Matter
ICSE Class 8 · Physics · Chapter 1
What this chapter covers
- The kinetic theory of matter
- The three states of matter and the movement of particles
- Energy content of the three states
- Melting and freezing
- Boiling, evaporation and vaporisation
- Condensation
- Sublimation and deposition
- Change-of-state diagrams
Key definitions
Matter is anything that has mass and takes up space.
The kinetic theory of matter is the idea that all matter is made of tiny particles that are always moving.
Kinetic energy is the energy that a body has because it is moving.
A solid is a state of matter that has a fixed shape and a fixed volume.
A liquid is a state of matter that has a fixed volume but no fixed shape.
A gas is a state of matter that has neither a fixed shape nor a fixed volume.
Temperature is a measure of how hot or cold a body is.
A change of state is the change of a substance from one of the three states to another, caused by heating or cooling.
Melting is the change of a solid into a liquid when it is heated.
The melting point is the fixed temperature at which a pure solid changes into a liquid.
Freezing is the change of a liquid into a solid when it is cooled.
Vaporisation is the change of a liquid into a gas.
Key points
- Matter is anything that has mass and takes up space.
- The kinetic theory of matter says that all matter is made of tiny particles that are always moving.
- Heating gives the particles more energy and makes them move faster; cooling does the opposite.
- In a solid, particles are close, have the least energy and only vibrate; a solid has a fixed shape and volume.
- In a liquid, particles are close but have more energy and slide past one another; a liquid has a fixed volume but no fixed shape.
- In a gas, particles are far apart, have the most energy and move freely at high speed; a gas has no fixed shape or volume.
- For the same substance, the gas holds the most energy and the solid the least.
- Melting (fusion) turns a solid into a liquid; freezing turns a liquid into a solid.
- Vaporisation turns a liquid into a gas, either by boiling throughout the liquid at a fixed temperature or by evaporation from the surface at any temperature below the boiling point.
- Condensation turns a gas into a liquid on cooling.
- Sublimation turns a solid directly into a gas; deposition turns a gas directly into a solid.
- A pure substance melts and boils at fixed temperatures; pure water melts at 0 °C and boils at 100 °C at sea level.
- In a change-of-state diagram, changes towards the gas need heat added and changes away from the gas give heat out.