chem05 - fl(b Write a balanced equation for the overall...

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Unformatted text preview: fl * (b) Write a balanced equation for the overall cell reaction. 5% page 2 (b) In the overall reaction, the number of electrons taken up at the cathode must equal the number released at the anode, and so the first equation must be multi— plied by 2 and the second by 5. Adding the two gives the overall reaction: 2 Mn0;’(aq) + 16 H3O+(qq) + 5 Zn(s) —-—> i ‘ 2 annaq) + 24 H200?) + 5 Zn2+(aq) ' I (0) Calculate the standard cell potential difference, AEO. W (C) The galvanic cell potential is the difference between the standard reduction potential for permanganate (at the cathode) and that for zinc (at the anode): N5" = %°(Mno;an2+) — <~’5"(an“lzn) = 1.49 - (—076) = 2-25 V £2 page 3 Problem #2 (Chemical Kinetics) (worth 20 %) Given the overall reaction, 4HN03 (g) ----- ——> 4N02 + 21120 + oz and the following proposed reaction mechanism for it, (1) HNO3 ——> OH + N02 k1 (2) OH + N02 ——> HNO3 k2 (3) OH + HN03 -—> H20 + N03 kg (4) N03 + N02 ——> N02 + Oz + NO k4 (5) N03 + NO -—> 2N02 k5 with the following intermediates present only in small concentrations, N03, OH, and NO, use the steady—state approximation to derive the differential rate law for this reaction. Show all of your work. N0 : W 3 X3 [WW/0,2] = / 401/02 ji ZSMA90V43] ' ' Mag/damn: - [M03 3 2 Aid/42] x a”, CAI/V423 2 4; [NM 462%] ram] U may) 2. Mi W if” I a we: + éf/Wfl Problem #3 _ (Chemical Kinetics) (worth 25 %) (a) What is the Principle of Microscopic Reversibility (aka, The Principle of Detailed Balancing)? W State it concisely. 7??” Edw‘btifm, g [0,9,2 (b) Consider the balanced chemical equation for overall reaction, 2N02 + F2 ——> 2N02F and its presumed mechanism, II N02 + F2 f NOzF + F ’7 L F + N02 N02F 2/ Using the above Principle, write an expression for the equilibrium constant, K of this reaction in terms of the elementary step rate constants, Show your work in detail. he K; Ova/fl: ' ~ ' Pages [#02]: “aw, J 1,57%; maze = ’Z—/C/V4&F~Ke [FJe m2 I; [we [Ame r A 5/2/42 Fl), mad—92m M 079 3"}; (c) Dun'ng spontaneous radioactive decay of nuclei, what is the order of its kinetics? 3% (d) If the rate constant for radioactive decay is k, what is the expression for the half—life, 1:1/2 ? ‘ r" f 3* (b Z- W xi; / 4219005 I [/2 , 7/ 5/ (6) How should you plot concentration vs. time data for a second order process in order to get a straight line? Show the plot. Label the axes. .: W} ML vs, /1/ y > Car/Q. L/ Problem #4 (Nuclear Chemistry) (worth 15 %) page 6 (a) What condition must nuclei undergoing spontaneous decay (radioactivity ) meet? Explain 3 ii; your answer by combining major results from thermodynamics and from special relativity. : A61<0éwm ‘ AE<0 "Man paw/“9,? ()va W Ma's-Mai MW 4!szm?" fWJ #9; ‘ I")? <0 , - (b) What nuclear process is responsible for the "burning" of stars? A $92. (c) Nuclear Processes: For each of the nuclear reactions given below, name the decay or other process being illustrated in the blank provided. (The symbol, v, refers here to either a neutrino or an anti—neutrino) (1) 161C ————— -—> 15113 + (ic’t + v 20% (ii) fiNa ———————— ——> fiMg+91e + v ’1 £604 2% (iii) 23 +I (316‘ ———————— -—> 2931 a + v 6 Xvi (iv) 2826 u ------------ --> 2814 o + gHe Z) £604 " \ l M m as + an -------- an + + 2 an Wfiwm 4’ 3t”; 3e W; .. M £3\ page 7 Problem #5 (beginning Quantum mechanics) (worth 15 % ) (a) What is the relationship between the wavelength, A, and the frequency, v, of an electromagnetic wave? Write an equation. h c=aw£7i%0 (b) Arrange the following kinds of electromagnetic radiation in order of increasing wavelength, starting on the left of this page with the one having the shortest wavelength and proceeding to the right toward the one with the longest wavelength. You must get all of them correct in order to get credit for this question. e=vh microwaves X—rays , r , ‘ visible light ,_ “:4ng “aw”? ",0, 9, m4 naMW-fig infrared X M74 J M 3 3 3 radio waves . ultraviolet ?) ~————"“‘19 (c) What was the "ultraviolet catastrophe". . x r ‘ m m: a? (d) Particle—Wave Duality: Which experiment that we discus d in class showed the waves can act V— W I722:— 99 +fl- (e) Particle—Wave Duality: Which experiment that we discussed in class showed that particles can flwamwwfifi hydrogen atom) on n, its principal quantum number? Show with an equation. You need not write like particles? Explain the experiment. 