Gases

According to the philosopher Anaximenes, matter exists from air. Gases are classified as the third physical state of matter. Like everything, each one is different from the rest and it has its own characteristics. The Kinetic Molecular Theory of Gases, postulates based from basic behaviors of atoms, attempts to explain the properties of gases. The Kinetic Molecular Theory, also called as the Collision Theory has the following postulates:

1. Gases are composed of atoms/molecules that are separated and far from one another. The space betweenn them is very wide, thus, occupying a wide space in the atmosphere.
2. These tiny particles are moving constantly in a straight path but random direction, resulting to the collision between them and with the walls of the container, thus, creating pressure.
3. The force of attraction between atoms is negligible.
   Collision of the particles does not result in the energy change, although a transfer of energy may occur in the collision.
4. All gas molecules have the same average kinetic energy at the same temperature. Temperature is defined as avergae kinetic energy. (Brown et al 2000 1)

From these postulates, we can then draw the following properties:

• Gases are compressible. Since gas molecules are from from each other, they can be compressed closer to decrease the gap between molecules.
• Gases have low densities. Since gas molecules are from from each other, they would occupy a greater space compared with the other states of matter. Gases would have lighter mass to keep moving at a particular speed. With a small value of mass, and occupying a big volume, the ration (density) would be low.
• Gases exert pressure. Gas molecules are constantly moving, hitting everything in its path thus creating pressure.
• Gases diffuse easily. Since gas molecules move constantly, it then travels from one place to another.
  Gases are affected by changes in temperature. (2)

Aside from the behavioral properties, gases also have the following measurable properties:

• Pressure (P). A measure of force applied on an object per unit area (P=F/A). Pressure in the atmosphere is caused by the weight of the air from the outer edge of the atmosphere down to the surface of the earth. Measurement of pressure was first introduced by Evangelista Toricelli.
• Temperature (T). The average kinetic energy. If a gas is to reach absolute zero (O Kelvin), its particles would have no energy or motion.
• Volume (V). Volume of a gas is equal to the volume of the container since a gas completely fills its container.
• Amount of gas (n). The amount of gas is measured in moles or number of particles.

Other properties:

• Diffusion. the process of spreading out of molecules to fill a space uniformly.
• Effusion. the process by which gas molecules spread out in an empty space through a small opening.