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Introduction of Gaseous State
We can survive for weeks without food, days without water, but only minutes without air. Thus, we inhale a lungful of air every few seconds, keep some of the molecules for our own end, and some of the molecules that our body no longer needs, and exhale the mixture back into the surrounding air. The air around us is in the gaseous state, which is the simplest of the states of matter.
Although the chemical behaviour of gases depends on their composition, all the gases have remarkably similar physical behaviour. Earth is surrounded by an atmosphere of air whose composition in volume percentage is roughly 78 % nitrogen, 21 % oxygen and 1 % other gases. Of the known elements, only eleven are gases under normal atmospheric conditions. The elements hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2) and chlorine (Cl2) exist as gaseous diatomic molecules.
Another form of oxygen, namely, ozone (O3) is also a gas at room temperature. The noble gases, namely, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn) of 18th group are monatomic gases. Compounds such as carbon monoxide (CO), carbon dioxide (CO2), nitrogen dioxide (NO2) and nitric oxide (NO) also exist in gaseous state under normal atmospheric conditions. In this unit you will learn the properties of gases and other related phenomena.
Gaseous State is the simplest state of matter. In fact, the lowermost part of the atmosphere (called troposphere) in which we live is a mixture of gases like Dioxygen, Dinitrogen, Carbon Dioxide, Water Vapour etc.
The state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container.
They do not have definite shape and take up the shape of the container. They do not possess definite volume due to weakest intermolecular forces. They are not rigid. They are easily compressible due to excess space between the particles of gas which compresses on applying pressure.
Gases have a lower density and are highly compressible as compared to solids and liquids. They exert an equal amount of pressure in all directions.
The space between gas particles is a lot, and they have high kinetic energy.
Gases have three characteristic properties:
- They are easy to compress
- They expand to fill their containers, and
- They occupy far more space than the liquids or solids from which they form.
The gas constant is a physical constant denoted by R and is expressed in terms of units of energy per temperature increment per mole. It is also known as Ideal gas constant or molar gas constant or universal gas constant.
The density of gases are much larger than those of corresponding liquids. It is not a property of gases. Density is equal to mass divided volume. Since gases have larger volumes, their densities are lower than those corresponding to liquids.
Molecules within gases are further apart and weakly attracted to each other. Heat causes the molecules to move faster, (heat energy is converted to kinetic energy) which means that the volume of a gas increases more than the volume of a solid or liquid.
