Final answer:
In a chemical reaction where the equilibrium constant is much less than 1, the concentration of the reactants is much greater than that of the products at equilibrium. A catalyst has no effect on the concentrations at equilibrium. Therefore, the correct answer is that the reactant concentration is much greater than the product concentration at equilibrium.
Step-by-step explanation:
When analyzing a gas phase reaction like COCl₂ → CO+Cl₂ with a equilibrium constant (Kc) much less than 1, it indicates a low ratio of product concentrations to reactant concentrations at equilibrium. This means that the reaction favors the formation of reactants rather than products. Consequently, at equilibrium, the concentration of reactant is much greater than the concentration of products.
Reflecting further on this concept, when Kc is less than 10⁻³, chemists often say the equilibrium lies to the left, favoring the formation of reactants. A catalyst does not affect the concentrations of reactants or products at equilibrium; it merely speeds up the rate at which equilibrium is reached.
Therefore, for a reaction where Kc is much less than 1, option d is correct: The concentration of reactant is much greater than the concentration of products at equilibrium.