Kinetic theory of gases

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KINETIC THEORY OF GASES

The Kinetic theory of gases refers to the mo-tions of gases. Gases consist of molecules that have no inherent tendency to stay in one place as do the molecules of a solid. Instead, the molecules of gas, since they are smaller than the space between them, are free to move about. The mo-tion is in straight lines until the lines collide with each other or with other obstructions, making their overall motion random. When a gas is enclosed, its pressure depends on the number of times the molecules strike the surrounding walls. The number of blows that the molecules strike per second against the walls remains constant as long as the temperature and the volume remain constant. If the volume (the space occupied by the gas) is decreased, the number of blows against the wall is increased, thereby increasing the pressure if the temperature remains constant. Temperature is a measure of the molecular activity of the gas molecules and a measure of the internal energy of a gas. When the temperature is increased, there is a corresponding increase in the speed of the molecules; they strike the walls at a faster rate, thereby increasing the pressure provided the volume remains constant.

Therefore, there is a close relationship of volume, pressure, and density of gases.

BOYLE’S LAW

Boyle’s law states that the volume of a gas is inversely proportional to its pressure, provided the temperature remains constant. This means that if the volume is halved, the pressure is doubled. An example of Boyle’s law is a tire pump. As the volume of the pump’s cylinder is decreased by pushing the handle down, the pressure at the noz-zle is increased. Another way of putting it is, as you increase the pressure in the cylinder by pushing down the handle, you also decrease the volume of the cylinder. The formula for Boyle’s law is as follows:

For example, assume 20 cm3 of gas has a pressure of 1,000 mb. If the pressure is increased to 1,015 mb and the temperature remains con-stant, what will be the new volume? Applying the formula, we have

Boyle’s law does not consider changes in temperature. Since our atmosphere is constantly changing temperature at one point or another, temperature must be considered in any practical application and understanding of Gas Laws.

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