For a reaction A₂+B₂ ⇄ 2AB, the value of the equilibrium constant is calculated based on the concentrations of reagents and products in the equilibrium state:

K_c=[AB]²/[A₂][B₂].

In the case of diagramme 3, [AB]=6[A₂]=6[B₂]=6c and consequently the value is: K_c=(6c)²/c.c= 36