If concentration of N₂,H₂ and NH₃ are 1, 2 and 3 respectively, their concentrations at equilibrium will be:
${\mathrm{N}}_2+3{\mathrm{H}}_2\rightleftharpoons 2{\mathrm{NH}}_3$

$\underset{\left(1-\mathrm{x}\right)}{\underset{1}{{\mathrm{N}}_2}}+\underset{(2-3\mathrm{x})}{\underset{2}{3{\mathrm{H}}_2}}\rightleftharpoons \underset{\left(3+2\mathrm{x}\right)}{\underset{3}{2{\mathrm{NH}}_3}} \underset{: \mathrm{After} \mathrm{reaction}}{\underset{:\mathrm{Before} \mathrm{reaction}}{{ }_{ }}}$
x mole of N₂ will react with 3x mole of H₂ to give 2x mole of NH₃. Notice the stoichiometry of change.