Boyle's law | Robert Boyle | Gas Law | Home revise
In the year 1662, Robert Boyle stated that at constant temperature, the volume of a fixed
mass of a gas decreased by half when the pressure on it was doubled, and it became four times
its original volume when its pressure was decreased by one-fourth.
He described this behavior in the form of a law, known as Boyle's Law.
The volume of a given mass of a dry gas is inversely proportional to its pressure at
constant temperature.
Mathematical expression of Boyle's Law Suppose a gas occupies a volume V1 when its
pressure is P1, then V1 is inversely proportional to P1 or V1 is equal to k upon P1 or P1V1
is equal to k which is equal to a constant.
If V2 is the volume occupied when the pressure is P2 at the same temperature, then V2 is
inversely proportional to P2 or V2 is equal to k upon P2 or P2V2 is equal to k is equal
to constant.
Therefore, P1V1 is equal to P2V2 is equal to k at constant temperature.
This is called Boyle's Law equation.
Boyle's Law may also be stated as, the product of the volume and pressure of a given mass
of a dry gas at a constant temperature is constant.
Graphical Representation of Boyle's Law The law can be verified by plotting a graph.
First, V versus 1 upon P. Second, V versus P. Third, PV versus P. First, V versus 1 upon
P. A straight line passing through the origin is obtained, as seen in the figure.
Second, V versus P. A hyperbolic curve in the first quadrant is obtained, as seen in
the figure.
Note, the term isotherm meaning at constant temperature is used to describe these plots.
Third, PV versus P. A straight line is obtained parallel to the pressure axis, as seen in
the figure.
Significance of Boyle's Law On increasing pressure, volume decreases.
The gas becomes more dense.
Thus, at constant temperature, the density of a gas is directly proportional to its pressure.
Atmospheric pressure is low at high altitudes, so air is less dense.
Hence, a lesser volume of oxygen is available for breathing.
This is the reason why mountaineers have to carry oxygen cylinders with them.