CHM 122. EXAM 2 MWF 8:00AM 8:50AM March 6 th Bronco ID. Question Score Possible Points. 1 (16pts) 2 (31pts) 3 (37pts) 4...

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1 CHM 122 EXAM 2 MWF 8:00AM 8:50AM March 6 th 2015 Name Bronco ID. Question Score Possible Points 1 (16pts) 2 (31pts) 3 (37pts) 4... (16pts). Total (100pts) 1. Read each question carefully. Make sure you are answering the question which is being asked. Write your answer clearly and do not use notation such as to show your answer 2. Answer easier questions first, more difficult questions later 3. Ask the instructor for clarification if you are puzzled by the question 4. Show work for credit. Use dimensional analysis by meant of using an appropriate stiochiometry to prove your solution. Watch for significant figures. 5. Any forms of cheating will be an automatic F 6. GOOD LUCK Dang1

2 Question I Multiple choices ( Choose one best answer for each question) (20pts) 1. Which of the following are TRUE? A) An effective buffer has a [base]/[acid] ratio in the range of B) A buffer is most resistant to ph change when [acid] = [conjugate base] C) An effective buffer has very small absolute concentrations of acid and conjugate base. D) A buffer can not be destroyed by adding too much strong base. It can only be destroyed by adding too much strong acid. 2. Which of the following solutions is a good buffer system? A) A solution that is 0.10 M NaCl and 0.10 M HCl B) A solution that is 0.10 M HCN and 0.10 M LiCN C) A solution that is 0.10 M NaOH and 0.10 M HNO 3 D) A solution that is 0.10 M HNO 3 and 0.10 M KNO 3 3. Buffer solutions A) will always have a ph of 7. B) are rarely found in living systems. C) cause a decrease in ph when acids are added to them. D) tend to maintain a relatively constant ph. E) cause an increase in ph when acids are added to them. 4. Which of the following signs on q and w represent a system that is doing work on the surroundings, as well as losing heat to the surroundings? A) q = -, w = - B) q = +, w = + C) q = -, w = + D) q = +, w = - Dang2

3 5. A process is carried out at constant pressure. Given that ΔE is positive and ΔH is negative, A) the system absorbs heat and expands during the process. B) the system absorbs heat and contracts during the process. C) the system loses heat and expands during the process. D) the system loses heat and contracts during the process The following drawing is a representation of the exothermic reaction in which ozone forms dioxygen. 6. What are the signs of ΔH and ΔS for this reaction? A) ΔH = +, ΔS = + B) ΔH = +, ΔS = - C) ΔH = -, ΔS = + D) ΔH = -, ΔS = - 7. This reaction is likely to be A) nonspontaneous at all temperatures. B) nonspontaneous at low temperatures and spontaneous at high temperatures. C) spontaneous at low temperatures and nonspontaneous at high temperatures. D) spontaneous at all temperatures 8. The specific heat of copper is J/g o C If 34.2 g of copper, initially at 25 o C, absorb kj, what will be the final temperature A) 25.4 o C B) 27.8 o C C) 356 o C D) 381 o C Dang3

4 Question II 30 pts 1. (6pts) Fill in the blanks A spontaneous reaction has a value of G and is favored by a value of H and a value of S. 2. (6pts) Explain the difference between ΔH and ΔE 3. (6pts) What is 2 nd Law and 3 rd Law of Thermodynamic 4. (13pts) Consider the two reactions below then complete the table and the graphs 4Fe + 3O 2 2Fe 2O 3 C + H 2O CO + H 2 H rxn = kj H rxn = kj Type of Reaction Sign (+ or -) of H rxn Which has more energy: reactants or products? Exothermic Endothermic Make enthalpy diagrams for the two chemical reactions from above, showing clearly the amount of energy released or gained. Exothermic Change Endothermic Change E n er g y Time Dang4 E n e r g y Time

5 Question III-37points 1. ( 10pts) Determine the enthalpy H rxn using Hess' Law of formation for MnO 2 (s) Mn (s) + O 2 (g) > MnO 2 (s) Given: 4 Al (s) + 3 O 2 (g) > 2 Al 2O 3 (s) H rxn = kj/mol 4 Al (s) + 3 MnO 2 (s) > 3 Mn (s) + 2 Al 2O 3 (s) H rxn = kj/mol 2. Consider this reaction Ni(s) + 4 CO(g) Ni(CO) 4(g) Ni(s) CO(g) Ni(CO) 4(g) ΔH o f (kj/mol) S o (J/mol K) a. (16pts) Calculate H o (kj), S o total (J//K) and G o (kj) for this reaction at 25 o C b. (3pts) Is the reaction spontaneous at this standard condition? c. (8pts) Calculate K p for this reaction. R = J/mol K Dang5

6 Question IV-16 points 1. (16pts) A 1.00 L buffer solution is M in HC7H5O2 and M in LiC7H5O2. Show an acid dissociation equation, neutralization reaction with the changing table to receive Full Credit a. Use Henderson-Hassalbalch to calculate the initial ph of this buffer solution b. Calculate the ph of the solution after the addition of ml of 1.00 M HCl. The Ka for HC7H5O2 is Bonus: (5pts) According to the following thermochemical equation, what mass of HF (in g) must react in order to produce 345 kj of energy? Assume excess SiO 2. SiO 2(s) + 4 HF(g) SiF 4(g) + 2 H 2O(l) ΔH rxn = -184 kj Dang6