What is the Kinetic Molecular Theory of Matter?

The Kinetic Molecular Theory of Matter is a concept that basically states that atoms and molecules possess an energy of motion (kinetic energy) that we perceive as temperature. In other words, atoms and molecules are constantly in motion , and we measure the energy of these movements as the temperature of that substance. This means if there is an increase in temperature, the atoms and molecules will gain more energy (kinetic energy) and move even faster.



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This kinetic-molecular theory states (postulates) that:

  • All matter (solid, liquid, and gas) is made up of tiny particles called atoms, or atoms that are joined to form molecules.
  • These particles are in constant motion.
  • Molecular motion is random.
  • Particles in motion possess kinetic energy.
  • Their motion increase as they gain energy.
  • There is an exchange (transfer) of energy between particles (atoms and molecules) during a collision between them.
  • Particles (molecules) in gases do not exert large forces on each other, unless they are in collision with each other.
  • Collisions between these particles are perfectly elastic.
  • Molecular motion is greatest in gases, less in liquids, and least in solids.
  • Solids retain a fixed volume and shape – particles are tightly packed, usually in a regular pattern.
  • Liquids assume the shape of the container which it occupies but maintain their volume – particles close together with no regular arrangement.
  • Gases assumes the shape and volume of its container and will expand to fill a container of any size – particles are very well far apart with no regular arrangement.

The kinetic molecular theory is very useful in explaining or describing the forces between molecules and the energy that they possess, as well as, the effects of thermal energy, temperature and pressure on matter.