Midterm 1 - Name ID First Midterm Chem 20A Fall 2008 Read...

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Unformatted text preview: Name ID First Midterm - Chem 20A Fall 2008 Read all three questions before answering. They are NOT ordered by difficulty. Use only pencils and calculators; anything else (books, notes, etc.) are not allowed. Don’t spend unnecessary time on mathematical manipulations. Useful info: h : 6-10'341 s v : V / X c = 300,000 km/sec me: 9.1-10‘3‘kg 1eV= 1.6 ~10‘19J 1 mol 2 6-1023 ”hp : h p=mv density(one-e1ectron—in-orbital-‘P—at —position _ r ) = |‘I’(r)|2 E(kinetic) = % mv2 E(total, Hydrogen-like-atom) = —zz 13.6eV / n2 hzn2 E(total, 1-D article in abox = p ) 8mL2 1) Say we conduct a photoelectric—effect experiment with light of a given frequency, and find, that for that frequency, we can stop the electron flow by applying on the sample a reserve voltage of at least 1.25V. Assuming we do not apply the reserve voltage then, for that given frequency: a) What’s the maximum velocity of the emitted photoelectrons 1.25 V A IZSCV CEway cad. e/Eclwn {5215) K. E : /-25e,V f M) :2 Gan/”J— /~ cV ' Kg; :1 Me \fz : 2.0mm” U— 2 v - W 9‘ I ”/0'3'19 V: {(3,000 {$2. —; C63X/0’c‘? M b) What’s the mini mum Awavelength of these electrons? I? : {A70 0:5 2:}? .— ev (7.1% 315)(4;3x/o‘g4) 2: 7.7 9 wow/n *‘ 9.97/4/ 7-) a) Let’s assume that the 18 orbital has the following mathematical form (This is not the correct form, but it is close enough for our purposes here). ‘I’ls (x,y,z) : 0.91 A” 1+4(r/X)2 where r is the spherical coordinate which is the distance from the origin (r = sqrt(x2+y2+zz)). Calculate the probabigty to find Electrons in He in the box 2 —1 .1 <x<-0.9 _ / J 0.95 A<y<105 A Pmb ‘ >{5/ V 0.95 A<z<105 A 7’rolo {Hal-’5 2 His/24X A)’ AZ Maw”? =W : 4r? Ax: 0.2A 4y :: 0.] :40 42-“— C7.”1 Prob (He) : Z ”[341 Emma/2470M“) 2x05 /+ W?) b) We are given a nano rod which is effectively a 1-D particle in a box. Given that the ground to the first excited state energy is 1 eV, then what is the energy needed to excite an electron from the ground to the second excited state? Ground 5am“ nc/ ~1. where, A . ) En : L1 ”‘2’ .‘: Afil (,3 50W andan‘l‘ OF'I'I‘IJ' JXW 8m]. ): A(z"'/’) ’ 37" “/CV 3) When methane (CH4) burns in air, the temperature rises; this can cause a reaction whereby oxygen molecules 1’ 02) and nitrogen molecules (N2) react to form N02. Say we burn l. 0 gram of methane 1n a container which has 6 0 grams of oxygen and because of that the remainder of the 02 (after burning of the methane) reacts with N2. How many grams of N02 will be produced? ENC/4'1 #202 ‘~> C02 79/420 ' I”? H? 32. 0 _ C217! lmp/ Ch:) 2 mo} 02- J<3______ 9 2): ‘ r "a? 759 0/ [ /me)CHyJ /mo/0 %09m02 [131/9911] 0,.) —— (02. buwn‘d) : (02 /e.,c+) 60 gram; 02 — L/roflrams 02 3 2,03%: 01 ...
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