7 act like waves? Explain the experiment fianndfiflflféwfl. "WE/rem“? - naxwwwwf%fiw*%Ffl the constants, just the functionality of energy with n. W a; A J. % d" We M . p 59 — wfl f0». 71 W . I) —‘ ‘- ’ pkg“ - m W g m H 0’1 He ATM: fififlfl‘ flwtfiw fififié¢w (f) Bohr Model of the atom: What is the functional dependence of the energy of the Bohr atom (the End of exam. m Hydrogen peroxide, H202, is a possible product of the reduction of oxygen in acidic solution: Problem # 1 (worth 10 % of the grade on this exam) 0; + 2H30+ + 2e- ———— ——> H202 + 21120 E3 = ‘2 It can then be further reduced to water: H202 + 2H30+ + 26 ----- --> 4H20 13% = 1.77 V _________________________.._._____———————————————- (a) Use the half—cell potential just given for the reduction of H202, together with 02 +4H3O+ + 4c“ —————— --> 6H20 E‘1’=1.229V to calculate the standard half-cell potential for the reduction of 02 to H202 in acidic solution. The desired half-cell reaction is obtained by mbtracting the reaction with poten- tial $3 from that with potential The half-cell potentials are not subtracted, how- ever, but combined as described earlier in this section. Taking n] = 4, 727 = 2, and 713 = 2 gives . fl L = M = (4 mol)(1.229 V) - (2 mol)(l.77 V) 2 mol $3 = 0.69 V (b) Write a reduction potential diagram for 02, H202, and H20. The reduction potential diagram is obtained by omitting the electrons, water, and H3O)r from the corresponding half—equations: 0.69 V 1.77 V O) ' H202 1.229 V H20 (c) Is H202 stable with respect to disproportionation in acidic solution? Explain your reasoning. H202 is thermodynamically unstable to disproportionation in acidic solution, because the half-cell potential to its right (1.77 V) is higher than that to its left (0.69 V). The disproportifination of H202 is also spontaneous in neutral solution, but is slow enough that aqueous solutions of hydrogen peroxide can be stored for a long time without deteriorating, as long as they are kept out of the light. Problem # 2 (worth 5 % of the grade on this exam) E Given the following expen'mental data: [A] ' A ~-—> products (b) What is the order of this reaction? _ _ 0) M (c) What are the units of the rate constant? v I (d) What is the integrated rate law? /2 r Ari?“ (e) What is the reaction half—life expression? ‘40 ' __,___——v “p ' kg Problem # 3 (worth 9 % of the grade on this exam) My (a) Consider the (overall) reaction, 2N02 + F2 —-—--> 2N02F with the mechanism, (1) N02 + F2 + N021: + F L . .1 2 NO + F NO P ( ) 2 VT; 2 e overall reaction and the rate Write the relationship between the equilibrium constant, K, for th constants for the elementary steps of the mechanism. This illustrates what principle in ldnetics? Amiga/we = A [flog/Ye C/‘Je i . i ‘ £2 WJCWE a £2 (MK/e 3% a «gr/é MC ; / WEI/it W W) for “unimolecular” decompoSition? Use the steady-state (b) Write the Lindemann mechanism reaction is first order at high pressure and second order at approximation to show that its overall low pressure. Problem # 4 (worth 6 % of the grade on this exam)‘ Complete the following nuclear reactions: 3 3 1 9L _ ---- -— ‘7 (a) 2He+2He >21H+, ZA/e 6 .‘ 1 3 ¢ + ——————— __> + ? 2,45 (c) ngo + %D ------ ~—> £91ch + ? 