mE + nF -----> pG + qH  In the equation shown, the equilibrium constant is given by?

Analysis of the Question

This question tests your understanding of the Law of Mass Action as it applies to chemical equilibrium. You are asked to derive the expression for the equilibrium constant ($K_c$) for a general reversible chemical reaction.

Concept Explanation

The equilibrium constant ($K_c$) for a reversible reaction is defined as the ratio of the product of the concentrations of the products to the product of the concentrations of the reactants, with each concentration raised to the power of its stoichiometric coefficient from the balanced chemical equation.

For a general reaction:

The equilibrium constant expression is:

• [ ] represents the molar concentration of the species.
• The letters a, b, c, and d are the stoichiometric coefficients (the numbers in front of the chemical formulas).

Step-by-Step Solution

1. Identify the products and reactants: In the equation $mE + nF \rightleftharpoons pG + qH$, the products are G and H, and the reactants are E and F.
2. Identify the coefficients: The coefficients are p and q for the products, and m and n for the reactants.
3. Apply the formula: • Place the products in the numerator: $[G]^p [H]^q$ • Place the reactants in the denominator: $[E]^m [F]^n$
4. Combine them: $$K_c = \frac{[G]^p [H]^q}{[E]^m [F]^n}$$

Comparing this result to your options, it matches option C.

Exam Tip

Always remember: "Products over Reactants." A common mistake students make is flipping the fraction or forgetting to raise the concentrations to the power of their coefficients. If you see a coefficient in the equation, it must appear as an exponent in your $K_c$ expression!