Problems 24-37: Write only the answer in the indicated space

Problems 24-37: Write only the answer in the indicated space. 1. (2 pts.) According to the following reaction, determine which substance is reduced and which is oxidized. I− + MnO−4 + H+ → I2 + MnO2 + H2O reduced ________________________ 2. oxidized ________________________ (2 pts.) According to the following reaction, determine which substance is reducing and oxidizing agent. Cr2O27− + 6 S2O23− + 14 H+ → 2Cr3+ + 3 S4O26− + 7 H2O reducing agent ________________________ 3. oxidizing agent ________________________ (2 pts.) At what temperature (°C) will a reaction have ΔG = 0 if ΔH = -24.2 kJ/mol and ΔS = -55.5 J/Kmol? __________________ 4. (2 pts.) What is the value of ΔS° ) for the following reaction? 200.8, for C2H6 (g) is 229.5, and for H (g) is 130.58? f ) for C2H2 (g) is C2H2 (g) + 2H2 (g) → C __________________ 5. (2 pts.) Determine the signs (+, - or 0) of ΔH° and ΔS° if the reaction is spontaneous at high temperatures but nonspontaneous at low temperatures. ΔH° ________________________ 6. 7. ΔS° ________________________ (3 pts.) Determine the oxidation number for each element in the following substances. KMnO4 K : ___________ Cr : ___________ O : ___________ Zn3(PO4)2 Zn : ___________ P : ___________ O : ___________ (3 pts.) ?????° of the reaction is -0.55 V. Determine the value of ?G° for the reaction, in kJ/mol. I2 (s) + 2Br− (aq) → 2I− (aq) + Br2 (l) __________________ 8. (3 pts.) Write the balanced overall reaction. Sn (s) | Sn2+ (aq) | | NO−3 (aq) | NO Pt _______________________________________________________________________________________________ How many moles of electrons are transferred? _______________ 9. (5 pts.) Cobalt-60 is produced by a three reaction process involving neutron capture, beta-emission, and neutron capture. Starting with the initial reactant, write the reaction for each step of this process. 1st reaction _________________________________________________________ 2nd reaction _________________________________________________________ 3rd reaction _________________________________________________________ 10. (2 pts.) Determine the missing reactant. _____________ 10B + _____ → 137N + 10n 5 11. (2 pts.) How many neutrons are emitted when a californium-249 is bombarded with C-12 to produce a Rf − 257? ___________________ 12. (2 pts.) Identify the correct definition by circling one of the answers. a) For any spontaneous process, the entropy of the First universe increases. b) The energy is not created or destroyed. First Second Third Second Third Entropy Free energy d) The spontaneity of the reaction. Enthalpy Entropy 210 13. (3 pts.) Determine the mode of decay for 84Po and write the decay reaction. Free energy c) The disorder of the reaction. Enthalpy Mode of decay: ____________________________________________________ Decay reaction: ____________________________________________________ 14. (3 pts.) Complete the following reactions, and determine the type of reaction (alpha emission, beta emission, positron emission, electron capture or gamma emission). Rb + ________ __________________________________ 2 Kr → Si + ________ __________________________________ P→ For problems 38-45, write legible and stepwise (complete) solutions, and show all the work to receive full credit. Maximum points are awarded for correct answer with units, and no points if only the final answer is written. 15. (5 pts.) Consider the reaction between ammonia and hydrochloric acid to produce ammonium chloride. Given the following table of thermodynamic data at 298 K, determine the value of K for the reaction at 25 °C. 16. (5 pts.) The normal boiling point of water is 100.0 °C and its molar enthalpy of vaporization is 40.67 kJ/mol. What is the change in entropy in the system in J/K when 24.7 grams of steam at 1 atm condenses to a liquid at the normal boiling point? 3 ) Consider the redox reaction indicated by the following line notation: Pb a) Write the balanced half-reaction that occurs at the cathode. b) Write the balanced half-reaction that occurs at the anode. c) Write the balanced overall-reaction. d) Using the table of half-reaction potentials (on page 10), calculate Ecell° . e) (Circle one) Under standard state conditions, the reaction is spontaneous or nonspontaneous. Considering the same redox reaction with following concentrations Pb f) Calculate Ecell at 25°C. g) (Circle one) According to Ecell, the reaction is: spontaneous or nonspontaneous. h) (Circle one) If the concentration of Pb2+ was increased to 2.0 M, Ecell would increase or decrease. 41. (5 pts.) Balance the redox reaction in basic solution. Cr2O27−(aq) + HNO2(aq) → Cr3+(aq) + NO−3 (aq) 4 42. (6 pts.) Consider the following half-reactions: PbO2 + 4H+ + SO24− + 2e− → PbSO4 + 2H2O Ered° = 1.69 V PbO2 + 4H+ + 2e− → Pb2+ + 2H2O Ered° = 1.46 V a) Calculate the solubility product constant, Ksp, of PbSO4 at 25°C. b) (Circle one) Under standard state conditions, reaction is: spontaneous or nonspontaneous. c) (Circle one) This electrochemical cell is: voltaic or electrolytic d) What is the value of Ecell at equilibrium? 43. (5 pts.) How many grams of Cu are obtained by passing a current of 12 A through a solution of CuSO 4 for 15 minutes? 5 44. (5 pts.) The half-life of carbon-11 is 20.3 minutes. How much of a 100.0 mg sample remains after 1.50 hours? 45. (5 pts.) Strontium-90 is a byproduct in nuclear reactor fueled by the radioisotope uranium-235. The half-life of strontium-90 is 28.8 yr. What percentage of strontium-90 sample remains after 75.0 years? Possibly useful constants and equations ?S = ?Hsystem system ?G = ?G° + RTln Q ° Ecell = Ecell − charge = current × time T ?G° = −RT ln K 0.0592 log(Q) ?G° = −nFEcell° Ecell° = 0.0592n log (K) n 6 0.693 t Rate = k[N] ln = −kt ln[N]t = −kt + ln[N]0 k 0 J R mol t1/2 = CJ K 1 F = 96,485 mol e− mol e 7 8