This law states that the volume of a given mass of gas is inversely proportional to its pressure provided that temperature remains constant.

where k is a constant, P and V being the pressure and volume of the gas respectively. This law was verified using the apparatus shown in the Figure below.

**Experimental**

Robert Boyle (1627 -1691) worked on gases using J -shaped glass tubes. He entrapped a sample of air in the closed end of the tube with the aid of mercury. When he added more mercury to the longer opened end, the air was compressed to a smaller volume, but when he decreased the mercury thread, the air expanded to a greater volume. On measuring the air volume corresponding to the varying pressure, he observed a simple relationship between pressure and volume of the gas.

**Boyle’s law apparatus**

The longer the column of mercury h the more compressed the air and hence the higher the pressure. The results of the experiment are shown in the Table below.

The results indicate that the product of the volume of air and pressure exerted is nearly constant giving a straight line passing through the origin which can be expressed as:

**Graphical representation of Boyle’s law**

**Boyle’s Law Explained by Kinetic Theory**

The conditions in A, B, and C can be created as shown below.

– In A, pressure P is caused by the number of collisions of the gas molecules on the walls of the vessel.

– In B, the volume of the container is doubled. The gas molecules have a large space to move in therefore the number of collisions is halved.

– In C, the volume in A is reduced by half. The gas molecules have a very small space to move in therefore the collision on the walls of the vessel will increase thus increasing pressure.

**Diagrammatic representation of Boyle’s law**

Boyle’s law states that the volume V of a given mass of gas is inversely proportional to its pressure P, provided temperature remains constant.