Extent of Reaction
A single variable measuring how far a reaction has progressed from pure reactants towards products.
Formula / equation
ξ = (n_i − n_i°) / ν_i
Unit
mol
In depth
Because the extent is divided by each species' stoichiometric coefficient, it takes the same value however it is calculated, giving one number that describes the whole system. Equilibrium corresponds to the extent at which the Gibbs energy reaches its minimum.
Examples in the real world
An extent of 0.4 mol in N₂ + 3H₂ ⇌ 2NH₃ means 0.4 mol of N₂ consumed and 0.8 mol of NH₃ formed.