[PDF] Equilibria: Kp Practice Questions and Answers

1. What is the equilibrium constant, Kc, a measure of? * A) The rate of the forward reaction. * B) The rate of the reverse reaction. * C) The position of equilibrium in terms of concentrations. * D) The activation energy of the reaction. 2. For the reaction aA + bB ⇌ cC + dD, what is the expression...

1. What is the equilibrium constant, Kc, a measure of? * A) The rate of the forward reaction. * B) The rate of the reverse reaction. * C) The position of equilibrium in terms of concentrations. * D) The activation energy of the reaction. 2. For the reaction aA + bB ⇌ cC + dD, what is the expression for Kc? * A) Kc = ([C]c[D]d) / ([A]a[B]b) * B) Kc = ([A]a[B]b) / ([C]c[D]d) * C) Kc = (cC + dD) / (aA + bB) * D) Kc = (aA + bB) / (cC + dD) 3. What are the units for K? * A) mol dm-3 * B) s-1 * C) J K-1 mol-1 * D) It depends on the stoichiometry of the reaction. 4. What does a large value of Kc (Kc >> 1) indicate? * A) The equilibrium lies to the left (reactants favored). * B) The equilibrium lies to the right (products favored). * C) The reaction is very fast. * D) The reaction is very slow. 5. What is the equilibrium constant, Kp, a measure of? * A) The position of equilibrium in terms of concentrations. * B) The position of equilibrium in terms of partial pressures. * C) The rate of the forward reaction. * D) The activation energy of the reaction. 6. For the reaction aA(g) + bB(g) ⇌ cC(g) + dD(g), what is the expression for Kp? * A) Kp = (pCcpDd) / (pApBb) * B) Kp = (pApBb) / (pCcpDd) * C) Kp = ([C]c[D]d) / ([A]a[B]b) * D) Kp = ([A]a[B]b) / ([C]c[D]d) 7. What is partial pressure? * A) The total pressure of a gas mixture. * B) The pressure exerted by an individual gas in a mixture. * C) The pressure exerted by the reactants in a reaction. * D) The pressure exerted by the products in a reaction. 8. How do you calculate the partial pressure of a gas in a mixture? * A) Partial pressure = mole fraction x total volume * B) Partial pressure = total pressure / mole fraction * C) Partial pressure = mole fraction x total pressure * D) Partial pressure = total pressure - mole fraction 9. What is mole fraction? * A) The total number of moles in a mixture * B) the number of moles of a speci c gas divided by the total moles of gas. * C) The total number of moles of just the products * D) the number of moles of just the reactants 10. What are the units of Kp? * A) Always Pa * B) Always atm * C) It has no units * D) It depends on the stoichiometry of the reaction 11. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what is the expression for Kp? * A) Kp = (pNH3) / (pN2)(pH2) * B) Kp = (pNH32) / (pN2)(pH23) * C) Kp = (pN2)(pH23) / (pNH32) * D) Kp = (pN2)(pH2) / (pNH3) 12. A gas mixture contains 0.2 moles of N2, 0.6 moles of H2, and 0.2 moles of NH3. The total pressure is 20 atm. What is the partial pressure of H2? * A) 2 atm * B) 6 atm * C) 12 atm * D) 20 atm fi 13. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), at equilibrium, the partial pressures are: pSO2 = 0.4 atm, pO2 = 0.2 atm, pSO3 = 0.6 atm. What is the value of Kp? * A) 0.15 * B) 6.67 * C) 11.25 * D) 22.5 14. How does increasing the total pressure affect the value of Kp for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g)? * A) increases it * B) Decreases it * C) Doesn't change it * D) Depends on the temperature 15. How does increasing the temperature affect the value of Kp for the *exothermic* reaction N2(g) + 3H2(g) ⇌ 2NH3(g) * A) increases * B) decreases * C) No change * D) depends on the pressure Answers and Explanations: 1. C) The position of equilibrium in terms of concentrations. - Kc uses equilibrium concentrations. 2. A) Kc = ([C]c[D]d) / ([A]a[B]b) - Products over reactants, raised to the power of their stoichiometric coef cients. 3. D) It depends on the stoichiometry of the reaction. - The units vary depending on the powers in the Kc expression. 4. B) The equilibrium lies to the right (products favored). - A large Kc means the concentration of products is much greater than reactants at equilibrium. 5. B) The position of equilibrium in terms of partial pressures. - Kp uses partial pressures of gases. fi  6. A) Kp = (pCcpDd) / (pApBb) - Partial pressures of products over reactants, raised to the power of their stoichiometric coef cients. 7. B) The pressure exerted by an individual gas in a mixture. - This is the de nition of partial pressure. 8. C) Partial pressure = mole fraction x total pressure - This is the correct formula. 9. B) the number of moles of a speci c gas divided by the total moles of gas. Correct de nition 10. D) It depends on the stoichiometry of the reaction correct de nition. 11. B) Kp = (pNH32) / (pN2)(pH23) - Correctly applies the general form to this speci c reaction. 12. C) 12 atm - Mole fraction of H2 = 0.6 / (0.2 + 0.6 + 0.2) = 0.6. Partial pressure = 0.6 x 20 atm = 12 atm. 13. D) 22.5 - Kp = (0.6)2 / (0.4)2(0.2) = 0.36 / 0.032 = 11.25. With correct units, Kp = 11.25 atm-1 14. C) Doesn't change it Kp is ONLY affected by temperature. An increase to the total pressure will shift the position of equilibrium to reduce the moles of gas, but Kp itself will not change. 15. B) decreases For an *exothermic* reaction, increasing the temperature shifts the equilibrium to the left (favoring reactants), thus decreasing Kp. fi fi fi fi fi fi