課程名稱︰普通化學丙
課程性質︰必修
課程教師︰佘瑞琳
開課學院：生命科學院
開課系所︰生科系/生技系
考試日期（年月日）︰2018.1.8
考試時限（分鐘）：100+20(延長)
試題 :
●Constants: R = 8.314 J/mol-K = 0.082 L-atm/mok-K; F = 96500 C/mol
●Equations for reference
△G = △H - T△S △G' -RTlnK △G = △G' + RTlnQ
△G = -nFE E'_cell = (RT/nF)lnK E = E'_cell-(RT/nF)lnQ
I.Problems:(70%)
1. The decomposition of SO_2Cl_2 is first order in SO_2Cl_2 and has a rate constant of 1.42 x 10^-4 s^-1 at a certain temperature. (6%)
(a) If the initial concentration of SO_2Cl_2 is 0.150 M. What is the concentration of SO_2Cl_2 after 2.00 x 10^2 s?
(b) How long will it take for the concentration of SO_2Cl_2 to decrease to 25% of its initial concentration?
(c) What is the half-life of the reaction?
2. The rate constant (k) for a reaction is measured as a function of temperature. A plot of ln k versus 1/T (in K) is linear and has a slope of -7445. Calculate the activation energy for the reaction. (4%)
3. Consider the reaction: I_2(g) + Cl_2(g) ←→2ICl(g) K_p = 81.9 (at 25'c)
A reaction mixture at 25'c initially contains P(I_2) = 0.100 atm, P(Cl_2) = 0.100 atm, and P(ICl) = 0.100 atm. (8%)
(a) Calculate the reaction quotient (Q) of the reaction.
(b) Determine the direction of the reaction.
(c) Find the equilibrium partial pressures of I_2, Cl_2, and ICl at this temperature.
4. Calculate the pH of each of the following solutions: (8%)
(a) 0.10 M Ba(OH)_2,
(b) 0.10 M HBr(aq),
(c) 0.10M HF(aq), K_a for HF(aq) = 1 x 10^-4
(d) 0.10 M NaF(aq)
5. The solubility product constant (K_sp) of an insoluble salt magnesium fluoride, MgF_2, is 1.2 x 10^-12. (6%)
(a) Give the equilibrium constant expression of MgF_2.
(b) Calculate the molar solubility of MgF_2 in pure water.
(c) Calculate the molar solubility of MgF_2 in a 1.0 M NaF solutoin.
6. Methanol burns in oxygen to form carbon dioxide and liquid water. (10%)
(a) Write a balanced equation for the combustion of liquid methanol.
(b) Calculate △H', △S', and △G' at 298 K.
(c) Dose the entropy of the system increase or decrease?
(d) Is the process spontaneous or not at 298 K?
───────────────────────────
298K CH_3OH(l) O_2(g) H_2O(l) CO_2(g)
───────────────────────────
△H'_f (kJ/mol) -238.6 -285.8 -393.5
S' (J/mol-K) 126.8 205.2 70.0 213.8
△G'_f (kJ/mol) -166.6 -237.1 -394.4
───────────────────────────
7. Consider the reaction: CO(g) + 2 H_2(g) ←→CH_3OH(g) K_p = 2.26 x 10^4 at 25'c. (6%)
(a) Calculate △G for the reaction at 25'c under standard states.
(b) Calculate △G for the reaction when the partial pressures are P(H_2) = P(CO) = 0.010 atm, P(CH_3OH) = 1.0 atm.
(c) What is the value of △G at equilibrium?
8. The cell diagram for an electrochemical cell is written as: (10%)
Sn(s)|Sn^2+(aq)||NO(g)|NO_3^-(aq), H^+(aq)|Pt(s).
Sn^2+(aq, 1.0 M) + 2e^- →Sn(s) E' = -0.14 V
NO_3^-(aq, 1.0 M) + 4H^+ + 3e^- → NO(g) + 2H_2O(l) E' = 0.967 V
(a) Indicate the anode and cathode.
(b) Write the balanced overall cell reaction.
(c) What is the value of E'_cell at 298 K?
(d) What is the equilibrium constant K for the reaction at 298 K.
(e) What is the value of E_cell when the reaction is at equilibrium.
9. The Haber process is carried out at 800 K and 300 atm usually. (10%)
For the Haber process at 25'c, N_2(g) + 3H_2(g) ←→2NH_3(g),
△H' = -92 kJ and △S' = -198 J/K. Assume △H' and △S' keep constant.
(a) Calculate △G' at 298 K and 800 K, respectively.
