Northern Arizona University Exam #1. Section 2, Spring 2006 February 17, 2006

Transcription

1 Norhern Arizona Universiy Exam # CHM 52, General Chemisry II Dr. Brandon Cruickshank Secion 2, Spring 2006 February 7, 2006 Name ID # INSTRUCTIONS: Code he answers o he True-False and Muliple-Choice quesions on he scanron form. Mark A for rue and B for false. There is only one correc answer for each muliple-choice quesion. There is no parial credi given for his secion. Show all work on he problems secion because parial credi is awarded for his secion. Below your ID# a he op of his page, answer he following quesion. Who is your favorie American Idol hos: Simon, Randy, or Paula? You will receive bonus poin. There are 86 poins on his exam. GOOD LUCK! ENJOY!! PART I: True-false saemens (3 poins each). ΔGf o of an elemen in is sandard sae is zero. T 2. A posiive sign for ΔS rxn indicaes ha he reacion is sponaneous. F 3. A negaive sign for ΔG indicaes ha he reacion is exohermic. F 4. For a second-order reacion, he rae of reacion decreases as reacan is consumed. T PART II: Muliple Choice (3 poins each) 5. Which one of he ses below has he species lised in order of increasing sandard enropy, S? [a] Cr(s) < C 2 H 5 OH(l) < NaHCO 3 (s) < N 2 (g) [b] Cr(s) < NaHCO 3 (s) < C 2 H 5 OH(l) < N 2 (g) [c] N 2 (g) < NaHCO 3 (s) < Cr(s) < C 2 H 5 OH(l) [d] NaHCO 3 (s) < C 2 H 5 OH(l) < Cr(s) < N 2 (g) [e] N 2 (g) < C 2 H 5 OH(l) < NaHCO 3 (s) < Cr(s) 6. Consider he following processes: I. a solid mels II. a vapor condenses o a liquid III. a solid sublimes IV. a liquid freezes Which processes are characerized by a negaive change in enropy? [a] II, III, IV [b] I, II [c] II, IV [d] III, IV [e] I, III

2 Exam Spring 2006 CHM 52, Sec 2 Dr. Cruickshank 7. Use he following daa o calculae ΔS for he reacion: Compound S (J/mol K) H 2 (g) 30.6 N 2 (g) 9.5 NH 3 (g) 92.3 N 2 (g) + 3 H 2 (g) 2 NH 3 (g) [a] 62.5 J/K [b] 29.8 J/K [c] 98.7 J/K [d] 98.7 J/K [e] 29.8 J/K 8. For he following reacion, ΔH 20.2 kj and ΔS +43. J/K. Which of he following saemens abou his reacion is rue? H 2 (g) + S (s) H 2 S (g) [a] he reacion will become sponaneous a higher emperaures. [b] he reacion will become nonsponaneous a higher emperaures. [c] he reacion is no sponaneous. [d] he reacion is always sponaneous. [e] impossible o deermine from he informaion given. 9. The following reacion is no sponaneous a 25 C. Fe 2 O 3 (s) + 3 H 2 (g) 2 Fe (s) + 3 H 2 O (g) If ΔH 98.8 kj and ΔS is 4.5 J/K, calculae he emperaure a which he reacion becomes sponaneous. [a] 432 K [b] 425 K [c] 97 K [d] 698 K [e].43 K 0. Given ha he normal freezing poin of ammonia, NH 3, is 78 C, predic he signs of ΔG, ΔH, and ΔS for ammonia when i freezes a 00 C a am pressure. ΔG ΔH ΔS [a] + [b] + + [c] + + [d] + [e] NH 3 (l) NH 3 (s). Consider he reacion: C 2 H 2 (g) + 2 H 2 (g) C 2 H 6 (g) If C 2 H 6 is appearing a a rae of 2.0 M/s, a wha rae is H 2 disappearing. [a] 2.0 M/s [b] 4.0 M/s [c] 8.0 M/s [d] 0.5 M/s [e].0 M/s 2. A paricular reacion has he following unis for he rae consan, k:. Wha is he order of he reacion? 3 M s [a] 2 nd [b] 3 rd [c] 4 h [d] s [e] no enough informaion o deermine (2)

3 Spring 2006 Exam Dr. Cruickshank CHM 52, Sec 2 3. Which one of he following would aler he value of he rae consan (k) for he reacion: 2 A + B producs [a] increasing he emperaure. [b] measuring k again afer he reacion had run for a while. [c] increasing he concenraion of A. [d] increasing he concenraion of B. [e] all of hese would aler he rae consan. 4. The rae of a zero-order reacion: [a] decreases as reacan is consumed. [b] is independen of emperaure. [c] is independen of he concenraions of reacans and producs. [d] increases as reacan is consumed. [e] depends on he concenraion of producs. 5. A reacion has he rae law, Rae k[a][b] 2. Which one of he following changes will cause he greaes increase in he reacion rae? [a] doubling he concenraion of [A] [b] increasing he concenraion of [A] by a facor of 8 [c] ripling he concenraion of [B] [d] decreasing he emperaure wihou changing he concenraions [e] doubling he concenraion of [B] 6. Consider he reacion, A producs. A plo of [A] versus ime produces a sraigh line. Which of he following saemens is rue? [a] he rae of he reacion does no depend on he concenraion of A. [b] he reacion is second order. [c] he iniial concenraion of A can be calculaed from he inercep on he x-axis. [d] he rae consan for he reacion can be obained from he value of he inercep on he y-axis. [e] he rae consan is equal o he negaive of he slope. 7. For he reacion, X + Y Z, he reacion rae is found o depend only upon he concenraion of X. A plo of /[X] versus ime gives a sraigh line. Wha is he rae law for his reacion? [a] rae k[x][y] [b] rae k[x] 2 [Y] [c] rae k[y] [d] rae k[x] [e] rae k[x] 2 8. Consider he following second-order reacion a 35 C. NOCl (g) NO (g) + /2 Cl 2 (g) Wih an iniial concenraion of [NOCl] M, he concenraion of NOCl drops o 3.74 M afer 60.0 minues. Calculae he half-life for his reacion. [a] min [b] 86 min [c] 268 min [d] min [e] 32 min (3)

