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Exam I Thursday, September 28, 7:00-9:00 pm; rooms are on the website. Conflict: (9/28) 4:30-6:30pm in 101 Transportation Building; sign up in 1026 CA Conflict with conflict? Email me right away. Review sessions: Monday (9/25): 165 Noyes Lab; 7-9 pm Tuesday (9/26): 163 Noyes Lab; 7-9 pm

Exam I Practice exam now posted.. Take when you feel ready for the exam. Take as an actual exam (not just more practice problems). See the front of the exam for information that you are given and the number of problems.

Clicker Question Dinitrogen pentoxide is added to an evacuated rigid container at 25°C. The initial pressure is 1.000 atm. The N2O5 decomposes according to the equation 2N2O5 (g) 4NO2 (g) + O2(g)   At equilibrium the total pressure is determined to be 1.423 atm. Determine Kp for the reaction. a) 2.77 x 10-2 b) 2.93 x 10-2 c) 7.55 x 10-5 d) 0.111 e) 0.141

Clicker Question For which of the following reactions does K = Kp at the same temperature? a) 2H2(g) + O2(g) 2H2O(g) b) 2KClO3(s) 2KCl(s) + 3O2(g) c) CO(g) + H2O(l) CO2(g) + H2(g) d) 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g) e) K = Kp for at least two of the above choices (a-d).

2SO2(g) + O2(g) 2SO3(g) Kp = 1.80 x 10-6 Clicker Question Consider an initial mixture SO2 and O2 in which the partial pressure of SO2 is 3.00 atm and the partial pressure of O2 is 2.00 atm. These gases react according to the following equation:   2SO2(g) + O2(g) 2SO3(g) Kp = 1.80 x 10-6 Determine the partial pressure of SO3 at equilibrium (assume constant volume and temperature). a) 1.64 x 10-3 atm b) 2.85 x 10-3 atm c) 5.69 x 10-3 atm d) 5.40 x 10-6 atm e) I don’t know.

Chapter 6: Challenge Problem

Clicker Question Consider a gas-phase reaction (that is, all species are gases) that has reached equilibrium. To this system we add an inert gas (such as helium) at constant temperature. Which of the following best describes what happens?   a) There is no shift because adding an inert gas does not shift the equilibrium position. b) If the system is at constant volume and K = Kp, then the equilibrium position will shift. c) If the system is at constant volume and K ≠ Kp, then the equilibrium position will shift. d) If the system is at constant pressure and K = Kp, then the equilibrium position will shift. e) If the system is at constant pressure and K ≠ Kp, then the equilibrium position will shift.

Follow Up Question Explain your answer. As part of your explanation provide an example of a chemical equation in which K = Kp, and an example of a chemical equation in which K ≠ Kp and justify your choices. Full credit is reserved for explanations that address all of the conditions given in part a, that use the actual (real) chemical equations, and that correctly incorporate partial pressures (and/or partial concentrations) of reactants and products.

Previous Exam Question Gaseous hydrazine (N2H4) decomposes to nitrogen gas and hydrogen gas. At a certain temperature, Kp = 3.50 x 104 for this reaction balanced in standard form. Pure gaseous hydrazine is placed in an otherwise empty rigid vessel and the pressure is noted. The reaction is allowed to reach equilibrium at this temperature and it is observed that the equilibrium pressure is double its initial value. a. Determine the initial pressure of the hydrazine (in atm). Define any variables. b. What percent (in terms of moles) of hydrazine decomposed to reach equilibrium? Explain your answer. c. Determine the equilibrium pressure of hydrazine (in atm).