(b) Calculate the equilibrium constant (K) at 298 K and 800 K, respectively.
(c) Briefly explain why the Haber process is carried out at 800 K instead of 298 K.
II. Multiple Choice Questions: (30%)
1. The mechanism shown here is proposed for the gas-phase reaction, 2 N_2O_2(g) →4 NO_2(g) + O_2(g). According to the proposed mechanism, choose the correct statements.
Step 1: N_2O_5 ←→NO_2 + NO_3 (fast)
Step 2: NO_2 + NO_3 →NO_2 + O_2 + NO (slow)
Step 3: NO + N_2O_5 →3 NO_2 (fast)
(a) The proposed rate law is rate = k[N_2O_5].
(b) NO_2 is the intermediate.
(c) NO_3 is the catalyst.
(d) Step 2 is the rate determining step.
2. Which statement is true regarding the function of a catalyst in a chemical reaction?
(a) A catalyst increases the rate of a reaction.
(b) A catalyst provides an alternate mechanism for the reaction.
(c) A catalyst is not consumed by the reaction.
(d) A catalyst could decrease the heat of reaction (△H).
3. Consider the equilibrium: CaCO_3(s) ←→CaO(s) + CO_2(g) △H' > 0, which of the following will shift the equilibrium position to the right?
(a) Add some CaCO_3 to the system.
(b) Add some catalyst to the system.
(c) Increase the volume of the container at constant temperature.
(d) Raise the temperature of the system.
4. The reaction A(g) ←→2B(g) has an equilibrium constant of K = 0.010.
What is the equilibrium constant for the reaction B(g) ←→1/2A(g)
(a) 1 (b) 10 (c) 100 (d) 0.0010
5. Consider a 0.10 M phosphoric acid H_3PO_4(aq), choose the correct statement.
(a) It is a tiprotic acid.
(b) [H^+] = 0.30 M.
(c) [PO_4^3-] = 0.10 M.
(d) This is a strong acid.
6. Which ion forms a basic solution when dissolved in water?
(a) ClO_4- (b) NO_2^- (c) SO_4^2- (d) CH_3COO^-
7. Which of the following is conjugated acid-base pair?
(a) H_2SO_4, SO_4^2- (b) H_3O^+, OH^- (c) NH_4^+, NH_3 (d) ClO_4, ClO_3^-
8. Which of the following salt will form a solution that is acidic?
(a) FeCl_3 (b) CaBr_2 (c) NH_4Br (d) Pb(NO_3)_2
9. Which of the following is a Lewis base?
(a) Cl^- (b) Fe^3+ (c) NH_3 (d) BF_3
10. Calculate the pH of a solution consistiing of 0.050 M C_6H_5OOH(aq) and 0.15 M NaC_6H_5COO. For C_6H_5COOH(aq), K_a = 1.0 x 10^-5.
(a) 1.30 (b) 4.52 (c) 5.00 (d) 5.48
11. To prepare a buffer with pH 9.0, which combination is the best choice?
(a) HCOOH / HCOONa (pK_a = 3.74)
(b) CH_3COOH / CH_3COONa (pK_a = 4.74)
(c) NH_4Cl / NH_3 (pK_b of NH_3 = 4.74)
(d) C_5H_5N / C_5H_5NHCl (pK_b of C_5H_5N = 8.76)
12. The titration curves for the titration of 40.0 ml of 0.10 M monoprotic acid HA(aq) and HB(aq) with 0.10M NaOH are shown as followings. Choose the correct statements.
https://i.imgur.com/ooXo8o7.jpg
(a) HA(aq) is a strong acid.
(b) The pH values at equivalence point for titration of HA(aq) and HB(aq) are about pH 7.0.
(c) HB(aq) is an acid with pK_a = 5.0.
(d) Bromocresol green (pK_In = 5) could be used in the titration of HA(aq) and HB(aq).
13. Which of the following compound is more soluble in acidic solution than in pure water?
(a) BaCO_3 (b) PbI_2 (c) AgCl (d) CuS
14. Which reaction is likely to have a positive entropy change (△S_system > 0).
(a) SiO_2(s) + 3 C(s) →SiC(s) + 2 CO(g)
(b) 6 CO_2(g) + 6 H_2O(g) →C_6H_12O_6(s) + 6 O_2(g)
(c) 3 NO_2(g) + H_2O(l) →2 HNO_3(aq) + NO(g)
(d) CaCO_3(s) →CaO(s) + CO_2(g)
15. Which metal can sever as sacrificial anode to prevent the rustiong of an iron pipe?
(a) Ag (b) Cu (c) Mg (d) Zn