Examkin

Question

Difficulty: EasyEquilibrium Constant Expression and Calculations

What is the correct equilibrium constant expression, KcK_c, for the reaction 2NO2(g)⇌N2O4(g)2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g)?

  1. Kc=[N2O4][NO2]2K_c = \frac{[\text{N}_2\text{O}_4]}{[\text{NO}_2]^2}Answer
  2. B
    Kc=[NO2]2[N2O4]K_c = \frac{[\text{NO}_2]^2}{[\text{N}_2\text{O}_4]}
  3. C
    Kc=[N2O4]2[NO2]K_c = \frac{[\text{N}_2\text{O}_4]}{2[\text{NO}_2]}
  4. D
    Kc=2[NO2][N2O4]K_c = \frac{2[\text{NO}_2]}{[\text{N}_2\text{O}_4]}

Answer

The correct equilibrium constant expression is Kc=[N2O4][NO2]2K_c = \frac{[\text{N}_2\text{O}_4]}{[\text{NO}_2]^2}.
According to the Law of Mass Action, the equilibrium constant expression KcK_c for a general reversible reaction aA+bB⇌cC+dDaA + bB \rightleftharpoons cC + dD is given by Kc=[C]c[D]d[A]a[B]bK_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}. For the reaction 2NO2(g)⇌N2O4(g)2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g), the concentration of the product N2O4\text{N}_2\text{O}_4 is raised to the power of 1 in the numerator, and the concentration of the reactant NO2\text{NO}_2 is raised to the power of 2 in the denominator, yielding Kc=[N2O4][NO2]2K_c = \frac{[\text{N}_2\text{O}_4]}{[\text{NO}_2]^2}.

Step-by-Step Solution

1
Identify the products and reactants along with their stoichiometric coefficients from the balanced equation.
Reactant: NO2\text{NO}_2 with coefficient 2; Product: N2O4\text{N}_2\text{O}_4 with coefficient 1.
Equilibrium constant expressions require product concentrations in the numerator and reactant concentrations in the denominator, each raised to the power of its stoichiometric coefficient.
2
Formulate the equilibrium constant ratio Kc=[Products]coefficients[Reactants]coefficientsK_c = \frac{[\text{Products}]^{\text{coefficients}}}{[\text{Reactants}]^{\text{coefficients}}}.
Kc=[N2O4]1[NO2]2K_c = \frac{[\text{N}_2\text{O}_4]^1}{[\text{NO}_2]^2}.
Placing [N2O4][\text{N}_2\text{O}_4] in the numerator and [NO2]2[\text{NO}_2]^2 in the denominator satisfies the law of mass action.

Key Concept

Equilibrium Constant Expression (KcK_c)
Rate this question

Topics

Equilibrium Constant Expression and Calculations