November 2, Possibly Useful Information: 2) ( ) ( ) ( ) ( ) ( ) R = L atm/mol K

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1 Name Student ID # CHEMISTRY 122 [Tyvoll] EXAM II November 2, Possibly Useful Information: 1) ( ) ( ) ( ) ( ) ( ) d (H 2 O) = 1.00 g/ml 2) ( ) ( ) ( ) ( ) ( ) R = L atm/mol K 3) ( ) ( ) ( ) ( ) ( ) N = x c = 3.0 x10 8 m/s 4) ( ) ( ) ( ) ( ) ( ) h = 6.63 x J s 5) ( ) ( ) ( ) ( ) ( ) 1 W = 1 J/s 1 calorie = J 6) ( ) ( ) ( ) ( ) ( ) 1 L = 1000 cm 3 7) ( ) ( ) ( ) ( ) ( ) ln{[a] 0 /[A] t } = kt t 1/2 = 0.693/k 8) ( ) ( ) ( ) ( ) ( ) ln{[a] t /[A] 0 } = kt 9) ( ) ( ) ( ) ( ) ( ) c(h 2 O) = J/g 0 C 10) ( ) ( ) ( ) ( ) ( ) K P = K C (RT) Δn(gas) 11) ( ) ( ) ( ) ( ) ( ) 12) ( ) ( ) ( ) ( ) ( ) 13) ( ) ( ) ( ) ( ) ( ) 14) ( ) ( ) ( ) ( ) ( ) 15) ( ) ( ) ( ) ( ) ( ) Points Missed: Part I Part II Grade (100 Points Possible)

2 Chemistry 122 (Tyvoll) EXAMINATION II November 2, 2007 Name (Please neatly print your name in the space above) Part I. Multiple Choice (3 points each -- Total points = 45) Print your name in the space above and on the answer sheet. Choose the BEST answer for each of the following questions and blacken or mark an "X" in the correct space on the answer sheet. You should use a pencil to mark your answers. Make sure you carefully erase any incorrect answers. Good luck!! 1. Which statement is not correct regarding the function of a catalyst? 1. It lowers the activation energy. 2. It changes the mechanism of a reaction. 3. It affects the rate of a chemical reaction. 4. It raises the energy of the product causing the reaction to be more endothermic. 2. For the reaction, 3 H 2 (g) + CO(g) CH 4 (g) + H 2 O(g), the rate of disappearance of H 2 (g) is the rate of appearance of CH 4 (g). 1. one third 3. three times 2. two times 4. the same as 3. Consider the reaction A 2 B, where the value of K C is Which statement about the system at equilibrium is correct? 1. The amount of A is very close to the amount of B. 2. The amount of A is slightly less than the amount of B. 3. The amount of A is much larger than the amount of B. 4. The amount of A is much less than the amount of B. 5. More information is needed to answer the question. 4. Consider the equilibrium reaction, N 2 (g) + 3 F 2 (g) 2 NF 3 (g) In a particular experiment, the following concentrations are found at equilibrium: [N 2 ] is M, [F 2 ] is M, and [NF 3 ] is M. What is the value of the equilibrium constant?

3 5. Ethyl chloride, CH 3 CH 2 Cl, decomposes according to first-order kinetics when heated as shown below: CH 3 CH 2 Cl (g) C 2 H 4 (g) + HCl (g) If, in an experiment the initial concentration of CH 3 CH 2 Cl (g) was 1.00 x 10-3 M, what was the concentration of CH 3 CH 2 Cl (g) after 3 half-lives had elapsed? x 10-4 M x 10-6 M x 10-4 M x 10-5 M 6. At 1123 K, a dynamic equilibrium exists between carbon monoxide, carbon dioxide and solid carbon: C (s) + CO 2 (g) 2 CO (g) ΔH = kj If K C = 0.153, what is the value of K p for this reaction? 1. K p = K p = 1.66 x K p = K p = K p = 7.09 x For the reaction, 2NO 2 (g)+ F 2 (g) 2 NO 2 F, the rate law is given by: rate = k[no 2 ] 1 [H 2 ] 1 What is the order of this reaction, with respect to H 2 and overall, respectively? 1. 2nd with respect to H 2 and 3rd overall 2. 2nd with respect to H 2 and 2nd overall 3. 1st with respect to H 2 and 3rd overall 4. 1st with respect to H 2 and 2nd overall 8. Which one of the following best describes what occurs in a reaction system when it reaches a state of dynamic equilibrium? 1. all concentrations of reactants and products are the same 2. the sum of the reactant concentrations equals the sum of the product concentrations 3. the number of collisions per unit time is the same for all species present 4. the rates for both forward and reverse reaction processes are the same 9. What is the concentration of OH 1- in a solution that is M Ca(OH) 2, a strong electrolyte? M x 10-2 M M x 10-4 M x 10-3 M 3

4 10. Identify the acids and bases on respective sides of the following equation: HCO OH 1- CO H 2 O 1. acid + base acid + base 4. acid + base base + acid 2. base + acid acid + base 5. acid + acid base + base 3. base + acid base + acid 11. If [OH 1- ] = 5.3 x 10-9 M in an aqueous solution, the solution is best described as 1. acidic 4. alkaline 2. neutral 5. amphoteric 3. basic 12. What is the [OH ] in an aqueous solution of orange juice with [H 3 O + ] = M? M M M 13. The conjugate acid of H 2 PO 4 is 3 1. PO H 2 PO 4 3. H 2 PO 4 4. H 3 PO H 3 PO Which one of the following is the weakest acid? 1. HF 3. HBr 2. HCl 4. HI 15. A ph meter reads What is the [H 3 O + ] in the solution? M M M M M 4

