Write the expression for the equilibrium constant Kp for aA + bB ⇌ cC + dD.

Write the expression for the equilibrium constant Kp for aA + bB ⇌ cC + dD.

• A. Kp = (PA^a PB^b)/(PC^c PD^d)
• B. Kp = (PC^d PD^c)/(PA^a PB^b)
• C. Kp = (PC^c PD^d)/(PA^a PB^b)
• D. Kp = (PA^a PB^b PC^c PD^d)

Answer: (C)

The main idea is that Kp for a gas-phase reaction is the ratio of product partial pressures to reactant partial pressures, with each pressure raised to its stoichiometric coefficient. For aA + bB ⇌ cC + dD, this gives Kp = (PC^c PD^d)/(PA^a PB^b). The expression puts products in the numerator and reactants in the denominator, and the exponents match the coefficients, reflecting how much of each species participates at equilibrium. If a species were a pure solid or pure liquid, it would be omitted, but all species here are treated as gases. The other forms misplace the species or exponents or form a product of all four pressures, which does not represent the equilibrium ratio.

The main idea is that Kp for a gas-phase reaction is the ratio of product partial pressures to reactant partial pressures, with each pressure raised to its stoichiometric coefficient. For aA + bB ⇌ cC + dD, this gives Kp = (PC^c PD^d)/(PA^a PB^b). The expression puts products in the numerator and reactants in the denominator, and the exponents match the coefficients, reflecting how much of each species participates at equilibrium. If a species were a pure solid or pure liquid, it would be omitted, but all species here are treated as gases. The other forms misplace the species or exponents or form a product of all four pressures, which does not represent the equilibrium ratio.