What is Gas?
Gas is one of three states of matter, with the other two being solid and liquid. According to the Kinetic Molecular Theory, gases consist of molecules with negligible sizes when compared with the distance between each of them. And since the molecules are so small, attraction or repulsion forces are also negligible and weak, except only when these particular molecules go into collision.

There are many properties that are characteristic to gases. One such property is compressibility. Gases are known to be easily compressed compared to solids and liquids. Even when pressure is added, the gas mass will remain constant. Another property is expandability. A typical demonstration of this property is when a person cooks in the kitchen. Vapors will come out from the cooking pot and the smell will fill the entire room. Gases also occupy far greater space than solids and liquids.

A particular gas can also be mixed with other types of gasses through effusion or diffusion. In diffusion, a gas mixes with other gases in a container as it enters the said container. An example of this process is when an ammonia bottle is opened and its smell will immediately mix with the air in the room. Effusion meanwhile happens when a particular gas moves from one container to another. Like when a small hole is punched through the crown of a softdrink bottle, small amounts of gas will escape to the atmosphere.

Gases are also said to have lower density because molecules and atoms are arranged more loosely compared to solids and liquids, which have more compact molecular structure. Applying heat or cold meanwhile will change the behavior of the molecules in gas. When subjected to increased temperatures, the molecules and/or atoms of gas will gain kinetic energy and will move rapidly. The opposite will result if the same gas is cooled. Some gases even transform to become solid or liquid when subjected to extremely low temperatures. An example of which is nitrogen, wherein this gas will become liquid if cooled to below zero degrees Centigrade.