6.5 x 10 M/s. t ( ) s

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Caitlin Chandler
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1 1. Iodide ion can be oxidized by iodate ion to triiodide ion: IO3 (aq) + 8 I (aq) + 6 H + (aq) 3 I3 (aq) + 3 H2O(l) a. Using the data from the graph above, estimate the instantaneous rate of formation of I3 at 600 s. Clearly show work on the graph. (4 pts.) [IO 3 ] ( ) M rate t ( ) s mole IO 6.5 x 10 x 3 mole I Ls 1 mole IO x 10 M/s 2.0 x 10 4 M I3 /s b. Initial rate data for the reaction are tabulated below: Exp# [IO3 ]i, M [I ]i, M [H + ]i, M Initial rate, M/s x 10 2x x x 10 2x x x ? 4x 2x 4x Determine the rate law for the reaction (show work on the table). (4 pts.) 1-x [I ] = 4x rate [I ] x [IO3 ] = 2x rate [IO3 ] x [H + ] = 4x rate [H + ] 2 rate = k[io3 ][I ] 2 [H + ] 2

2 c. What is the order of the reaction in H + ion? (3 pts.) 2 nd order d. Calculate the numerical value of the rate constant. Don t forget units. (3 pts.) x 10 M/s k 9.1 x 10 2 M 4 s 1 ( M)( M) ( M) e. Calculate the rate of experiment #5. (4 pts.) rate = 9.1 x 10 2 M 4 s 1 ( M) ( M) 2 (0.0200) 2 = 1.3 x 10 6 M/s f. What function of [I ], when plotted versus time, would give a straight line? What information can be obtained from the slope? (3 pts.) 1/[I ], k g. The rate data of the reaction was collected at different temperatures and functions of the data plotted to determine the activation energy y = (-1.22 x 10 4 )x y = x = 1. Clearly label the x and y axes (above) with the proper function. (2 pts.) lnk (y) versus 1/T (x) 2. Determine Ea of the reaction. (3 pts.) slope = (Ea/R) Ea = ( 1.22 x 10 4 K) x J/mole K = 101 kj/mole

3 Energy 3. Sketch a clearly labeled reaction profile if ΔHreaction = 384 kj. (3 pts.) IO I + 6 H kj 244 kj 3 I H 2 O Reaction Progress 2. Barium peroxide (BaO2) is a powerful oxidizer that can produce Cl2 from Cl : 1) BaO2(l) + 4 HCl(g) BaCl2(s) + 4 H2O(g) + Cl2(g) K = at K a. Calculate the value of K at K, for reaction 2: (4 pts.) 2) 2 BaCl2(s) + 8 H2O(g) + 2 Cl2(g) 2 BaO2(l) + 8 HCl(g) 1 1 K = = = x 10 5 K b. Write the K equilibrium expression for reaction 2. (3 pts.) 8 [HCl] K = [H O] [Cl ] 8 2 c. Calculate the value of Kp for reaction 1 at K. (4 pts.) p Δ n 5 4 K = K RT = x = x 10 3

4 3. A mixture of carbon monoxide and hydrogen is known as synthesis gas and is used to make ammonia and methyl alcohol. Synthesis gas is produced by the reaction of methane with high temperature steam (1100 o C). CH4(g) + H2O(g) CO(g) + 3 H2(g) A mixture of M CH4 and M H2O was heated to 1100 o C. At equilibrium, the concentration of CO was found to be M. Calculate the value of K for the reaction at 1100 o C. (9 pts.) CH4(g) H2O(g) CO(g) 3 H2(g) Initial M M 0 M 0 M x x +x +3x Equilibrium x x x = M 3x [ ] M M M M [CO][H ] ( )(0.0210) [CH ][H O] (0.193)(0.193) K = = = x The environmental carbon cycle depends on many equilibria. One of these is the equilibrium of atmospheric carbon dioxide with water containing calcium ion (from many sources, including limestone, chalk, and old seashells): 3 CO2(g) + 7 H2O(l) + Ca 2+ (aq) CaCO3(s) + 2 HCO3 (aq) + 4 H3O + (aq) H = 8.14 kj Predict the change in amount of carbon dioxide in the air over Lake Erie (increase, decrease, or no change) in response to the following: (5 pts.) a. The lake temperature rises during the summer. increase b. Ammonia fertilizer (a base) leaches into the lake. decrease c. Acid rain falls into the lake. increase d. There is run-off of calcium chloride road de-icer into the lake. decrease e. A high-pressure weather system moves over the lake. decrease

