Introduction
Gas is one of the three states of matter - the other two being liquid and solid. A gas differs from a solid and a liquid in a number of ways. A gas fills entire space available to it and therefore it has no definite shape or volume.
History
In the beginning of the 17th century, scientists started realising that some form of matter can exist in a form that is similar to air. The Belgian Chemist Jan Baptista van Helmont coined the word Gas by altering the Greek word "Chaos" which means "Space". This word explains the ability of a gas to fill any amount of space.
Characteristic Properties of a Gas
Gases do not posses any definite shape or volume. They will completely fill all the space available to them. The tendency of a gas to fill the available volume within a container is the result of the freedom that gas particles have to move everywhere in the available space. This freedom of movement of gaseous molecules is due to very weak binding forces between molecules. In other words their intermolecular forces are very weak. Because of this the molecules of gas are in a continuous motion and are associated with high velocity and therefore high kinetic energy.
Gas behavior
All gases, irrespective of their chemical composition, obey certain laws that govern the relationship between the volume, temperature and pressure of the gases. A given mass of a gas, under definite conditions of temperature and pressure, occupies a definite volume. When any of the three variables is altered, then the other variables get altered. Thus these Gas laws establish relationships between the three variables of volume, pressure and temperature of a gas.
Behavior of Gases Under Varying Conditions of Pressure and Temperature
When temperature remains constant, the volume of a fixed mass of a gas decreases as the pressure increases, and it increases when the pressure decreases. There is an inverse relationship between pressure and volume.
Properties of Gases in Terms of Molecular Motion
Gases, as well as mixture of gases, behave as seen above, with regard to changes in temperature, pressure or both.
Gas Laws - Boyle's Law
The volume of a given mass of a dry gas is inversely proportional to its pressure, temperature remaining constant. Robert Boyle (1627 - 1691) discovered this law in 1662 and it was named after him.
Problems Based on Boyle's Law
A given mass of a gas occupies 240 ml at 800 mm of Hg. What volume will the gas occupy if the pressure is increased to 1200 mm of Hg, temperature remaining constant?
Gas Laws - Charle's Law
Jacques Alexander Cesar Charles, a French chemist, discovered in 1787, that at a constant pressure, with rise in temperature, carbon dioxide, hydrogen, oxygen and nitrogen, all expanded at constant rates.
Problems Based on Charle's Law
A given mass of a gas occupies 960 ml at 27oC. What volume will it occupy if the temperature is raised to 177oC, pressure remaining constant.
Standard Temperature and Pressure
The volume of a given mass of a gas changes directly with temperature and inversely with pressure. Volumes can be rationally compared only if they are at a certain fixed conditions of temperature and pressure. By convention, standard temperature and pressure condition (STP) for volumes of gases have been accepted as 0oC (273 K) and 1 atmospheric pressure (76 cm or 760 mm of mercury).
The Gas Equation
According to Boyle's Law, the volume of a gas varies inversely as the pressure, temperature remaining constant, i.e.,
Problems Based on Gas Equation
A gas occupies 500 ml at 40oC and 800 mm pressure. What volume will it occupy at 353oC and 600 mm pressure?
Summary
Gases are different from solids and liquids. They have no definite shape or volume.
