Home » Handbook of O Level Physics » UNIT 9: SIMPLE KINETIC THEORY OF MATTER


  • Properties of states of matter:

    • Solids have a fixed volume and shape.

    • Liquids have a fixed volume but no fixed shape.

    • Gases have no fixed volume. They spread out to fill all the space available to them. Gases have least density. Unlike solids and liquids, gases can be compressed.

  • Kinetic theory of matter: According to this theory, molecules of solids, liquids and gases are in continuous random motion.

    • In solids, molecules vibrate about fixed positions and they have minimum space between them. There are strong intermolecular forces between molecules.

    • In liquids, molecules are not fixed in their positions. Molecules have slightly more space between them compared to solids. Intremolecular forces are weaker than in solids but still fairly strong.

    • In gases, molecules have high kinetic energy and the intermolecular forces are negligible. Average distance between molecules is greatest.

  • Evidence of molecular motion

    • Diffusion

    • Reflections from smoke particles in a glass cell are observed using a microscope. The smoke particles show random motion because of the air molecules bombarding them.

    • Observing pollen on the surface of water

  • Kinetic theory of matter can be used to explain a range of phenomena including:

    • diffusion

    • evaporation

    • pressure of a gas

    • fixed shape of a solid

    • expansion

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