CHEM120-Midterm4

CHEM120-Midterm4 - Univnrslly at University of Waterloo...

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Unformatted text preview: Univnrslly at University of Waterloo Waterloo DEPARTMENT or CHEMISTRY W CHEM 120 — Term Test #2 Q Friday, November 19, 2004 Name (Print clearly): Last name h First nan-1 ' Student Number: Signature: Time Allowed; 50 minutes Aids Allowed: Electronic Calculator Instructions: 1. The instructors" names and section numbers are given below. Circle your instructor‘s name and section number now. R. J. Le Roy M. Chong __ "C. Bissonnette 1C. Bissonnette section 002 Section 003 Section 004 _ .-" Section 005 9:30 am 10:30am 11:30am 12:30 pm 2. This test booklet has 10 questions and 7 pages (including this Cover Page and the Data Sheet). If pages are missing, raise your hand and ask for a new test booklet. 3. Each question is worth three (3) marks. Part marks may be awarded. 4. Work out your answer to each question in the space provided. If you need extra space use the back of the preceding page. Write your final answer in the answer box. i. 5. Do all rough work on this test booklet. Scrap paper is not permitted. 6. At the end of the test, turn in this test booklet and the data sheet and then leave immediatelv. Note: The last page is a DATA SHEET. You may tear it off. Return the Data Sheet with your test booklet. Do 0! write in this box. 3 CHEM 120 (Fall 2004) Test #2 Page 2 of 7 1. It takes 22.0 minutes for a lOAO-mL sample of an unknown gas to eficuse through a pinhole. A l0.0-mL sample of helium, He, required 450 minutes. What is the molar mass, MM, ofthe unknown gas? aim - (.3? cw” :- u H , ,-j,ar;/ ;,¢.‘.' IL 7 'rl__ , I r {riff} If: _ r I'll! ’ h" l r I C r i I I ; / I I , \‘ L} f j i /f."‘ '. J'_ - J \J’ 7 ,f I; x '\ H . C] .\_ i i: r I.» I .r b 7 ' 4' 2 Given the following thermochemical equations, HF(g) a» H(g) + Hg) AH" = 568 kJ (per mol HF) '. ,4 " H2(g) —> 2 l'l(g) AH° = 436 kJ (per mol H2) HHg) -—-» v2 H2(g) + ‘/2 mg) AH" = 271 1:] (per mol HF) what is for the reaction below? mg) e F2(g) / ‘ a; f a 4 v I 3% V [W X H ’ J” '2 l ‘ ‘rlda 153/3 l" a) ' ‘ ‘ < ’ Brit it: 0 r’é) v---- ' ' 12:; ; / FF") _‘= ~ I F: k] (per mol F2) CHEM 120 (Fall 2004) Test #2 Page 3 of 7 a a. The heat capacities of iron and liquid water are 0.449 J g"! K"l and 4.184 J g 1 K 1, respectively. What is the final temperature of the iron-water mixture if a 100.0-g sample of iron, initially at 85.0“C, is added to 50.0 g ofwater, initially at 250°C? NV 5T J". I}: t / / 1 -..-.~ n p ’ “ " 7/ “glib/‘(ljra—I/k ,*~ {lyogu ’x/f"lr - 55 B/IJ 193.1% # 2113.33): J $51,? 7!, 4 “figs-3a; “3” ‘ 71’ ’ Iggthf " “3'93” ~,-{'2 H293 (I I"?! 7?"'{_53 It; 7;: 309 ?: K :02./,' 7*?5’5 = 33g ’< 4. A sample of gas absorbs exactly 675 J of heat from its surroundings. At the same time‘ the gas expands from 3.55 L to 13.15 L against a constant external pressure of0.962 atm. What is the internal energy change, AU; for the gas? Give your answer injeules. .J l/‘qy . 5‘. U .l J III ‘ .. "'1', I".- —":. .3 - _ .