Balanced chemical reaction: A + 5C ⇄ AC₅. <span>[A] = 0.100 M; equilibrium concentration. </span><span>[C] = 0.0380 M. </span>[AC₅] = 0.100 M. Kf = [AC₅] / ([A] · [C]⁵). Kf = 0.100 M ÷ (0.100 M · (0.0380 M)⁵. Kf = 12620658.54 = 1,26·10⁷. <span>The formation constant can be calculated when </span>chemical equilibrium is reached, when the forward reaction rate is equal to the reverse reaction rate.