1. As always… Lon-Capa assignments Lecture videos Textbook Read
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2. 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? me right away.
Review sessions:
Tonight: 165 Noyes Lab; 7-9 pm
Tuesday (9/26): 163 Noyes Lab; 7-9 pm

3. Exam I Practice exam is online. 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.

4. Reaction Quotient (Q)

5. Chapter 6: #18
There is only one value of the equilibrium constant for a particular system at a particular temperature, but there are an infinite number of equilibrium positions. Explain.

6. K is a Constant (at given T)

7. Clicker Question
Consider the “pop” bottles at the beginning of lecture in which we react hydrogen gas and oxygen gas to produce water. Which of the following correctly describes what would happen if we carried out the reaction at a higher temperature?
a) Equilibrium would be shifted to the right and the value of K would increase.
b) Equilibrium would be shifted to the right and the value of K would decrease.
c) Equilibrium would be shifted to the left and the value of K would decrease.
d) Equilibrium would be shifted to the left and the value of K would increase.
e) Equilibrium would be shifted but the value of K would remain constant.

8. Chapter 6: Challenge Problem

9. 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.

10. 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.

11. Chapter 6: Challenge Problem

12. 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).

13. Chapter 6: Challenge Problem

14. Clicker Question
How many of the following is/are true about a system at equilibrium?
I. The concentration(s) of the reactant(s) is equal to the concentration(s) of the product(s).
II. The concentration of reactant(s) is constant over time.
III. No new product molecules are formed.
IV. The rate of the reverse reaction is equal to the rate of the forward reaction and both rates are equal to zero.
a) 0 b) c) d) e) 4

15. Clicker Question
For a certain reaction at 25.0C, the value of K is 1.2  10–3. At 50.0C the value of K is 3.4  10–1.
This means that the reaction is
a) exothermic.
b) endothermic.
c) Impossible -- K cannot change
d) More information is needed.
e) I do not know.