Phase change facts for kids

A phase change is when something changes its form, like when ice melts into water. It's a way that matter can switch between being a solid, a liquid, or a gas. These changes often happen because the temperature or pressure changes.

What Happens During a Phase Change?

When matter changes its state, we call it a phase change. Think about water: it can be ice (a solid), liquid water (a liquid), or steam (a gas). Each of these is a different state of matter.

Different Kinds of Phase Changes

Matter can change from one state to another in several ways.

• Melting: When a solid turns into a liquid. An example is an ice cube melting into water.
• Evaporation: When a liquid turns into a gas. This happens when water boils and turns into steam.
• Sublimation: When a solid turns directly into a gas, without becoming a liquid first. Dry ice (solid carbon dioxide) does this.
• Condensation: When a gas turns into a liquid. This is how clouds form, or how water droplets appear on a cold glass.
• Solidification: When a liquid turns into a solid. This is also called freezing, like when water turns into ice.
• Deposition: When a gas turns directly into a solid, without becoming a liquid first. Frost forming on a cold window is an example.

How Particles Behave in Different States

The way tiny particles are arranged and move changes in each state of matter.

• Solids: In a solid, particles are packed very closely together. They are held by strong forces, like tiny magnets. This gives solids a definite shape and volume. They can only vibrate in place.
• Liquids: When a solid gets enough heat, it melts into a liquid. In a liquid, the particles are still close, but the forces holding them are weaker. This lets them slide past each other. A liquid has a definite volume but takes the shape of its container.
• Gases: If a liquid gets even more heat, it evaporates into a gas. In a gas, the particles are far apart and move very fast. There are almost no forces holding them together. A gas has no definite shape or volume and will spread out to fill any container.

Adding or Releasing Heat

Phase changes are all about energy, usually heat energy.

• Adding Heat: To go from a solid to a liquid, or a liquid to a gas, you need to add heat. For example, you add heat to ice to make it melt. You add more heat to water to make it boil and turn into steam.
• Releasing Heat: To go from a gas to a liquid, or a liquid to a solid, heat energy is released. When steam turns back into water, it releases heat. When water freezes into ice, it also releases heat.

An Everyday Example: The Ice Cube

Think about an ice cube to understand phase changes easily. 1. An ice cube is a solid. 2. If you leave it out, it gets warmer and melts into liquid water. 3. If you heat that water on a stove, it will evaporate and turn into water vapor, which is a gas. 4. If that water vapor cools down, it will condense back into liquid water. 5. If you put that liquid water in a freezer, it will solidify (freeze) back into a solid ice cube.