The gas laws are a set of laws that describe the relationship between thermodynamic temperature (T), pressure (P) and volume (V) of gases. It is a loose collection of rules developed between the late Renaissance and early 19th century.

Ideal gases

Three earlier gas laws - Boyle's law (1662), Charles's law (1787-1802), and Gay-Lussac's law (1809) - were combined to form the combined gas law:

$\backslash frac\; \{P\_1V\_1\}\; \{T\_1\}\; =\; \backslash frac\; \{P\_2V\_2\}\; \{T\_2\}$

which with the addition of Avogadro's law later gave way to the ideal gas law:

$\backslash qquad\backslash qquad\; P\; V\; =\; n\; R\; T$

where

• P is the pressure in Pascal
• V is the volume in Cubic metres
• n is the number of moles of gas
• R is the ideal gas constant (8.31 J/mol K)
• T is the temperature in kelvins.

(The above units are the SI ones. The law works equally well with any consistent set of units, provided that the temperature scale is such that it is zero at absolute zero.)

Other important gas laws include Dalton's law of partial pressures. The kinetic theory of gases, Graham's law of effusion and root mean square velocity all explain how individual molecules in a gas act and their relation to pressure, volume, and temperature.

A gas that obeys these gas laws exactly is known as an ideal gas (or perfect gas). An ideal gas does not exist; however, some gases follow the laws more closely than others given standard conditions.

Non-ideal gases

Other gas laws, such as van der Waals equation, seek to correct the ideal gas laws to reflect the behaviour of actual gases. The van der Waals equation alters the ideal gas law to reflect how actual gases function using a series of calculated values called van der Waals constants.

It is also possible to apply Boltzmann's analysis to determine further information about gases.

See also

• Gas
• Laws of thermodynamics
• Equation of state

References

Gas laws | Gases

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