All Notes, Books, Etc., Must Be Placed out of Sight. Please Read Each of the Problems Carefully s1

Chemistry 1212 Exam II Summer, 2002

Name______

All notes, books, etc., must be placed out of sight. Please read each of the problems carefully. If something is not clear, please ask.

The exam consists of 8 problems on 4 pages, and a Take-Home extra credit on the fifth page. Make sure your exam is complete. The exam is worth 100 points with each of the problems labeled as to its point value.

Answers should be placed in the space provided and written legibly. If I cannot read it -- it is wrong. You MUST show your work clearly for each problem in order to receive full credit. Please include an explanation whenever asked to or whenever necessary to make your answer clear. If I cannot understand it -- it is wrong. Please put your name on every page of the exam.

There are scratch papers and periodic tables available for your use. If you require more data, please ask.

As usual, no cheating is allowed. Good Luck!

DATA 760 mm = 760 torr = 1 atm

( l i t e r a t m ) J o u l e R = 0 . 0 8 2 1 = 8 . 3 1 ( m o l e K ) ( m o l e K ) Chemistry 1212 2 Name______

1.(15) The initial rates listed in the table were determined for the reaction: 2 NO(g) + Cl2 (g) → 2 NOCl(g)

Experiment [NO] [Cl2] Initial rate of consumption of Cl2 (mole/litersec) 1 0.13 0.20 1.0 x 10-2 2 0.26 0.20 4.0 x 10-2 3 0.13 0.10 5.0 x 10-3 Determine the complete rate equation complete with exponents and a numerical value for the rate constant with proper units. Show all work clearly or include an explanation in order to receive full credit.

2.(15) At a certain temperature the reaction below has an equilibrium constant, -2 Kc = 5.8 x 10 . Calculate the equilibrium concentrations of PCl5, PCl3, and Cl2 if the initial concentrations are [PCl5] = 0.200 M, [PCl3] = 0.100 M, and [Cl2] = 0.040 M. Show all work clearly for full credit.

PCl5 (g)  PCl3 (g) + Cl2 (g)

3. (10) Consider the following mechanism for the reaction of nitric oxide and hydrogen: Chemistry 1212 3 Name______

k1 (1) 2 NO(g) N2O2 (g) (Fast) k-1

k2 (2) N2O2 (g) + H2 (g) N2O(g) + H2O(g) (Slow)

k3 (3) N2O(g) + H2 (g) N2 (g) + H2O(g) (Fast)

Write the predicted rate law from this mechanism. Remember that the rate expression can only contain terms in the overall chemical reaction. Be clear in your presentation of your work.

4.(10) The oxidation of Br¯ by BrO3¯ in acidic solution is described by the equation:

+ 5 Br¯ (aq) + BrO3¯ (aq) + 6 H (aq) 3 Br2 (aq) + 3 H2O(l)

The reaction is found to be first order in [Br¯], first order in [BrO3¯], and second order in [H+]. a. What is the change in reaction rate change if the [H+] is tripled? ______b. What is the change in reaction rate if [Br¯] and [BrO3¯] are both cut in half? ______

+ c. What is the change in reaction rate if [Br¯] and [BrO3¯] are both doubled and [H ] is cut

in half? ______

No work needs to be shown for problem #7, answers only will count.

5.(15) The equilibrium constant, Kp, for the reaction: PCl5 (g)  PCl3 (g) + Cl2 (g) is 3.81 x 102 at 600 K and 2.69 x 103 at 700 K. Answer the following: Chemistry 1212 4 Name______

a. How does [PCl5]eq change if the volume is increased? ______b) What direction does the equilibrium shift if 1 atm of Ar(g) is added? ______c) How does [Cl2]eq change if we add a catalyst? ______d) Is the reaction as written endothermic or exothermic? ______e) How does Kp change if we inject more PCl3 (g) into the equilibrium system? ______

24 6.(10) At 25C, Kc = 1.6 x 10 for the reaction shown below. Calculate the concentration of

[CO2] gas that is in equilibrium with solid CaO and solid CaCO3 at 25C. Show work or include an explanation so I know that you know what you are doing.

CaO(s) + CO2 (g)  CaCO3 (s)

7.(10) Values of Ea = 183 kJ/mole and E = 9 kJ/mole have been measured for the reaction: 2 HI(g) → H2 (g) + I2 (g)

Sketch a reaction coordinate diagram for this reaction that has clearly labeled axes and also clearly indicate the positions of Ea and ΔE. Chemistry 1212 5 Name______

8.(15) At 700 K, Kp = 0.140 for the reaction shown below. Calculate the equilibriuim partial pressures of ClF3, ClF, and F2 if only ClF3 is present initially at a partial pressure of 1.47 atm. Show all work clearly for full credit.

ClF3 (g)  ClF(g) + F2 (g)