Physical changes

This lesson covers: 

  1. Characteristics of physical changes
  2. Changes of state as examples of physical changes
  3. How heating and cooling affects particles during changes of state

Physical changes

Diagram showing the physical change from ice to water.

Physical changes rearrange particles or alter their energy levels but do not form new substances.

This means the total mass stays constant when changing between states of matter.

Examples include changes of state (solid, liquid, gas), dissolving, and breaking objects.

Changes of state are physical changes

Diagram showing transitions of matter between solid, liquid, and gas states including sublimation, melting, freezing, boiling, and condensing.

Changes of state describe the transition of matter from one state (solid, liquid or gas) into another state.

These transitions occur without altering the chemical composition of the substance.

Some substances can transition directly between the solid and gas states without entering the liquid phase. This is called sublimation.

Dissolving substances

Diagram showing 30g of salt mixed with 100g of water to form a 130g salt solution.
  1. When a solid dissolves, its particles mix with a liquid solvent.
  2. The total mass remains constant as no new substances are made.
  3. Dissolving can be reversed by evaporating the solvent.

How changes of state alter properties

Diagram showing particle arrangement in solid, liquid, and gas states.
  1. Solids have tightly-packed particles, making them incompressible and unable to flow.
  2. Liquids and gases have free-moving particles, allowing them to flow and change shape.
  3. Gases have large spaces between the particles making them easy to compress.

Ice is an unusual solid

Diagram showing that ice is less dense than water, allowing it to float.

In most substances, density decreases during state change from a solid to a liquid and from a liquid to a gas.,

However, water is an anomaly—ice is less dense than liquid water, allowing it to float.