At equilibrium, the concentrations of reactants and products can be predicted us

Question

At equilibrium, the concentrations of reactants and products can be predicted using the equilibrium constant, K_c, which is a mathematical expression based on the chemical equation. For example, in the reaction aA + bB Equilibrium 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 reaction is 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 = [C]_t^c[D]_t^d/[A]_t^a[B]_t^b where each concentration is measured at arbitrary time t. Part A A mixture initially contains A, B, and C in the following concentrations: [A] = 0.350 M, [B] = 0.700 M, and [C] = 0.450 M. The following reaction occurs and equilibrium is established: A + 2B Equilibrium C At equilibrium, [A] = 0.150 M and [C] = 0.650 M. Calculate the value of the equilibrium constant, K_c. Express your answer numerically. K_c = _______

Explanation / Answer

A        +   2B       <—>       C

0.350       0.700           0.450 (initial)

0.350-x   0.700-2x       0.450+x (at equilibrium)

At equilibrium,

[C] = 0.650 M

So,

0.450 + x = 0.650

x = 0.200 M

[B] = 0.700 - 2x = 0.700 - 2*0.200 = 0.300 M

Kc = [C]/[A][B]^2

   = (0.650) / {(0.150)*(0.300)^2}

   = 48.1

Answer: 48.1

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