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Unformatted text preview: Your name (Last) (First) Your section Your TA Student ID Signature Midterm 11 6% Friday Feb. 22, 2008 Ta 2:10 PM — 3:00 PM CHEM 2A, Section C, Winter 2008 Professor Guo This is a closed book exam. The only thing you may consult with is a pocket calculator or similarly functional math tool. There are 7 pages and a periodic table on the back; please make sure your exam is complete before starting. Section points Ui-DUJN—t Total _J_ /120 _| Problem 1 (40 points) 1 mole of hydrogen gas (H2) and 1 mole of oxygen gas (02) are stored in a 50 liter container at room temperature. What is the ratio of the speed of H2 to 02? (6 points) - 1E. 1’ 1—} Following the question above, which gas occupies a larger volume? Which gas exerts greater pressure against the container? (6 points) gall/“Q I What are phOtonS? And if electrons carry no charge, can photons still be able to excite them? (6 points) { EM waves and Path 25 [\l O After solving the Schrodinger equation for hydrogen atoms, you will get the energies and wavefunctions. Name three different such wavefunctions with different principal and angular momentum quantum numbers. (9 points) is 2? 367i Why is human beings not considered as waves in the quantum mechanics sense? (5 points) . h +12 0 In em Vt} )x ‘7‘ ’57 What is the wavelength for the wave with the longest wavelength for an electron in a box (width of the box is L), and what is the energy of the system when the electron is at this level? (8 points) N121. EU: T?- L1 (n:\> Xrn Problem 2 (20 points) A thermal decomposition reaction occurs to NaN3 (sodium azide) to produce nitrogen gas and sodium metal, a chemical reaction used in airbags in automobiles. 100 g of NaN3 is used to produce nitrogen gas in an enclosed chamber at 100 °C. Balance the reaction, and calculate the amount N2 gas produced in this decomposition reaction if all NaN3 is decomposed. (10 points) chNgcle—‘fi \\\QC 3 {i 7' l (“0‘ .8 "gmo‘ “MCJ Hakka Z‘BC‘ mz‘t / \“o\ 2.8 . 1,30» a:er (044,0) mo “ If the reaction occurs in a helium background gas (there will be no reactions between helium and any other chemicals in the chamber), and the pressure of helium is 5 atm and the size of the chamber is 50 liters, calculate the partial pressure of nitrogen gas in the chamber. What is the total pressure of the gases in the chamber? (10 points) O . 082 com x ((04,: )4/ 63 ,97ml. __—~ 1:) '2: ":lul ah“ Problem 3 (20 points) Due to the incomplete shielding of the ten electrons in 1322s22p6 in sodium on the eleven nuclear charges, the effective nuclear charge experienced by the most outside 3s1 electron is approximately 2.20 instead of 1. Use your own words to define effective nuclear charge (5 point) ‘il/xr, Poéii’m/C Lid/«’9 ‘ +141 ghechon upilerccpgpcwmkfix ‘ flit-{MA y Using the table given below, provide a brief calculation analysis that shows the effective nuclear charge is 2.2 and not 1.0. (10 points) Screening With Remaining Electrons in Electrons in factor electrons electrons in n-l shell <n-1 shells in outer the same shells shell (same 11) For 1s electrons None 0.3 | N/A N/A Fro ns and np None 0.35 0.85 1 electrons For nd and nf None 0.35 1 1 electrons 11-» 00H xgxoss : Ilr2.-c.?: 2‘2. Predict the ionization energy of the valence electron based on the effective nuclear charge given above. (5 points) Problem 4 (20 points) Using the table given below, calculate the effective charge for an extra electron in hydrogen and helium. Which of these two extra electrons is more stable? (10 points) Screening With Remaining Electrons in Electrons in ’ factor electrons electrons in n-l shell <n-1 shells in outer the same shells shell (same n) For 1s electrons None | 0.3 l N/A JEN/A fFro ns and np None 0.35 0.85 1 electrons For nd and nf j None 0.35 1 1 electrons I ~- __ 2— 13 6+ H > H Ku‘gt’a H: ":ZFQR: l—O.3S=O.6S 5‘: ’ 2. A He \ 1‘51 (H—JRQ-r‘r IS ZS 5 Qua; Z——o.85x'2 = 0,5 En=~—-——-- .. r2“ :- 56:- ‘4’l'v2. EX’W‘EIR He Ts less SE‘ELL a 2“; Compare the sizes of following pairs: (1) sodium and magnesium atoms, (2) Na+ and Na', and (3) Br' and Rb+. (10 points) Problem 5 (20 points) 55 (please write it out explicitly) to fill the electron shells of Na, Using the Aufbau proce Ge, and Ti, starting from 1s and include all the valence shells. (10 points) _ "L z , \ ,, [\lc‘ : I S 1 S 1 3 S ‘ . r z Mb / / (:6 T7 1 151’ 2 51113 " (5L 2 slip" ‘33 3? 7.x 2 to J /_ fl '36 5P wage as ? )4 . ' é: y w «J Assign quantum numbers to all the electrons in the valence shell(s) for Ge. (10 points) ‘7. / * W155j2 ...
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