Ideal gas law

From Wikipedia, the free encyclopedia

Isotherms of an ideal gas

The ideal gas law is the equation of state of an ideal gas. The state of an amount of gas is determined by its pressure, volume, and temperature. The equation has the form

$\ pV = nRT$

where

$\ p$ is the pressure [Pa],

$\ V$ is the volume [m³],

$\ n$ is the number of moles of gas [mol],

$\ R$ is the gas constant 8.314472 [m³·Pa·K^-1·mol^-1], and

$\ T$ is the temperature in kelvin [K].

The ideal gas constant ("R") is dependent on what units are used in the formula. The value given above, 8.314472, is for the SI units of Pascal-Meters³ per mole-Kelvin. Another value for R is .0821 L atm mol^-1 K^-1)

The ideal gas law is the most accurate for monatomic gases and is favored at high temperatures and low pressures. It does not factor in the size of each gas molecule or the effects of intermolecular attraction. The more accurate Van der Waals equation takes these into consideration.

1 Alternate Forms
2 Proof
- 2.1 Empirical
- 2.2 Theoretical
3 See also

[edit] Alternate Forms

Considering that the number of moles ( $n$ ) could also be given in mass, sometimes you may wish to use an alternate form of the ideal gas law. This is particularly useful when asked for the ideal gas law approximation of a known gas. Consider that the number of moles ( $n$ ) is equal to the mass ( $m$ ) divided by the molar mass ( $M$ ), such that:

$n = {\frac{m}{M}}$

Then, replacing $n$ gives:

$\ pV = {\frac{mRT}{M}}$

In thermodynamics and physics, when something is referred to as specific, it simply means the value per unit mass. In the case of the gas constant, the specific gas constant ( $r$ ) would be $R$ divided by the molar mass of the gas in question: