# What is the ideal gas equation?

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The ideal gas equation, pV = nRT, is an equation used to calculate either the pressure, volume, temperature or number of moles of a gas.

The terms are:

p = pressure, in pascals (Pa).

V = volume, in m3.

n = number of moles.

R = the gas constant, 8.31 J K-1 mol-1 (you will be given this value).

T = temperature, in kelvin (K).

In an exam question, you will be normally be given 4 of the terms and asked to work out the 5th. The equation can be rearranged to work out each of the different terms. For example, to calculate the number of moles, n:

pV = nRT is rearranged to n = RT/pV.

The hardest part of the question is often using the correct SI units, as given above. Often you will have to convert a term from the incorrect to the correct units before using it in the equation.

Pressure may be given in atmospheres or kPa, for which the conversions are:

1 atm = 101,325 Pa.

100 kPa = 100,000 Pa,

Temperature may be given in degrees celsius. To convert this to kelvin, you simply add 273.

Volume may be given in cm3 or dm3, for which the conversion to mis:

1 m3 = 1000 dm= 1,000,000 cm3

Once you have the terms in the correct SI units, you can simply plug them into your rearranged equation.

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