Moderate

For the reaction A + B ⇌ C + D, the equilibrium constant can be expressed as:

Correct answer: C. K=[C][D]/[A][B]

  • A. K= [A][B]/[C][D]
  • B. K=[C][B]/[A][D]
  • C. K=[C][D]/[A][B]
  • D. K=[A][C]/[B][D]

Explanation

The equilibrium constant expression for a reaction is written as the concentration of the products raised to the power of their stoichiometric coefficients divided by the concentration of the reactants raised to the power of their stoichiometric coefficients. For the reaction A + B ⇌ C + D, the correct expression for the equilibrium constant is K = [C][D]/[A][B], where [C] and [D] are the concentrations of the products and [A] and [B] are the concentrations of the reactants. Option C correctly reflects this relationship. The other options are incorrect because they either place reactant concentrations in the numerator or mix up products and reactants.

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About Chemical Equilibrium

Reversible reactions reach dynamic equilibrium when forward and reverse rates become equal, and Le Chatelier's principle predicts the effect of changing concentration, pressure or temperature. The chapter also covers solubility product, the common ion effect, buffer action and the conditions used in Haber's process, with equilibrium shifts distinguished from changes in the equilibrium constant.

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