Notes: Chemistry In The Community

Kinetic Molecular Theory
The experimental observations about the behavior of gases discussed so far can be explained with a simple theoretical model known as the kinetic molecular theory. This theory is based on the following postulates, or assumptions.
Gases are composed of a large number of particles that behave like hard, spherical objects in a state of constant, random motion.
These particles move in a straight line until they collide with another particle or the walls of the container.
These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space.
There is no force of attraction between gas particles or between the particles and the walls of the container.
Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container.
The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.
The kinetic theory of gases describes a gas as a large number of small particles (atoms or molecules), all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container. Kinetic theory explains macroscopic properties of gases, such as pressure, temperature, or volume, by considering their molecular composition and motion. Essentially, the theory posits that pressure is due not to static repulsion between molecules, as was Isaac Newton's conjecture, but due to collisions between molecules moving at different velocities.
While the particles making up a gas are too small to be visible, the jittering motion of pollen grains or dust particles which can be seen under a microscope, known as Brownian motion results directly from collisions between the particle and gas molecules. As pointed out by Albert Einstein in 1905, this experimental evidence for kinetic theory is generally seen as having confirmed the existence of atoms and molecules.
Boyle's Law
 (sometimes referred to as the Boyle-Mariotte law) is one of many gas laws and a special case of the ideal gas law . Boyle's law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system. A law stating that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature.
Boyle's law explains an inverse relationship between the volume and pressure of a gas. For example, if the volume of a gas doubled, the pressure it exerted would be cut by half. If the volume tripled, the pressure would be a third of what it was before.
Boyle's law is used to predict the result of introducing a change, in volume and pressure only, to the initial state of a fixed quantity of gas. The before and after volumes and pressures of the fixed amount of gas, where the before and after temperatures are the same (heating or cooling will be required to meet this condition), are related by the equation:

Charles's law (also known as the law of volumes) is an experimental gas law which describes how gases tend to expand when heated the volume V of given mass of a gas is directly proportional to its absolute temperature.Charles studied the compressibility of gases nearly a century after Boyle. In his experiments he observed "At a fixed pressure, the volume of a gas is proportional to the temperature of the gas." Charles' Law describes the direct relationship of temperature and volume of a gas. Assuming that pressure does not change, a doubling in absolute tempature of a gas causes a doubling of the volume of that gas. A drop of absolute temperature sees a proportional drop in volume.The law can also be usefully expressed as follows:

The expression Gay-Lussac's law which concern the properties of gases, though it is more usually applied to his law of combining volumes, the first listed here. One law relates to volumes before and after a chemical reaction while the other concerns the pressure and temperature relationship for a sample of gas.
The law of combining volumes states that, when gases react together to form other gases, and all volumes are measured at the same temperature and pressure:The ratio between the volumes of the reactant gases and the products can be expressed in simple whole numbers.