# Wright CHM 1220 - CHM 1220_EquilibriumKineticReview_Fall2017_answers (3 pages)

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## CHM 1220_EquilibriumKineticReview_Fall2017_answers

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- Chm 1220 - General Chemistry II

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CHM 1220 In Class Activity Review of Kinetics and Equilibrium ANSWERS Fall 2017 1 For the phase transition H2O l H2O g at 298 K H 44 0 kJ mol and S 119 J mol K What is the value of G at 298 K when the partial pressure of water is 19 2 torr Relationship for G and partial pressures Gvap G o vap RT ln Q o Gvap Gvap RT ln PH2O Calculate G rxn Q o o o Gvap H vap T S vap PH 2O o Gvap 44 103 J mol 298 K 119 J mol K 1 o Gvap 8 54 103 J mol Plug in vapor pressure and G rxn J J 8 314 298 K ln 0 0253 atm needs to be in atm not torr mol mol K J J J Gvap 8 54 103 9 11 103 5 70 102 0 570 kJ mol mol mol mol Gvap 8 54 103 1 atm 760 torr 2 At 2000 C the value of Kc for the reaction N2 g O2 g 2NO g is 4 10 10 4 What is the value of Kc at 75 C if H 180 6 kJ mol ln K2 H o 1 1 K1 R T2 T1 T1 2000 C 2273 K T2 75 C 348 K N2 g O2 g 180 6 kJ 2NO g K1 4 10 10 4 By lowering the temperature move toward the heat term results in shift of equilibrium to the left and a smaller Kc K2 180 6 103 J 1 1 4 ln K 2 ln 4 10 10 J 8 314 348 K 2273 K mol K ln K 2 52 86 7 80 K2 e 60 7 4 52 10 27 3 Some reactions are so rapid that they are said to be diffusion controlled that is the reactants react as quickly as they can collide An example is the neutralization of H3O by OH which has a second order rate constant of 1 3 1011 M 1s 1 at 25 C If equal volumes of 2 0 M HCl and 2 0 M NaOH are mixed instantaneously how much time is required for 99 999 of the acid to be neutralized Rate law Under initial conditions So Integrated Rate law H3O aq OH aq 2 H2O H O OH rate k H3O OH 3 2 3 0 k 1 3 1011 M 1s 1 0 0 001 remains 1 1 kt 0 00001 H3O 0 H 3O 0 1 1 0 00001 H 3O 0 H 3O 0 99999 t k k H 3O 0 Then 1 1 kt H 3O H 3O 3 0 0 Where H O 0 00001 H O rate k H3O Need time to reach 99 999 consumption Technically since the solutions will be mixed initial concentration of H3O 1 0 M t 99999 7 1 3 10 M 1s 1 1 0 M 7 69 10 s 769 ns 11 CHM 1220 In Class Activity Review of Kinetics and Equilibrium Fall 2017 4 Hydrofluoric acid HF dissociates in water according to the following equilibrium reaction Kc 3 5 10 4 HF aq H aq F aq What is the concentration of H in a 0 0100 M solution of HF H F Kc 3 5 10 4 HF x x Use the quadratic formula to solve for x b b 2 4ac x 2a ax bx c 0 2 x x 3 5 10 4 2 3 5 10 4 4 2 1 4 1 3 5 10 6 0 01 x 3 5 10 4 x 2 3 5 10 6 3 5 10 4 x x 2 3 5 10 4 x 3 5 10 6 0 3 5 10 3 75 10 3 1 71 10 3 M or 1 70 10 3 M 2 H x 1 70 10 3 M 5 The light stimulated conversion of 11 cis retinal to 11 trans retinal is central to the vision process in humans This reaction also occurs more slowly in the absence of light At 80 C in heptane solution the reaction is first order with a rate constant of 1 02 10 5 s 1 a What is the molarity of 11 cis retinal after 6 00 h if its initial concentration is 3 50 10 3 M Rate law Rate k cis retinal First order integrated rate law ln cis retinal kt ln cis retinal 0 ln cis retinal 1 02 10 5 s 1 21 600 s ln 3 50 10 3 M ln cis retinal 5 875 cis retinal 2 81 10 3 M b How much time does it take for 25 of the 11 cis retinal to react Calculate time to reaction to proceed to 25 reacted cis retinal 0 75 cis retinal 0 75 remains First order integrated rate law ln cis retinal kt ln cis retinal 0 ln 0 75 cis retinal 0 kt ln cis retinal 0 ln 0 75 kt t ln 0 75 28 204 s 7 83 h 1 02 10 5 s 1 CHM 1220 In Class Activity Review of Kinetics and Equilibrium Fall 2017 6 Calculate the value of the equilibrium constant Kc for the following reaction 2CH3OH g H2 g C2H6 g 2H2O g from the following information 2CH4 g C2H6 g H2 g CH4 g H2O g CH3OH g H2 g Kc 9 5 10 13 Kc 2 8 10 21 Show your thought process no change K1 2CH4 g C2H6 g H2 g flipped and multiplied by 2 2CH3OH g 2H2 g 2CH4 g 2H2O g add together 2CH3OH g H2 g C2H6 g 2H2O g 1 K2 no change 2 reciprocal and squared 2 1 multiple together K c K1 K 2 2 1 13 K c 9 5 10 1 21 10 29 21 2 8 10 7 The oxidation of iodide ion by hydrogen peroxide in an acidic solution is described by the balanced equation H2O2 aq 3 I aq 2 H aq I3 aq 2 H2O l Initial rate data obtained at 25 C and a constant H are listed in the following table Experiment H2O2 M I M Initial Rate M s 1 0 100 0 100 1 15 10 4 2 0 100 0 200 2 30 10 4 3 0 200 0 100 2 30 10 4 4 0 200 0 200 4 60 10 4 What is the rate law for this reaction at 25 C including the value of the rate constant From Experiments 1 2 H2O2 constant rate doubles I doubles first order with respect to I From Experiments 1 3 I constant rate doubles H2O2 doubles first order with respect to H2O2 Rate law Rate k H 2O2 I Using data from any experiment k Rate 1 15 10 4 M s 1 1 15 10 2 M 1s 1 0 1 M 0 1 M H 2O 2 I

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