5 Part II - Total points = 55. Answer each of the following questions. SHOW ALL WORK! 1. (11 points) The data in the table below were collected for the solution phase reaction, 2 HgCl 2 (aq) + C 2 O 4 2- (aq) 2 Cl 1- (aq) + 2 CO 2 (aq) + Hg 2 Cl 2 (aq) Experiment [HgCl 2 (aq)], M [C 2 O 4 2- (aq)], M Initial Rate, M s x x x x 10-5 (a) (5 points) Determine and write the complete rate law, including numerical exponents, for this reaction. Be careful! Show your work/thinking for credit! rate = (b) (3 points) Calculate the value of the rate constant, k, including appropriate units! (c) (3 points) Consider the reaction, H 2 (g) + 2 ICl (g) 2 HCl (g) + I 2 (g), where the experimental rate law is first order in H 2 and first order in ICl. Circle any of the following mechanisms that is/are consistent with the observed rate law and briefly show why the mechanism(s) you circled was(were) consistent with the observed rate law. (1) H 2 (g) + 2 ICl (g) 2 HCl (g) + I 2 (g) (elementary process) (2) H 2 (g) + ICl (g) HI (g) + HCl (g) (slow) HI (g) + ICl (g) HCl (g) + I 2 (g) (fast) (3) H 2 (g) + ICl (g) HI (g) + HCl (g) (fast) HI (g) + ICl (g) HCl (g) + I 2 (g) (slow) (4) H 2 (g) + ICl (g) HICl (g) + H (g) (slow) H (g) + ICl (g) HCl (g) + I (g) (fast) HICl (g) HCl (g) + I (g) (fast) I (g) + I (g I 2 (g) (fast) 5

6 2. (9 points) At high temperatures, like those found in internal combustion automobile engines, N 2 reacts with O 2 to produce NO (g), a primary air pollutant. Consider this reaction, at 2300 K where, N 2 (g) + O 2 (g) 2 NO (g) K C = 1.7 x 10-3 If mol NO (g) are placed into a 20.0 L reaction vessel and heated to 2300 K, calculate the equilibrium concentrations of all three species (N 2, O 2 and NO). Show all work, including the appropriate ICE table, for credit! Is this reaction reactant-favored or product-favored at 2300 K? Explain briefly. 6

7 3. (10 points) Although organotin compounds are effective anti-foulants and have saved the shipping industry billions of dollars by reducing fuel consumption and bottom maintenance time, it was found that tributyltin oxide (TBTO) and other related compounds have relatively long half-lives in the environment. Significant concentrations of these compounds are now found in both ocean water and sediments, and they tend to bioconcentrate in marine organisms. As a result, it is common for the concentration of TBTO in marine organisms to be 104 times greater than that in the surrounding water. Recently, levels up to μg/l have been found in waters along the East Coast of the U. S. For TBTO, the estimated rate constant for degradation is k = 2.77 yr -1. (1 year = 365 days) (a) If a quantity of TBTO is released into a shallow bay on May 1, resulting in an initial average concentration of TBTO of 0.50 μg/l in the bay water, what will the concentration of TBTO in the lake water be the next May 1 (exactly one year later)? Assume that the temperature is constant so k doesn t change and that all TBTO remains in the bay. Show all work for credit or partial credit! (b) TBTO interferes with the development of Manila clam embryos. In one waterborne exposure test, embryo development was significantly decreased in a μg/l treatment group. How long will it take for the concentration of TBTO to drop from 0.50 μg/l to μg/l? Show all work for credit or partial credit! (c) What is the half-life (in years and in days) of TBTO? You must show all work for credit or partial credit! 7

8 4. (10 points) Consider the reaction in which 2 NH 3 ( g) N 2 (g) + 3 H 2 (g), where ΔH = kj at 298 K. If N 2 (g), H 2 (g) and NH 3 (g) are initially in equilibrium in a reaction vessel, how will each of the following changes affect the equilibrium concentrations shown below? Assume constant volume except for the last case. Answer the question by writing I (increase), D (decrease) or NC (no change) in each of the blanks provided. Change [NH 3 ] [H 2 ] K C Some H 2 is removed from the container The temperature is increased The pressure of the NH 3 is decreased The volume of the container is increased 5. (10 points) Hydrogen gas can be generated at room temperature (298 K) in a reaction between methane gas and water vapor: CH 4 (g) + H 2 O (g) CO ( g) + 3 H 2 (g), where K C = If the initial concentrations of the gaseous species are [CH 4 ] = M, [H 2 O] = M, [CO] = M and [H 2 ] = M, will more H 2 be formed, will it decompose to make more CH 4 and H 2 O once the mixture achieves equilibrium at 2300 K, or is the system already at equilibrium? Make the appropriate calculations and then clearly discuss your results for credit on this question. 8

9 6. (5 points) The Nobel Prize in Chemistry, one of six Nobel Prizes, is awarded once a year by the Royal Swedish Academy of Sciences in early December. The Nobel Prizes have been awarded annually by the Nobel Foundation in early December since The prize in chemistry is widely regarded as the most prestigious award one can receive in the field of chemical research. Who was the recipient for this year s Nobel Prize in chemistry and what is his/her nationality? What is the recipient s general area of scientific expertise and for what specific achievement was he/she recognized? How does the specific achievement relate to what we have studied this semester? 9