Chem 4A - Fall 2006 - Head-Gordon - Midterm 1

Chem 4A - Fall 2006 - Head-Gordon - Midterm 1 - Chemv 4A,...

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Unformatted text preview: Chemv 4A, Fall 2006 Midterm Exam 1, September 22, 2006. Prof. Head-Gordon, Prof. Moretto Name: K E TA: Grade: 1. (5 points) 2. (6 points) 3. (8 points) 4. (5 points) Total: Closed book exam. There are 6 pages. Calculators are OK. Set brains in high gear and go! Use back side of pages for scribble paper Some possibly useful facts and figures: R = 8.3145 J mol'1 K'1 molar volume at STP = 22.4 L h=6.6261x10'34Js h=h/27z: c = 2.9979 x 108 m s"1 m. = 9.1094 ><10'31 kg N0 = 6.0221 x 1023 mol‘1 Some possibly relevant eguations: Planck relation: E = hv de Broglie relation: 1) = h / A. wave equation: 0 = VA uncertainty principle Apr 2 h / 2 2 2 2 particle-in-a-box En = n 7‘ 7: ‘Pn = Jim—’33 2ma a a Zz hydrogen atom E, = ———2Rw Rm = 2.18 x 10"8J n linear momentum p = mv kinetic energy T = %mv 1. Nitryl chloride, NOZCl, is known to decompose to N02 and C12. (a) (2 points) Write Lewis structures for NOZCl, given that the chlorine (7 valence electrons, atomic number Z=17, relative atomic mass M=35.453) atom and both oxygen (Z=8, M=15.999) atoms are bonded to the nitrogen (Z=7, M=14.007). Be sure to show the role of resonance structures if there is more than one plausible Lewis structure. Also show any formal charges. C9 _. no " \ Q“) \ a; « N ’— CL <—$ \N ~—— CIA Odds (I) . // 6. / n P IO,— I FflSGVxOmrch (b) (1 point) Write a balanced equation for the decomposition of nitryl chloride. 2Nozct ~—> zixsolé-gactlca3 (.3) (c) (2 points) If 2.00g of nitryl chloride decomposes to yield N02 and C12, calculate the volume of gaseous products under standard conditions. 2. (a) (2 points) The work function of metallic sodium is 4.4x10"9 J. What is the longest wavelength of light that could be expected to cause electron emission from sodium? W 4") Omani Wm ‘ it“; : Mao”? >WW)! 4 (44:53" >< 2‘9 792m? ~ 25x 1 A l “H tttttt “2.. ' 4°SXIO m M 4-4vio“9 (b) (2 points) Suppose electrons have been accelerated to a kinetic energy of 1x106 J/mol. What is their effective de Broglie wavelength? E= Wm => P= J2me = 2x94xto'3‘xtxlo‘ 60,4013 Le- P: 131x162" kg m s‘.‘ <1) - x —34 -10 l; k/F : élé’xig’l‘r : 38H“) m (3) (c) (2 points) Estimate the de Broglie wavelength of a spilled pea as it hits the floor. Show your assumptions clearly. heal/Qt Ni m 3 mass ~ mlOggkg FM ‘79 (I) ._l SpaLCQ’V i MS 7— N k M S-‘ P 9 - . in [0'33 —3o MJLW 3 =7 13—» 7 ~10 m Wat/«Wank 3. Suppose an electron is known to be within a 2 A distance (something like a chemical bond). (a) (1 point) What is the minimum uncertainty in its momentum? f’ ‘ APA" 2 V473 ' Li ~34 A >/ L ___ lqo ‘— 2’6X10—25 k mg] <1 F 4WA2L AFlele 3, (b) (3 points) Calculate the wavelength of light necessary to excite this electron from its ground state to its first excited state, assuming that these states can be described as the lowest and next to lowest energy levels of the particle in a box. E : i1: Whirl n1 _, him; 0 a. n 4" 2M 1’ L 2 0L 0“ 8M0» flzl m m 5401‘?“ n=2 m m 13* Ma'an stain 2. ‘34 )- AREEEF L144) _(ééZélo “:3 AOL gm; Xx 9 lO9¥lD >< (2‘40 > function and the probability density associated ticle in a box. ,L ( 1 mix ) (c) (2 points) Make a sketch of the wave with the ground state and the first excited state of the par U 0L WWW my (d) (1 point) How many nodes does the state of the particle in a box with quantum number (MW (e) (1 point) Give a reason why the energ on classical waves) ‘ 514W 1Vme fl “lbw [AWQ/xfl le’C W-l-oou— 9 bfli P:h/?\ N howdy/6V “6W . a 5-. int/2 N Wm? LW QWQL n have? y increases with the number of nodes (not based Waawihafiva SWDAZ>WP .1)an owl/«3?; 5 4. Atomic energy levels (a) (1 point) Ionization is the process of removing an electron from an atom or a molecule. Does this process give off energy or require energy? Explain your answer carefully. I '1 W61LCJYMQW~O 0/1‘ W * Lame “he; sic/W (A C “I M. Ema?) a «40mer to woo at to Marmot, (b) (1 point) Evaluate the energy change associated with removing the electron from He“. AE = Em — East M) 2. 1X _ x A I all) 1 i O __ 2 E90 ., 2 11% to ; quqbigj (9.; u n" l ({Pcznlévnm/Z‘ (c) (1 point) Would you expect the ionization energy of the first electron from He to be W0"? . larger or smaller than the answer you obtained in (b)? Explain carefully. an A 5 77; , Ag; -E<h=l Ll-e :_ (fried) 2937 QX/whx/b is elachmfi'ng muéasywflfiu '1th Z=2~Q {48—min Sad/lefi- W15 [/3 3W. (d) (2 points) The ionization energy of the potassium atom (K: Z=19; l valence electron) is about one third smaller than the ionization energy of a calcium atom (Ca: Z=20; 2 valence electrons). However the ionization energy of K+ is nearly 3 times as large as Ca+. Can you explain these results? W a Zcff (35 > Zen”) (3: K> W K in»? chv'l Quit Ca has 1< Zgfl<2 _ t 9 ~ « ~ awn: a K V 7 f —-r 4—‘W ~______ _ /. _ "wwfl — F C ) ...
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This note was uploaded on 04/20/2008 for the course CHEM 4a taught by Professor Gordon during the Fall '06 term at University of California, Berkeley.

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Chem 4A - Fall 2006 - Head-Gordon - Midterm 1 - Chemv 4A,...

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