Chapter 3 · Matter and Energy
3.3Classifying Matter According to Its State
8 min · two checks
Predict
Is steam a different substance from liquid water?
The idea
- Classify a sample by state.
- Explain what a change of state does and does not change.
State is about the arrangement and freedom of the particles, not about which substance you have. Ice, liquid water, and steam are one substance in three states. The names sometimes hide that: “steam” in casual speech can mean visible droplets, while chemists often mean water vapor. The classification you need here is still solid, liquid, or gas, based on shape and volume.
A solid has fixed shape and volume. A liquid has fixed volume and variable shape. A gas has neither fixed shape nor fixed volume; it expands to the container. Changing state — melting, freezing, boiling, condensing — rearranges particles without breaking them into different substances. Those are physical changes. You will compare them with chemical changes two sections from now.
Keep these
- State classifies a condition, not a chemical identity.
- Solid: fixed shape and volume. Liquid: fixed volume. Gas: fills the container.
- Changes of state are physical changes.