Solid, Liquid and GasSolid, Liquid and Gas

According to the simple kinetic model, solids, liquids and gases are made up of tiny moving or vibrating particles.

are held tightly and packed fairly close together – they are strongly attracted to each other

  • o are in fixed positions but they do vibrate
are fairly close together with some attraction between them

  • are able to move around in all directions but movement is limited by attractions between particles
have little attraction between them

  • are free to move in all directions and collide with each other and with the walls of a container and are widely spaced out

Brownian motion is the random, erratic, continuous motion of tiny particles suspended in water or air. The kinetic model of matter explains this: randomly moving air or water particles hit the smoke or pollen particles unevenly, causing zigzag motion. We see that air molecules must be much smaller in mass than pollen particles and that they hit them on all sides.

  1. Air molecules move randomly, in different directions
  2. They have a range of speeds and move continuously
  3. Air molecules have a much smaller mass than smoke particles
  4. They hit the smoke particle from all sides

Internal energy is sum of the random distribution of kinetic and potential energies associated with the molecules of a system. At 0K all particles have the minimum possible internal energy, but above this energy is proportional to temperature.

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  1. Kinetic energy depends on mass and speed. It is proportional to temperature.
  2. Potential energy is caused by interactions between particles and is based on their positions relative to one another.

When a substance changes phase, its internal energy changes but its kinetic energy doesn’t. This is because the change of phase alters the bonds and therefore the potential energy if the particles. Work is done in moving the molecules apart. This means that temperature stops changing during a phase change. When heating a substance without a phase change, KE and PE increase.