0’7! E Compare and contrast the following four simple quantum mechanical models; particle in a one dimensional box, rigid rotor, one dimensional harmonic oscillator, and the hydrogen atom. Specifically, (a) sketch at least the first three energy levels for each showing how the spacings between levels change as energy increases, (b) where pertinent, sketch the shape of the potential energy curve for each, (c) label the levels with their quantum numbers, starting with the lowest energy level, ((1) for the first three energy levels in each, sketch the shapes of their wavefunctions, ‘1’, and of ‘1’2, (e) indicate what kind of electromagnetic radaition typically excites transitions between adjacent levels in each model, and (f) indicate what kind of molecular motion is modelled for each. Problem # 5 (worth 20 % of the grade on this exam) Problem # 6 (worth 10 % of the grade on this exam) Briefly define/ describe and explain the significance of each of the following: (a) Stern—Gerlach experiment I j; r M W W M 9mma%Wfl%wmri% (b) Band gap in semiconductors vs. insulators r M970); J M m 'WA (c) Photoelectric effect In. 8.. 157’ = % 7" [Es — {n6 MTM wane fim a” (d) Crystal field theory (e) Ligand field theory . ~ I m - v WW a“ 7' ‘ (f) it back—bonding r r V T 9 7% ‘ ( fit; Mp +5. 7% MW ' ’62 6 . W #a 30 (g) Mulliken electronegativity scale mi W‘ )3; “fif”~a%;+fl> .27 (h) Hamiltonian operator \ , #a/thf—y = (i) Orbital approximation ‘ 'fi%fifif%w -%e W W ‘ F t ‘ 2W NE (a) Predict whether PH3 and SF6 will have dipole moments. Explain your reasoning. Problem # 7 (worth 12 % of the grade on this exam) The NH, molecule has a dipole moment, because the three N—H bond dipoles add to give a net dipole pointing downward from the N atom to the base of the pyramid that defines the NH3 structure. The SF6 molecule has no dipole moment, because each S—F bond dipole is balanced by an equal one pointing in the opposite direction on the other side of the molecule. (b) Predict the structure of IF5 including any bond angle distortions. The structure of IF5. Note the distor— tions of F—I—F bond angles from 90° because of the lone pair at the bottom (not shown). (c) How many normal modes of vibration does IF5 have? 372.; = m—g : /2 (d) Does IF5 have a rotational spectrum? Explain your reasoning. yepJ imam 27— [w A i/‘fble Maw- e (e) Using VSEPR theory and accounting for lone pairs of electrons, predict (and draw) the structure of H20. Show the partial charge distribution that gives water its dipole moment. - ‘ 17’ MAW—P 72M ‘— / 89 76W” ) 4 ,4 70;} M We Mp )7/1 \ ,, H furgfneg’egw 9‘ ’3‘ if (D How many nonnal modes of vibration does water have? Describe them. 3n~6 :r3-3ré ’ 3 71.» $729735?) [3M 0 I074) AW ,4 ieflfl ' Problem # 8 (wonh 14 % of the grade on this exam) [(5/ (a) Draw the molecular orbital correlation diagram for theirnolecular anion, Bi. 02p: I, \\ ‘A ’I/ wt}. 77‘ \l\ \ a I \ I \ I W :5 2,1,: “211’, "is I, \\ 25———@————-(\ I),__®_zs \ l B ®a ' 5 C 2: (b) Write its electronic configuration. 2*23 ‘9296E377 I B‘ d' ti ti ? Wh ? \ (c) s 2 rarnagne corparamagne c y ( m (d) What is the bond order of Bi? '/2 (5 " 2 ) = 3/2 r (e) In principle, B5 is isoelectronic with what neutral diatomic molecule? « BC (0 What is the bond order of B32? MM): 0 K5 Consider the potential energy curves for the neutral diatomic molecule, AB; its cation, AB+; and its anion, AB’, all shown below. This question deals with locating dissociation energies, Do ; equilibrium bond lengths, Re ; ionization energies, 1P ; and electron affinities, EA, on the potential curves shown below. Your answers to (a) and (c) must be drawn on the figure below and must be in terms of these quantities. Problem # 9 (worth 14 % of the grade on this exam) On the diagram above, indicate, like so fine) , answers to the following: figural LC) I (/(a) the [P of AB, the EA of AB, D0 of AB+, D0 of AB', D0 of AB, the energy differences between the three atomic asymptotes as shown (in terms of appropriate IP's or EA's) (b) Write an equation indicating the energetic relationship between D0(AB) and D0(AB'). DOWN MW) = 5,4050% A6437 t/ (0) Indicate the location of Re(AB') on the above diagram. (d) Which of the three is shown as having the greatest bond strength? fig end of exam ...
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chem05 - fl(b Write a balanced equation for the overall...

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