kinetic-molecular theory of gases


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kinetic-molecular theory of gases,

physical theory that explains the behavior of gases on the basis of the following assumptions: (1) Any gas is composed of a very large number of very tiny particles called molecules; (2) The molecules are very far apart compared to their sizes, so that they can be considered as points; (3) The molecules exert no forces on one another except during rare collisions, and these collisions are perfectly elastic, i.e., they take place within a negligible span of time and in accordance with the laws of mechanics. A gas corresponding to these assumptions is called an ideal gas; as the temperature of a real gas is lowered, or its pressure is raised, its behavior no longer resembles that of an ideal gas because one or more of the assumptions of the theory is no longer valid. The analysis of the behavior of an ideal gas according to the laws of mechanics leads to the general gas law, or ideal gas law: The product of the pressure and volume of an ideal gas is directly proportional to its absolute temperature, or PV = kT (see gas lawsgas laws,
physical laws describing the behavior of a gas under various conditions of pressure, volume, and temperature. Experimental results indicate that all real gases behave in approximately the same manner, having their volume reduced by about the same proportion of the
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). Boyle's law, Charles's law, and Gay-Lussac's law, which are special cases of the general gas law, may also be easily derived. The theory further shows that the absolute temperature is directly proportional to the average kinetic energy of the molecules, thus providing an interpretation of the nature of temperature in general in terms of the detailed structure of matter (see temperaturetemperature,
measure of the relative warmth or coolness of an object. Temperature is measured by means of a thermometer or other instrument having a scale calibrated in units called degrees. The size of a degree depends on the particular temperature scale being used.
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; Kelvin temperature scaleKelvin temperature scale,
a temperature scale having an absolute zero below which temperatures do not exist. Absolute zero, or 0°K;, is the temperature at which molecular energy is a minimum, and it corresponds to a temperature of −273.
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). Pressure is seen to be the result of large numbers of collisions between the molecules and the walls of the container in which the gas is held. See thermodynamicsthermodynamics,
branch of science concerned with the nature of heat and its conversion to mechanical, electric, and chemical energy. Historically, it grew out of efforts to construct more efficient heat engines—devices for extracting useful work from expanding hot gases.
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.