4 Exam Spring 2006 CHM 52, Sec 2 Dr. Cruickshank 9. Below is a plo of k versus /T for he reacion N 2 O 5 (g) 2 N 2 O 4 (g) + O 2 (g) k vs /T k slope K Based on his informaion, he acivaion energy, E a, for his reacion is: [a] 43 J/mol [b] 79.0 kj/mol [c] 79.0 J/mol [d] J/mol [e] 43 kj/mol T 20. Which of he following seups would allow he calculaion of he acivaion energy, E a, of a reacion which has k /s a 20 C and k /s a 26 C? [a] [c] Ea Ea [e] none of hese [b] [d] Ea Ea According o collision heory, all collisions do no lead o produc formaion. Which choice gives he reasons why all collisions beween reacan molecules do no lead o produc formaion? I. The oal energy of he colliding molecules is less han some minimum amoun of energy. II. Molecules canno reac wih each oher unless a caalys is presen. III. Molecules can only collide if hey are in he same phase. IV. Molecules ha are improperly oriened during collision may no reac. [a] I and IV [b] I and III [c] III and IV [d] I and II [e] II and III 22. For he reacion, A + B producs, he experimenally deermined rae law is: Rae k[b] 2. If I indicaes an inermediae and P indicaes a produc, which of he following is he mos likely reacion mechanism? [a] B + B I (slow) [b] A + B I (fas) [c] A + B C (slow) A + I P + B (fas) I + B P (slow) C P (fas) [d] B + B I (slow) A + I P (fas) [e] A + B P (one sep) (4)

5 Spring 2006 Exam Dr. Cruickshank CHM 52, Sec 2 PART III: Problems 23. Consider he following reacion 3 B + C E + 2 F for which he following rae daa were obained. Experimen [B] (M) [C] (M) Rae (M/s) [a] Deermine he rae law for his reacion. SHOW WORK! [3 ps] Exp. and 2: Exp. and 3 Rae 2 Rae x [C] 2 x [C] x M M M M /s /s 0.00 Rae 3 Rae [B] [B] y 3 y M/s M M/s M y 2 2 x 9 3 y x y 2 Rae k[b] 2 [C] [b] Calculae he rae consan, k, for his reacion. [2 ps] Rae k[b] 2 [C] Rae k(0.250 M) 2 (0.00 M) k /M 2 s [c] Calculae he rae of he reacion if [B] M and [C] 0.00 M? [2 ps] Rae k[b] 2 [C] Rae ( /M 2 s)( M) 2 (0.00 M) Rae M/s (5)

6 Exam Spring 2006 CHM 52, Sec 2 Dr. Cruickshank 24. The rae consan, k, for he reacion, A B, is s. [a] Calculae he half-life, /2, for his reacion. [2 ps] k s 38.5 s [b] If he iniial concenraion of A is 0.55 M, wha is he concenraion of A afer 4.0 minues? [4 ps] [A] k + [A] 0 [A] ( /s)(240 s) + (0.55) [A] [A] e e [A] M 25. Consider a reacion a 25 C for which ΔH sys 28 kj/mol and ΔS sys 98 J/K mol. [a] Calculae ΔS univ. [4 ps] ΔS univ ΔS sys + ΔS surr ΔH 3 sys ( 28 0 J/mol) Δ Ssurr J/K mol T 298 K ΔS univ 98 J/K mol J/K mol 4.0 J/K mol [b] Is he reacion sponaneous a 25 C? Your response mus be based on your answer o par (a). [2 ps] No. The reacion is no sponaneous. The 2 nd Law of Thermodynamics saes ha he enropy of he universe increases in a sponaneous process. (6)

7 Spring 2006 Exam Dr. Cruickshank CHM 52, Sec 2 Poenially Useful Informaion o o o Δ[conc] Rae Δ o o o Δ H ΣnΔH (producs) ΣnΔH (reacans) Rae k[a] x [B] y Δ Grxn ΣnΔGf (producs) ΣnGf (reacans) rxn f f o o o Δ Srxn ΣnS (producs) ΣnS (reacans) [A] k + [A] 0 ΔG ΔH TΔS [A] k + [A] 0 K C [A] k [A] 0 ΔS univ ΔS sys + ΔS surr k + [A] [A] ΔHsys Δ Ssurr T mol solue Lso k k[a] M 2 0 Ea k + A R T R 8.34 J/mol K a k E k2 R T2 T 0 (7)