Chemistry 1212 4 Name______
Chemistry 1212
Exam II
Spring, 2008
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 9 problems on 5 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
1.(15) Consider the reaction:
2 NO (g) + O2 (g) 2 NO2 (g)
Expt # / [NO] / [O2] / Rate (moles/liter·second)1 / 1.66 x 10-6 / 1.66 x 10-6 / 3.32 x 10-8
2 / 4.98 x 10-6 / 1.66 x 10-6 / 2.99 x 10-7
3 / 4.15 x 10-6 / 4.15 x 10-6 / 5.19 x 10-7
4 / 1.05 x 10-5 / 1.22 x 10-5 / ? =
A. Determine the exponents that are part of the rate law expression. Show all work clearly for full credit.
B. Determine the rate constant with proper units. Show all work clearly.
C. Fill in the last entry of the table with a numerical value. No work need be shown but if you want to…
2.(10) Consider the reaction below at a certain temperature. An equilibrium mixture contains 2.0 moles of Fe, 1.0 x 10-3 moles of O2 and 4.0 moles of Fe2O3 in a 2.5 liter container. Calculate the value of Kc for this reaction. Show all work for full credit.
4 Fe(s) + 3 O2 (g) 2 Fe2O3 (s)
3. (15) At a particular temperature, Kc = 3.75 for the reaction shown below. If the initial concentrations of both [SO2] and [NO2] are 0.750 M and the initial concentrations of both [SO3] and [NO] are 1.50 M, calculate the equilibrium concentration of all four gases. Show all work clearly for full credit.
SO2 (g) + NO2 (g) SO3 (g) + NO (g)
4.(10) For the reaction: 2 H2 (g) + 2 NO (g)→ N2 (g) + 2 H2O (g)
A proposed mechanism is:
1. 2 NO N2O2 fast
2. N2O2 + H2 → N2O + H2O slow
3. N2O + H2 → N2 + H2O fast
Very clearly show the expected rate law for the above reaction.
5.(15) A certain reaction has an activation energy of 54.0 kJ/mole. If the temperature is increased from 22 °C to a higher temperature, the rate constant increases by a factor of 7.00. Calculate the higher temperature and show all of your work clearly for full credit.
6.(10) In a study of the reaction shown below at 1200 K, it was observed that when the equilibrium partial pressure of water vapor is 15.0 torr, the total pressure at equilibrium is 36.3 torr. Calculate the value of Kp for this reaction at 1200 K.
3 Fe (s) + 4 H2O (g) Fe2O4 (s) + 4 H2 (g)
7.(5) Hydrogen gas reacts explosively with oxygen gas. However, a mixture of H2 and O2 can exist indefinitely at room temperature. Explain why H2 and O2 do not react under these conditions. Be complete so I am convinced you know.
8.(5) A choice problem. Answer either part A or part B, not both. If both are answered I will only grade part A. No work need be shown or explained, answers only.
A. The activation energy for a reaction: A + B → C + D is 125 kJ/mole and ΔE for the reaction is -216 kJ/mole. What is the activation energy for the reverse reaction:
C + D → A + B?
B. The hypothetical reaction A + 2 B → Products has the rate law: Rate = k[A]2 [B]3. If the reaction is run two separate times, holding the concentration of A constant while doubling the concentration of B from one run to the next, how would the rate of the second run compare to the rate of the first run?
9.(15) Short answers. No work need be shown, credit is for correct answer only.
An important reaction in the commercial production of hydrogen is:
CO (g) + H2O (g) H2 (g) + CO2 (g) ΔH = negative
How will this system at equilibrium shift in each of the five following cases?
A. Gaseous carbon dioxide is removed. ______
B. Water vapor is added. ______
C. Pressure is increased by adding Helium gas. ______
D. The temperature in increased. ______
E. The volume of the container is decreased. ______
Bonus: Which of the above conditions increases the K value? ______
(Only one correct answer is needed)