5 of 5

Write now Article Tools

The equation of ideal (perfect) gas at low pressure was established by combining a series of empirical laws like Boyle's law, Charles Gay-Lussac law and Avogadro's principle.

It helpful to picture ideal gas as a collection of molecules (or atoms) in continues random motion, with speeds that increase of temperature is raised. During collisions the molecules of a gas are widely separated from one another and move in paths that are largely unaffected by intermolecular forces. Only that gas can by ideal (perfect) gas.

Boyle's law

Robert Boyle, acting on the suggestion of a correspondent John Townley, showed in 1661:

P x V=constant

P-pressure
V-volume

Th at is, at constant temperature, the pressure is inversely proportional to its volume, and the volume it is inversely proportional to its pressure.

The experiment have shown that Boyle's low is valid only at low pressures and is an example of a limiting law, a law that is strictly true only in a certain limit, in this case p0.

Charles's Gay - Lussac's law

Jacques Charles and Joseph Gay-Lussac found independently that volume increased linearly with the temperature.

V = constant x T (at constant pressure)

V-volume
T-temperature

Alternative version in which the pressure of gas falls to zero as the temperature is reduced to zero.

P = constant x T (at constant volume)

P-pressure
T-temperature

Avogadro's principle

The modern form of Avogadro's principle is that equal volumes of gases at the same pressure and temperature contain the same numbers of molecules.

V = constant x n (at constant pressure and temperature)

V-volume
n-content matter

Avogadro's principle is not law because it depends on the validity of a model, in this case the existents of molecules.

Combination of the two laws and principle gives single expression:

P x V = n x R x T

P-pressure
V-volume
n-content matter
R-gas constant
T-temperature

This expression is known like ideal (perfect) gas equation. R is known like gas constant and can be determined by evaluating for gas in the limit of zero pressure (to guarantee that it is behaving perfectly).

R = P x V / n x T

The perfect gas equation is of the greatest importance in physical chemistry because it is used to derive a wide range of relations that are used throughout thermodynamics.

Used literature:

P. Atkins and J. de Paula, Atkins's Physical Chemistry, Oxford University Press, Seventh Edition, 2002.

Learn more about this author, Lady Write.
Click here to send this author comments or questions.

Add your voice

Know something about The ideal gas law?
We want to hear your view. Write now!