| | Doubling the number of particles will double the volume of a gas. So: | | **V = constant**_{5}.N | | at constant T and P | | | | N is the number of particles | | If we combine these last two equations, we get: | | **p.V = N.k.T ** | | N is the number of molecules; k is a special constant called the Boltzman constant. It has the value: 8.31 J K^{-1} | And in moles . . | A mole of gas has 6.0 x 10^{23 }particles (this is the Avogadro number, N_{A}). So, for n moles of a gas, we can say that: | | **p.V = n.R.T** | | Where n is the number of moles; R is the molar gas constant. It has the value: 1.38 x 10^{–23 }J K^{–1} mol^{-1} | | | | This is the **ideal gas equation**. |