5 5. 2 ClF(g) Cl2(g) + F2(g) K = (at 25.0 C) A flask is filled with M ClF, M Cl2 and M F2. a. Based on a calculation, which direction does the reaction go (to the left or to the right) to reach equilibrium? (4 pts.) [Cl ] [F ] (0.130)(0.130) Q = = = [ClF] (0.500) 2 i 2 i i ; Q > K, reaction goes to left. b. Calculate the molarity of all substances at equilibrium. (8 pts.) [ClF] [Cl2] [F2] initial x x x equilibrium x x x 2 [Cl 2][F 2] (0.130 x)(0.130 x) (0.130 x) K = = = = [ClF] ( x) ( x) (0.130 x) ( x) = ; x = x x = M [ICl] = (0.0106) = M [I2] = = M [Cl2] = = M [Cl 2][F 2] (0.119)(0.119) Check: K = = = matches (rounding) [ClF] (0.521)

6 6. Calculate the ph of the following aqueous solutions. To receive full credit, you must show an appropriate chemical equation for each. Constants in the handout. (30 pts.) a M HC8H8O2 (phenylacetic acid) HC8H8O2(aq) + H2O(l) C8H8O2 (aq) + H3O + (aq) [HC8H8O2] H2O [H3O + ] [C8H8O2 ] initial 0.20 M ~0 0 x +x +x equilibrium 0.20 x x x + [H3O ][C8H8O 2 ] 5 x x K a = = 5.2 x 10 = [HC H O ] 0.20 x x = 3.2 x 10 3 M = [H3O + ]; ph = log(3.2 x 10 3 ) = 2.49 b M NaClO (sodium hypochlorite) NaClO(aq) Na + (aq) + ClO (aq) ClO (aq) + H2O(l) HClO(aq) + OH (aq) [ClO ] H2O [OH ] [HClO] initial 0.10 M ~0 0 x +x +x equilibrium 0.10 x x x [OH ][HClO] K 1.0 x 10 x K = = = = 3.3 x 10 [ClO ] K HClO 3.0 x w 7 b 8 a x = 1.8 x 10 4 M = [OH ]; poh = log(1.8 x 10 4 ) = 3.74; ph = poh = c M HClO3 (chloric acid) HClO3(aq) + H2O(l) H3O + (aq) + ClO3 (aq) [H3O + ] = [HClO3]i = M ph = log(0.0095) = 2.02

7 d M K2O (potassium oxide) K2O(aq) O 2 (aq) + H2O(l) 2 K + (aq) + O 2 (aq) 2 OH (aq) [OH ] = 2 [O 2 ] = 0.10 M; poh = 1.00; ph = poh = e M C2H5NH2 (ethylamine) C2H5NH2(aq) + H2O(l) C2H5NH3 + (aq) + OH (aq) [C2H5NH2] H2O [OH ] [C2H5NH3 + ] initial 0.10 M ~0 0 x +x +x equilibrium 0.10 x x x [OH ][C H NH ] x x [C H NH ] 0.10 x K b = = 6.4 x 10 = x = 8.0 x 10 3 M = [OH ]; poh = log(8.0 x 10 3 ) = 2.10; ph = f M (C5H5NH + )I (pyridinium iodide) (C5H5NH + )I (aq) C5H5NH + (aq) + I (aq) CB of SA so not basic C5H5NH + (aq) + H2O(l) C5H5N(aq) + H3O + (aq) [C5H5NH + ] H2O [H3O + ] [C5H5N] initial 0.15 M ~0 0 x +x +x equilibrium 0.15 x x x [H O ][C H N] K 1.0 x 10 x K = = = = 5.9 x 10 [C H NH ] K C H N 1.7 x w 6 a b 5 5 x = 9.4 x 10 4 M = [H3O + ]; ph = log(9.4 x 10 4 ) = 3.03

2. What mass of an aqueous 22.9% sodium chloride solution contains 99.5 g of water?

2. What mass of an aqueous 22.9% sodium chloride solution contains 99.5 g of water? CHEM 1412 MIDTERM EXAM (100 pts total) ANSWER KEY Student s Name PART A (20 multiple choice questions, 3 pts each): 1. The solubility of a gas in a liquid can always be increased by: a) decreasing the