Introduction

When you see water boiling, what do you think is happening?

Before the water can boil, heat energy must be applied.

Once the water absorbs a certain amount of energy, a phase change occurs.

In chemistry, a phase change is when matter transitions from one state of matter to another.

All phase changes require a change in energy.

For example, this ice cube is made of solid water.

When ice is left out at room temperature, its energy increases, and it begins to change from a solid to a liquid.

Do you know what a phase change from solid to liquid is called?

If you said “melting,” you are right!

Phase changes, like melting, are physical changes, and they are reversible.

This means that each phase change has an opposite phase change.

Which phase change is the opposite of melting?

When the energy of liquid water goes down, it will transition into a solid.

This phase change is called freezing.

Melting and freezing are opposite phase changes between a liquid and a solid.

Which two states of matter are involved when boiling water?

Boiling water is a type of phase change between a liquid and a gas called vaporization.

The opposite phase change to vaporization is called condensation.

The water droplets on a cold water bottle are a product of condensation, and they are made of molecules from the water vapor in the air.

Phase changes are happening around you every day. They create the clouds, they create the rain,

and occasionally they try to ruin a good ice cream cone!