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UT CH 301 - CH301 Practice Exam 3

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CH301 Practice Exam 3 1. Theory: First Law of Thermodynamic Which of the following statements is/are true concerning the first law of thermodynamics? I. The internal energy of the universe may increase, decrease, or stay the same for a given process, depending on the changes in enthalpy and entropy. II. Chemists often consider the universe to be made up of two things: the system and the surroundings (aka everything in existence other than the system) III. If the energy of a system increases, then the energy of the surroundings must also increase to compensate. 1. I only 2. II only 3. III only 4. I and II 5. I and III 6. II and III 7. I, II and III 2. Definition: Enthalpy Which of the following is not a correct description of enthalpy or change in enthalpy? 1. In the absence of gas, ΔH ~ ΔE. 2. ΔH = q in a closed system. 3. Enthalpy is an indirect measure of the change in entropy of the surroundings. 4. In an open system, ΔH = q so the change in enthalpy is a path function, not a state function. 3. Signs for thermodynamic quantities Ice melts at 50 °C, changing from ice (s) to water (l). Which of the following statements about the signs of the process are true? I. Work w is positive (but small). II. Heat q is positive. III. The change in free energy is positive. IV. The change in entropy is positive. 1. I only 2. III only 3. IV only 4. I and II 5. III and IV 6. I, II and IV 4. Definition: state functions Which of the following quantities is not a path function? Choose the best answer. 1. Both enthalpy (H) and pressure (P). 2. work (w) 3. enthalpy (H) 4. pressure (P) 5. Both heat (q) and work (w). 6. heat (q) 7. Both enthalpy (H) and heat (q).5. Definition: Heats of formation Which of the following reactions is an enthalpy of formation reaction? 1. 2K(s) + F2(g) Æ 2KF(s) 2. K(g) + 1/2F2(g) Æ KF(s) 3. K(s) + 1/2F2(g) Æ KF(s) 4. KF(s) Æ K(s) + 1/2F2(g) 6. Definition: Heat capacity It will take ____ (more/less) energy to raise the temperature of 10 g of water than 1 g of nickel because _____________? 1. more; it has a higher specific heat capacity and more mass 2. more; it has a higher specific heat capacity 3. less; it has a lower specific heat capacity and more mass 4. less; it has more mass 7. Calculation: Bomb calorimeter You set up a bomb calorimetry experiment using 2 liter of water as your heat sink and combust a 12.2122 g sample of benzoic acid (C6H5COOH). If the initial and final temperature are 10.00 °C and 48.57 °C respectively, what is the molar enthalpy of combustion of benzoic acid? (Assume the calorimeter itself absorbs no heat [aka the heat capacity of the calorimeter is zero] and assume the density of water is 1 g·mL). Remember that the specific heat capacity of water is 4.184 J g-1 K-1. 1. -3,228 J·mol-1 2. -322.8 kJ·mol-1 3. -322.8 J·mol-1 4. -3,228 kJ·mol-1 5. -32.28 kJ·mol-1 8. Calculation: Hess’ Law and heats of formation Which of the following correctly mathematically describe how to calculate ΔHrxn for the following generalized reaction? A + 2B  3C + D 1. ΔHrxn = [ΔHf (C) + ΔHf (D) ] – [ΔHf (A) + ΔHf (B)] 2. ΔHrxn = [1*ΔHf (C) + 2*ΔHf (D) ] – [3*ΔHf (A) + 1*ΔHf (B)] 3. ΔHrxn = [3*ΔHf (A) + 1*ΔHf (B) ] – [1*ΔHf (C) + 2*ΔHf (D)] 4. ΔHrxn = [1*ΔHf (A) + 2*ΔHf (B)] – [3*ΔHf (C) + 1*ΔHf (D)] 5. ΔHrxn = [3*ΔHf (C) + 1*ΔHf (D) ] – [1*ΔHf (A) + 2*ΔHf (B)] 9. Calculation: Hess’s Law and combined reaction enthalpies Given the following data: CH2CO(g) + 2O2(g)  2CO2(g) + H2O (g) ΔH = -981.1 kJ·mol-1 CH4(g) + 2 O2(g)  CO2(g) + 2H2O (g) ΔH = -802.3 kJ·mol-1 calculate ΔH for the reaction 2CH4(g) + 2O2(g)  CH2CO(g) + 3H2O(g) 1. -623.5 kJ·mol-1 2. 623.5 kJ·mol-1 3. -1783.4 kJ·mol-1 4. 1783.4 kJ·mol-1 5. 178.8 kJ·mol-110. Calculation: Statistical mechanics determination of internal energy How much energy would be associated with the motion of 2.5 moles of methane (CH4)? 1. 3.75RT 2. 3.75kT 3. 18.75RT 4. 18.75kT 5. 7.5kT 11. Calculation: Bond energies You will need the following data C-C 348 kJ mol-1 C-H 413 kJ mol-1 O=O 498 kJ mol-1 C=O 728 kJ mol-1 O-H 463 kJ mol-1 Using bond enthalpy data, calculate the change in enthalpy for the following reaction. C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) 1. -1322 kJ mol-1 2. 1322 kJ·mol-1 3. -496 kJ·mol-1 4. 496 kJ·mol-1 5. 1582 kJ·mol-1 6. -1582 kJ·mol-1 12. Calculation: Work calculation Consider the hypothetical reaction below and approximate the value of the work function at room temperature. 18A(l) + 5B(g)  6C(g) + 14D(l) 1. 2.5 kJ 2. 5 kJ 3. -2.5 kJ 4. -5 kJ 5. 0 kJ 13. Definition: Internal Energy Which of the following is not a definition of internal energy or change in internal energy? 1. An intensive path function. 2. ΔU = qV 3. The difference between the final and initial internal energy of a system. 4. ΔU = q + w 14. Theory: Calorimetry Which of the following statements concerning calorimetry is/are true? I. One calorie is the same thing as one Calorie. II. Calorimetry is done at constant volume. III. In real life, we must compensate for heat lost to the calorimeter. 1. I only 2. II only 3. III only 4. I and II 5. I and III 6. II and III only15. Calculation: Internal Energy calculation (q and w) If the car from the Jetsons does 11000 kJ of work and absorbs 10 kJ of heat (it’s the FUTURE, anything could happen…), what is the change in internal energy for the car? 1. -10990 kJ 2. +11010 kJ 3. 10990 kJ 4. -11010 kJ 16. Ranking: Predicting entropy change in a chemical reaction Rank the following reactions from least to greatest in terms of change in entropy (ΔSrxn): a. 2H2(g) + O2(g)  2H2O(s) b. 2Na(s) + O2(g)  2NaO(s) c. C6H12O6(s) + 6O2(g)  6H2O(g) + 6CO2(g) d. MgCO3(s)  MgO(s) + CO2(g) 1. a<c<b<d 2. a<b<d<c 3. c<d<b<a 4. d<b<c<a 17. Calculation: Entropy change at a phase transition An unknown compound X was discovered on mars. The standard molar entropy is 300 J·mol-1·K-1 for X(g), 100 J·mol-1·K-1 for X(l), and 30 J·mol-1·K-1 for X(s),. What is the change in entropy for the melting of X? 1. 70 J·mol-1·K-1 2. -100 J·mol-1·K-1 3. -80 J·mol-1·K-1 4. -500 J·mol-1·K-1 18. Theory: Second and Third Laws of Thermodynamic Which of the following statements concerning the second and third laws of thermodynamics is/are true?


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UT CH 301 - CH301 Practice Exam 3

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