Gas laws

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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.

1 Ideal gases
2 Non-ideal gases
3 See also
4 References

[edit] Ideal gases

Three earlier gas laws:

Boyle's law (1662, relating pressure and volume),
Charles's law (1787, relating volume and temperature), and
Gay-Lussac's law (1809, relating pressure and temperature),

were combined to form the combined gas law

$\frac {P_1V_1} {T_1} = \frac {P_2V_2} {T_2}.$

With the addition of Avogadro's law, this gave way to the

ideal gas law

$PV = nRT \,$ ,

where

P is the pressure (SI unit: pascal)

V is the volume (SI unit: cubic meter)

n is the number of moles of gas

R is the ideal gas constant (SI: 8.3145 J/(mol K))

T is the thermodynamic temperature (SI unit: kelvin).

(The law works with any consistent set of units, provided that the temperature scale is zero at absolute zero, and the proper gas constant is used.)

An equivalent formulation of this law is:

$PV = NkT \,$

where

N is the number of molecules

k is the Boltzmann constant.

These equations are exact only for an ideal gas, which is a fictional construct. However, the ideal gas laws are good approximations for many gases under many circumstances.

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. Dalton's law of partial pressures, another important gas law, explains the behavior of mixtures of gases.

This law has the following important consequences:

If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
If the temperature and volume remain constant, then the pressure of the gas changes is directly proportional to the number of molecules of gas present.
If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature.

Gases and fluids flow from regions of high pressure to regions of low pressure.

[edit] 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.

[edit] See also

[edit] References

Castka, Joseph F.; Metcalfe, H. Clark; Davis, Raymond E.; Williams, John E. (2002). Modern Chemistry. Holt, Rinehart and Winston. ISBN 0-03-056537-5.
Guch, Ian (2003). The Complete Idiot's Guide to Chemistry. Alpha, Penguin Group Inc.. ISBN 1-59257-101-8.
Zumdahl, Steven S (1998). Chemical Principles. Houghton Millfin Company. ISBN 0-395-83995-5.