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Matter and Its Composition: Law of Conservation of Mass

Kinetic theory of matter

The kinetic theory of matter is a theory that tells us about the behaviour of matter.

Kinetic Theory of Gases

  • All matter is made up of molecules.

  • All molecules of a substance are identical.

  • Molecules of different substances differ in composition, shape and size.

  • Molecules are in continuous motion; they don’t stop for any length of time.

  • Intermolecular forces depend on the distance between the molecules and the type of molecules.

  • Motion of molecules is affected by the change in temperature; the higher the temperature, the more they move.

Intermolecular force is an attractive force between molecules. It depends on the distance between molecules.

  • Arrangement of molecules in Solids

  • In solids, molecules are very tightly packed because of very strong intermolecular forces between them.

  • The molecules can only vibrate, but cannot move from their respective positions. This is because strong intermolecular force holds the molecules at one place. For the same reason, solids are rigid and hard.

So, solids have a fixed shape and a fixed volume, and thus, cannot be compressed.

When we heat solids, they gain heat energy. This energy increases the vibrations of the molecules. Due to the increase in vibrations, the intermolecular spaces increase, which in turn leads to the expansion of solids. Thus, solids expand on heating.

  • Arrangement of molecules in Liquids

  • Molecules are slightly further apart than in solids.

  • Intermolecular forces are less strong than in solids.

  • Molecules can move from their positions in liquids.

  • Thus, liquids flow, and take the shape of containers.

  • Liquids do not have a definite shape, but they do have a definite volume.

  • When we heat a liquid, its molecules vibrate. As the intermolecular forces are weaker in liquids than in solids, the molecules of the liquid also move vigorously. Thus, liquids also expand on heating, but only slightly

  • As there i…

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