-—r r' ’ ’ 4' J - fat)“ L h I. U1 l J’ ()2 z 4 [J'- .. fl ~. . f ‘ K S} ( , ELI-f I) L/ g) CHEM 120 (Fall 2004) Test #2 Page 4 of 7 5. The standard enthalpy change for the reaction below is AH" = —905.4 kl. What is AH:- for N0(g).O 4 NI-l3(g) + 5 02(g) —> 4N0(g) v. 6 H20(g) Substance AH:- (in kJ mol ‘) '-i f- “ A“: A Wag) —46.1 "ax-595% ’ UD '% (ii/H “H: g) ,._ H200?) ""2418 [F think/+1 5 6. Light with a wavelength of259 nm causes electrons to be ejected from the surface of a magnesium metal with a maximum kinetic energy of 1.806x10'191. What is the longest \Wa elength oflight that can be used to dislodge electrons from the surface of magnesium? CHEM 120 (Fall 2004) Test #2 Page 5 of 7 7. The following statements concern an isolated H atom. Classify each statement as true (T) or false (F). (0.5 marks each) The most probable radial distance, r. between the electron and the nucleus corresponds to the position of the maximum in a plot of R1 versus r, where R is the radial part of ‘l’ .' T. Each line in the line spectrum ofthe H atom corresponds to the energy difference between a specific pair of electron orbitals. " _._._..._ mi For the 3d);‘ orbital, there is zero probability of finding the electron in the xy plane. For an H atom, the energy ofthe 3s orbital is equal to that ofa 3p orbital. The probability of finding an electron at a point is equal to the value of ‘l’ at that point. I 'T For an electron in the ls orbital. the total energy of the electron decreases as the radial I i ,_ distance. r, decreases. ' ; l 8. Answer the following questions. (05 marks each) i r: How many electrons does it take to fill the n = 3 shell ’9 i _ _._... d i How many electrons does it take to fill the 4f subshell‘? l Egg i True (T) or False (F)? An acceptable set of quantum numbers for an electron in an atom is F ;n=2.l=05m;= l.andm_t=—‘/2, True (T) or False (F)? According the Aufbau procedures the 3d orbital fills before 45. ; True (T) or False (F)? For an isolated atom that has an unfilled subshell, the electronic l configuration of lowest energy is the one having the smallest number of unpaired electrons. The radial probability distribution for an orbital in the n '-“- 4 shell is shown below. Which orbital is it? 41tr3R2 CHEM 120 (Fall 2004) Test #2 Page 6 of 7 9. Ifthe electron in a hydrogen atom undergoes a transition from an n = 6 level to an n = 2 level what is the wavelength of the radiation emitted? Give your answer in nanometresx nm. (1 nm= 1x10‘9 m) ,— - $3.; “In! _ .-u_r I“. I .C“ ? - r ' '{'_ ,_ . y .r‘ J‘ilw x? Iflgfif‘ . ____|____________ _ _____________F 9 r3 ' T? a, . hi. is. J' __, ‘ 1;.) "3'! r- , :{3 ’ . I - I’ .. gt 9 ‘- 1 O ' I . \. r. If f- t ‘_ ‘\ . V. , f.- _ q 3 ' . . 2-. :‘x‘\."_ it; mew. a i 131;; ' ____,__.. ...|.-,--d— "' "' _.;_. _ _ 1' E? <1 'I '3 ' ' ' L}- 1? D “J 57:! u {If Hi {I So Hf; 10. The atomic number of cobalt, Co._ is Z :-‘- 27. (3.) According to the Aufbau procedure, what is the ground state electron configuration of Co? (2 marks) If)?! at: ha.“ y ) (b) For an isolated Co atom in its ground electronic state how many unpaired electrons are there? (1 mark) 7 n ‘tL Q “i U ? ...
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CHEM120-Midterm4 - Univnrslly at University of Waterloo...

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