Kinetic Theory For Matter

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Kinetic theory for matter is a theory used to explain the properties of matter. Several points of this theory that you must remember:

Matter is made up of tiny discrete particles.

• Solid: The particles are closely packed in an orderly manner.
• Liquid: The particles are loosely packed in a disorderly manner.
• Gas: The particles are randomly distributed.

The particles are in constant motion.

• Solid: Particles can only vibrate about a fixed point. (Remember that they are closely packed)
• Liquid: Particles can move about freely by sliding and rolling past each other. But there are still confined within a certain area.
• Gas: Particles are able to move about freely, usually at high speeds.

The kinetic energy of a particle changes with temperature.

• The higher the temperature, the faster the particles move.
• At fixed temperature, lighter particles move faster than heavier particles.

The average kinetic energy of all particles is directly proportional to the absolute temperature.

• At a fixed temperature, all the particles do not have the same kinetic energy. They do not travel at the same speed $\rightarrow$ there is a spread in the kinetic energy of the particles, i.e. some particles are very fast while some particles are slow.

Take note: The third and fourth point do not contradict each other. In fact, with the fourth point in place, the third point is redundant.

In summary:

Solid Liquid Gas
Particle arrangement Closely packed in orderly manner Loosely packed in disorderly manner Randomly arranged(Usually very far apart)
Particle motion Vibrate about fixed point Roll and slide past each other Move in all directions
Avg. kinetic energy Low Moderate High