, unless the air pressure is lower, then the boiling point drops.

The opposite of vaporization is condensation. Condensation occurs when particles in a gas lose enough thermal energy to form a liquid. The molecules slow down as they cool, and form loose bonds with each other, creating a liquid. You cannot see water vapor. It is a colorless gas that is impossible to see. The steam you see above a boiling pot is not water vapor, neither are clouds. They are tiny droplets of liquid water.

Sublimation Accelerated Sublimation