Exam 1 of Chemical Kinetics in General Chemistry, Exams of Chemical Kinetics

Download Exam 1 of Chemical Kinetics in General Chemistry and more Exams Chemical Kinetics in PDF only on Docsity! Chemistry 1330H Spring 2021 Professor Keller Personal Performance Assessment #1 KEY Name i ( Student # l.ab Section Multiple Choice (4 points each). Circle the one best answer for each juestion. 1. For a second-order reaction: (A) The rate is proportional to the reciprocal of the rate constant. (B) The half-life is independent of the initial concentration. i { (C) The rate usually decreases with increasing temperature. The rate constant is independent of temperature. (E) None of these statements are true for second-order reactions 2. Which graph would be linear? (A) 1/k versus temperature for any reaction a (B) 1/In [A] versus time for a reaction first-order in A E, versus 1/temperature for any reaction (0) 1/[A] versus time for a reaction second-order in A 3. Which statement is FALSE? (A) In order for most reactions to occur, reactant molecules must collide with ez ch other. (C) According to collision theory, a three-body collision is less likely than a two body collision. (D)In reactions that are second order in one reactant and first order in another, :he slow step generally involves a three-body collision of the reactants. (E) The transition state is a short-lived, high energy state, between reactants anc products. 4. Which statement is true? (A) At a given temperature, all molecules possess the same kinetic ener By. i (B) The activation energy of a reaction depends on the temperature. a (C) First-order reactions are always faster than second-order reactions. ) Unimolecular reactions are always faster than bimolecular reaction: . @ None of the above statements are true. Page 1 of 9 Personal Performance Assessment #1 Professor .<eller Chemistry 1330H Spring 2021 5. The combustion of ethane (C2He) is represented by the equation: 2 C2H6 (g) + 7 O2(g) > 4 COz(g) + 6 H20 (/) In this reaction... (A) the rate of consumption of ethane is seven times faster than the rate of consumption of oxygen. (B) the rate of formation of CO2 equals the rate of formation of water. Y (C) water is formed at a rate equal to two-thirds the rate of formation of CO2 the rate of consumption of oxygen equals the rate of consumption of wat 2r. Oz is formed twice as fast as ethane is consumed. 6. Chlorine, Cl2, reacts with hydrogen sulfide, H2S, in aqueous solution to produce solid sul ‘ur and hydrogen chloride, HCl: Cle (aq) + H2S (aq) -> S (s) + 2 HCl (aq) The rate law for this reaction is found to be: Rate = k{Cl2][H2S]. Which is an accepte ble mechanism of this reaction? uy (A) Ch >clt+cr (slow) Cl + HS > HCl + HS” (fast) Cl +HS > HCl+S (fast) (B)) Ch+HS > HCl+CIt+HS (slow) Cit+HS >HC1+S (fast) (C) Ch > Cl+Cl (fast) Cl+H2S > HCl+HS (fast) HS+Cl > HC1+S (slow) (D) All of these mechanisms are acceptable possibilities. (E) None of these mechanisms are acceptable possibilities 7. The main reason that reaction rates decrease as the temperature is lowered is: (A) Concentration decreases as the temperature is decreased. (B)) The fraction of collisions with energies greater than the activation energ y decreases ¢ as the temperature is lowered. (C) The activation energies increase at lower temperature. (D) The molecules don’t have the correct orientation to react at lower temp: rature. Page } of 9 Personal Performance Assessment #1 Professor Seller Chemistry 1330H Spring 2021 11. (16 points) The isomerization reaction of CH3NC (g) to CHsCN (g) is first-order :n CH3NC, and has a half-life of 12 days at 444 K. (a) Ifa 5.0 L flask is filled with 25.0 g CH3NC and then allowed to react, what mass of CH3CN will be formed in one month (30 days) at 444 K? k- 0.643 0.68 gosre d™' ti), 12a Apis MaSS A Cm anthony 5 Meisen) * 25.0-4.415 = € ——— = 0.58 2S g eg 07 J 3 Meawe * (0.1766 )(255) 2 425 left 3h (b) Draw a picture (Lewis Structure) of the transition | zi aj state in this one-step process. \ ( 7 S \, (c) Why is the reaction so slow? C 2 oi | the trensihon store ( Scoord.. H a , tlhaea wth | cab ) is “y oaaee ee ata bonds to CN. hindered ) vf Hcefoer Aish im 1 Page 5 £9 exay - = locge Ea 3pm Personal Performance Assessment #1 Professor <eller Chemistry 1330H Spring 2021 12. (16 points) Carbon monoxide in converted to carbon and carbon dioxide (this is calliid a “disproportionation reaction”) via the equation below: 2CO(g) > C(s) + COr(g) Protai(Torr) Time (s) 250 0 The reaction is second-order in CO. Starting with only 250 Torr of 237 398 CO, the pressure-time data given in the table were collected, 224 1002 Determine the rate constant for the reaction. (Hint: Torr is just a 211 1801 teeta pase h Far me A C04, Cis) + CO, inihal 250 Tow — 0 Te«r af £34 250-%e = - re D1) - . op ae| an a . (i50-%) Torr me BT ute dit Pao = 250 Tote - a3 Tore) = Ly bdegde E Late) A ( Steer = ae ol oe (348 sec) 4S x10 ee as bee [LP xt Tore Ss CC Page 6 of9 Personal Performance Assessment #1 Professor <eller Chemistry 1330H Spring 2021 13. (16 points) Dinitrogen tetroxide, N2Ou, decomposes to nitrogen dioxide at room temperature in the gas phase: N20, > 2NO2 The reaction is first-order in N2Ou and the activation energy is 54.0 kJ/mol. At 30°, k=5.1x 10 s1. Calculate how much longer, in seconds, it takes for the partii i pressure of N2Os to decrease from 0.10 atm to 0.010 atm at 30 °C compared tc 300°C. 391 ( Be (2 30°C , 303k inf 2 Je “kt GG “(1 ose to kek eal 7 z - (Slo 8 J) es 99 salt S1b x10 Te le FeSO te 4, sft (6, =—T Z00C , me ple Ned Th pw rate constant @ y 000] Sy 0 Tol Cis a3t an Ha [4 ota) Cae 4 nue NC (EFBEN BE) /0. [ ea ky eg = eee -{ A at 300% = 0.{4 5 “P GV. In (22) . -o.a4s" (£) b= (54 13h seconds “ Shs a9 303 = -o,1a4 (4) Page 7: £9 +p