EXAM PRACTICE QUESTIONS Chapter 17 1. Write the equilibrium constant expression for the following reaction. Answer: Kc = [NO]4[H2O]6[NH3]4[O2]5 2. Some nitrogen and hydrogen gases are pumped into an empty 5.00-L vessel at 500 qC. When equilibrium was established, 3.00 moles of N2, 2.10 moles of H2, and 0.298 moles of NH3 were present. Evaluate Kc at 500 qC. Answer: Kc = 0.080 3. The equilibrium constant, Kc, for the following reaction is 0.0154 at a high temperature. A mixture in a container at this temperature has the concentrations: [H2] = 1.11 M, [I2] = 1.30 M and [HI] = 0.181 M. Will more product or more reactant be formed, or is the reaction at equilibrium? Answer: Q = 0.227 > Kc, shifts left, reactants are produced 4. Kc = 0.040 for the system below at 450 qC. If a reaction is initiated with 0.20 mole of Cl2, and 0.20 mole of PCl3 in a 1.0-L container, what concentration of PCl5 will be present at equilibrium? Answer: 0.13 M 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g)3 H2(g) + N2(g) 2 NH3(g)H2(g) + I2(g) 2 HI(g)PCl5(g) PCl3(g) + Cl2(g)5. Consider the equilibrium system below. Predict the affect on the equilibrium due to the application of each of the following stresses. A) adding Cl2 ______________ B) lower the temperature ______________ C) decreasing volume at constant temperature ______________ D) decreasing O2 ______________ Answer: right, left, left, right 6. A system at equilibrium in a 1.0-L container was found to contain 0.20 mol of A, 0.20 mol B, 0.40 mol C, and 0.40 mol of D. If 0.15 mol of A and 0.15 mold of B are added to this system, what will be the new equilibrium concentration of A? Answer: 0.25 M 7. Consider the equilibrium system below. At 250. qC a sample of PCl5 was placed in a 24-L evacuated reaction vessel and allowed to come to equilibrium. Analysis showed that at equilibrium 0.42 mole of PCl5, 0.64 mole of PCl3, and 0.64 mole of Cl2 were present in the vessel. Calculate Kp for the reaction at 250. qC. Answer: 1.8 2 Cl2(g) + 2 H2O(g) + heat 4 HCl(g) + O2(g)A(g) + B(g) C(g) + D(g)PCl5(g) PCl3(g) + Cl2(g)8. A sample of only solid ammonium chloride was heated in a 1.00-L container at 500. qC. At equilibrium, the pressure of NH3(g) was found to be 1.75 atm. What is the equilibrium constant, Kc, for the decomposition at this temperature. Answer: 7.62 u 10-4 9. Consider the following reaction at 25 qC for which 'Hq is -26.9 kJ and 'Sq is 11.4 J/K. Evaluate the equilibrium constant, Kp, for the reaction at 25 qC. R = 8.314 J/molK. Answer: 2.05 u 105 10. The following picture represents a mixture that contains A atoms, B atoms, and AB and B2 molecules for the hypothetical reaction given below. Calculate the equilibrium constant, Kc, for the reaction. Answer: 1 NH4Cl(g) NH3(g) + HCl(g)Cl2(g) + I2(g) 2