As the air has little weight for large amount of volume it makes, things filled with it to float on the
water. This property of gas will be used in tubing and helps people afloat in water.
We breathe air. We feel a breeze blowing over our body. We feel the temperature of air. But with all this familiarity with air around us, we get very little idea about what is air, or why it behaves the way it does. Behavior of gases could be studied with thermodynamics.
Behavior of gases:
Gases behave differently when compared to liquids and
solids. This may be due to their low weight which is
due to large volume occupancy, less intermolecular
forces etc., Let us discuss how a gas behaves when
it is subjected to the external changes.
Snow shoes allow us to walk on powdery snow without sinking because of distribution of weight over much
larger area than our feet there by greatly decreasing the pressure per square inch. For the same reason high heels exert more
pressure than normal flat shoes.
Relation with pressure:
When a sample of gas is confined to a container
which has a variable volume (such as balloon, piston)
an external force applied will compress the gas resulting
in lower volume. By removing the external pressure the
container retains its original shape leading to the
increase in volume of gas. This kind of variation of
volume will be less appreciated in case of solids and liquids.
Effect of temperature
When liquid nitrogen is poured on the balloon the gas in the balloon is cooled and its volume decreases.
When a gas at a constant pressure is subjected to heat, its volume increases.
Relation with temperature:
When a gas at a constant pressure is subjected to heat,
its volume increases; when cooled, its volume decreases.
This dependence on temperature is 100 times more pronounced
in the case of gases when compared to the liquids or solids.
Densities:
Gases will have low density as they occupy large volume
for very little mass. As density is inversely proportional
to volume, more the volume less is the density if mass is kept
constant. It is usually tabulated in units of grams per liter, whereas
it is grams/milli liter in case of solids and liquids which are about
1000 times denser than gases.
E.g.: Density of O2 gas at 20°C and normal atmospheric pressure is 1.3 g/L, where as density of water (H2O) is 1.0 g/mL.