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MT1 Prep

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1 1 1. If the equilibrium constant for the reaction A + 2B C + 5/2 D has a value of 4.0, what is the value of the equilibrium constant for the reaction 2C + 5D 2A + 4B at the same temperature? (a) 0.25 (b) 0.063 (c) 2.0 (d) 8.0 (e) 16 2. At 445oC, Kc for the following reaction is 0.020. 2HI(g) H2(g) + I2(g) A mixture of H2, I2, and HI in a vessel at 445oC has the following concentrations: [HI] = 2.0 M, [H2] = 0.50 M and [I2] = 0.10 M. Which one of the following statements concerning the reaction quotient, Qc, is TRUE for the above system? (a) Qc = Kc; the system is at equilibrium. (b) Qc is less than Kc; more H2 and I2 will be produced. (c) Qc is less than Kc; more HI will be produced. (d) Qc is greater than Kc; more H2 and I2 will be produced. (e) Qc is greater than Kc; more HI will be produced. 3 Nitrosyl chloride, NOCl, dissociates on heating as shown below. When a 1.50 gram sample of pure NOCl is heated at 350oC in a volume of 1.00 liter, the percent dissociation is found to be 57.2%. Calculate Kc for the reaction as written. NOCl(g) NO(g) + 1/2 Cl2(g) (a) 0.876 (b) 9.26 (c) 0.107 (d) 1.75 x 10-4 (e) 0.0421 4. Consider the reaction: N2(g) + O2(g) 2NO(g) Kc = 0.10 at 2000oC Starting with initial concentrations of 0.040 mol/L of N2 and 0.040 mol/L of O2, calculate the equilibrium concentration of NO in mol/L (a) 0.0055 mol/L (b) 0.0096 mol/L (c) 0.011 mol/L (d) 0.080 mol/L (e) 0.10 mol/L2 2 5. Kc = 0.040 for the system below at 450oC. If a reaction is initiated with 0.40 mole of Cl2 and 0.40 mole of PCl3 in a 2.0 liter container, what is the equilibrium concentration of Cl2 in the same system? PCl5(g) PCl3(g) + Cl2(g) (a) 0.07 M (b) 0.16 M (c) 0.11 M (d) 0.04 M (e) 0.26 M 6. The reversible reaction: 2SO2(g) + O2(g) 2SO3(g) has come to equilibrium in a vessel of specific volume at a given temperature. Before the reaction began, the concentrations of the reactants were 0.060 mol/L of SO2 and 0.050 mol/L of O2. After equilibrium is reached, the concentration of SO3 is 0.040 mol/L. What is the equilibrium concentration of O2? (a) 0.010 M (b) 0.020 M (c) 0.030 M (d) 0.040 M (e) none of these 7. Consider the gas-phase equilibrium system represented by the equation: 2H2O(g) 2H2(g) + O2(g) Given that the forward reaction (the conversion of "left-hand" species to "right-hand" species) is endothermic, which of the following changes will decrease the equilibrium amount of H2O? (a) adding more oxygen (b) adding a solid phase calalyst (c) decreasing the volume of the container (the total pressure increases) (d) increasing the temperature at constant pressure (e) adding He gas 8. Consider the equilibrium system: 2ICl(s) I2(s) + Cl2(g) Which of the following changes will increase the total amount of of Cl2 that can be produced? (a) removing some of the I2(s) (b) adding more ICl(s) (c) removing the Cl2 as it is formed (d) decreasing the volume of the container (e) all of the above3 3 9. At equilibrium, a 1.0 liter container was found to contain 0.20 moles of A, 0.20 moles of B, 0.40 moles of C and 0.40 mole of D. If 0.10 moles of A and 0.10 moles of B are added to this system, what will be the new equilibrium concentration of A? A(g) + B(g) C(g) + D(g) (a) 0.37 mol/L (b) 0.47 mol/L (c) 0.87 mol/L (d) 0.23 mol/L (e) 0.15 mol/L 10. Consider the following system in a 1.00 L container: A(g) + B(g) 2C(g) The equilibrium concentrations at 200oC were determined to be: [A] = 0.200 M [B] = 3.00 M [C] = 0.500 M How many moles of A must be added to increase the concentration of C to 0.700 M at 200oC? (a) 0.225 mol (b) 0.305 mol (c) 0.417 mol (d) 0.610 mol (e) 0.700 mol 12. Kc = 0.040 for the system below at 450oC: PCl5(g) PCl3(g) + Cl2(g) Evaluate Kp for the reaction at 450oC. (a) 0.40 (b) 0.64 (c) 2.4 (d) 0.052 (e) 6.7 x 10-4 13. For a specific reaction, which of the following statements can be made about K, the equilibrium constant? (a) It always remains the same at different reaction conditions. (b) It increases if the concentration of one of the products is increased. (c) It increases if the concentration of one of the reactants is increased. (d) It may be changed by the addition of a catalyst. 14. Which salt is not derived from a strong acid and a strong soluble base? (a) MgCl2 (b) Ba(NO3)2 c) LiClO4 (d) CsBr4 4 (e) NaI 15. In a sample of pure water, only one of the following statements is always true at all conditions of temperature and pressure. Which one is always true? (a) [H3O+] = 1.0 x 10-7 M (b) [OH-] = 1.0 x 10-7 M (c) pH = 7.0 (d) pOH = 7.0 (e) [H3O+] = [OH-] 16. If Kw is 2.9 x 10-15 at 10oC, what is the pH of pure water at 10oC? (a) 6.72 (b) 7.00 (c) 7.27 (d) 7.53 (e) none of these 17. The pH of a solution is 4.80. What is the concentration of hydroxide ions in this solution? (a) 4.2 x 10-9 M (b) 1.6 x 10-5 M (c) 3.6 x 10-12 M (d) 6.3 x 10-10 M (e) 2.0 x 10-8 M 18. A solution in which [H+] = 10-8 M has a pH of ___ and is ___. (a) 8, acidic (b) 6, basic (c) -6, basic (d) -8, neutral (e) 8, basic 19. The pH of a 0.02 M solution of an unknown weak acid is 3.7. What is the pKa of this acid? (a) 5.7 (b) 4.9 (c) 3.2 (d) 2.8 (e) 3.7 20. Which of the following solutions has the lowest pH at 25oC? (a) 0.2 M sodium hydroxide (b) 0.2 M hypochlorous acid (c) 0.2 M ammonia (d) 0.2 M benzoic acid5 5 (e) pure water 21. A 0.10 M solution of a weak acid, HX, is 0.059% ionized. Evaluate Ka for the acid. (a) 3.8 x 10-9 (b) 6.5 x 10-7 (c) 7.0 x 10-6 (d) 4.2 x 10-6 (e) 3.5 x 10-8 22. What is the percent ionization of a 1.2 M HF solution? Ka HF =6.8x10-4 (a) 2.4 % (b) 4.2 % (c) 0.84 % (d) 0.082 % (e) 0.22 % 23. Which of the following is true about a 0.10 M solution of a weak acid, HX? (a) [X-] = 0.10 M (b) pH = 1 (c) [HX] > [H+] (d) [H+] = 0.10 M (e) both b and d 24. Calculate the hydrolysis constant for the cyanide ion, CN-. Ka HCN=4.9x10-10 (a) 2.5 x 10-5 (b) 1.0 x 10-7 (c) 4.0 x 10-10 (d) 5.6 x 10-10 (e) none of these 25. What is the concentration of a sodium acetate solution if the pH of the solution is 9.19? Ka acetic acid =1.8x10-5 …


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