What is the ideal gas equation?

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 m³ is:

1 m³ = 1000 dm³ = 1,000,000 cm³

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