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| Kinetic Theory of Matter |
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| This theory explains the physical properties of matter in terms of motion of its molecules. According to this theory, every substance (solid, liquid or gas) consists of a large number of minute particles called molecules. A molecule may be defined as the smallest particle of a substance that can exist in free state and has all the characteristics of the present substance. |
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| The molecules are in continuous random motion. They possess all possible velocities in all possible directions. When a body is cooled, there is a decrease in the molecular motion. When a body is heated, there is an increase in molecular motion. |
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| The energy possessed by molecules is of two forms - kinetic energy and potential energy. The kinetic energy manifests itself in molecular motion. The potential energy manifests either in the expansion of a substance or in change of its state. The heat supplied to a body partly increases the kinetic energy and partly increases the potential energy of the molecules. |
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| To sum it up, the kinetic theory of matter is based upon the following points: |
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 Matter consists of molecules. These are the smallest particles, which are capable of free existence and retain all the chemical properties of the parent substance. |
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 The molecules are always in a state of random continuous motion. |
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 The molecules exert forces on one another. These forces depend upon intermolecular distance. |
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| The intermolecular distances are greater in gases than in solids or liquids. As a result, the intermolecular forces of attraction are very weak. So, the molecules of a gas are free to move about in the entire space available to them. That is why a gas neither has a fixed volume nor a fixed shape. |
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| When a gas is heated, the random motion of the molecules increases. This increases the rate of collision and as a consequence, increases the pressure exerted by the gas on the walls of the container. |
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| The kinetic theory of gases attempts to develop a model of the molecular behavior, which should result in the observed behavior of an ideal gas. |
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