At equilibrium the concentrations of reactants and products can be predicted using the equilibrium constant, K which is a mathematical expression based on the chemical equation. For example, in the reaction aA + bB cC + dD where a, b, c, and d are the stoichiometric coefficients, the equilibrium constant is K_c = [C]^c [D]^d/[A]^a[B]^b where [A], [B], [C], and [D] are the equilibrium concentrations. If the reactions in not at equilibrium, the quantity can still be calculated, but it is called the reaction quotient, Q_c, instead of the equilibrium constant, K_c. Q_c = Where each concentration is measured at some arbitrary time t. A mixture initially contains A, B, and equilibrium, the concentrations of reactants and C in the following concentrations [A] = 0.555 M, [B] = 0.650 M, and [C] = 0.700 M. The following reaction occurs and equilibrium is established. A + 2B C At equilibrium, [A] = 0.390 M and [C] = 0.860 M. Calculate the value of the equilibrium constant, K_c. Express your answer numerically.