Gases

What's a gas, you say? A gas is usually in the shape of an ever expanding cloud. Gas molecules are mostly independent particles traveling at lightning speeds. You can't describe gases like liquids or solids. Gases are often colorless, they have no set shape or volume. There are three properties, however that all gases have in common:

Expansion- a gas has neither a definite form nor volume; rather it continuously grows to fill whatever container it is in.

Pressure- an inflated balloon may burst from the force that the air inside exerts on its inside surface. This force is caused by the constant bombardment of billions of gas molecules against the balloon. If you increase the number of molecules, the number of collisions increases, the pressure increases, and the balloon inflates.

Diffusion- when one type of particle mixes with a particle of another kind. Example: Let's say you have two bottles mouth-to-mouth, standing upright. In the top bottle you have a very light gas, in the bottom, a very heavy gas. Through diffusion the 2 gases will mix and interact.

When you get vapor or gas from matter that was in another state, that's vaporization. If you had some ether in a dish, in time the amount of liquid would decrease, and you would be able to smell the ether in the air. The reason for this is, molecules of liquid ether become molecules of ether gas. These molecules mix with the surrounding air. In the same way, mothballs that are left out too long will eventually disappear. The smell will be in the air, however. In this case, the solid mothballs convert directly into a gaseous form. These two examples illustrate the two forms of vaporization, evaporation and sublimation. Evaporation occurs when a liquid turns into a gas. Sublimation is the process where solids change into gas.

The energy needed for the molecules to change phase is supplied by the air around them. In either case, evaporation has a cooling effect on the environment. When sweat evaporates from the skin, the skin gets cool. When rubbing alcohol is used the effect is much greater, because alcohol evaporates much faster than water. Since the speed of vaporization depends on the energy of the particles going through the change, and their energy depends on the temperature, vaporization occurs faster at higher temperatures, and slower at lower temperatures.

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