Gas is one of the basic state of matter. The other fundamental states are solid and liquid. Gas have no definite shape nor size. Gases will occupy the whole space of a closed container. The properties of a gas is dependent on the volume of the container. Gases in a closed container tends to move rapidly .They move chaotically and randomly hitting the wall of the container. Gas have low density and are highly compressible. Gas moves rapidly due to the inter-molecular forces holding them is weak.
The forces holding them are weak and the molecules rarely interact they collide with each other constantly in a closed system. The molecules will escape immediately if the closed system is open because of the rapid nature of the molecules.
