Thermochemistry Problems

Thermochemistry Problems Answers to problems. 1. A 2. -2512 kJ/mol 3. D 4. A 5. E 6. A 7. D 8. E 9. C 10. C 11. C 12. A 13. B 14. D 15. A 16. C 17. E 18. D 19. B 20. B 21. D 22. D 23. A 24. A 1. Coal gasification can be represented by the equation: 2 C(s) + 2 H2O(g) → CH4(g) + CO2(g) ΔH = ? Use the following information to find ΔH for the reaction above. CO(g) + H2(g) → C(s) + H2O(g) ΔH = -131 kJ CO(g) + H2O(g) → CO2(g) + H2(g) ΔH = -41 kJ CO(g) + 3 H2(g) → CH4(g) + H2O(g) ΔH = -206 kJ A) 15 kJ B) 116 kJ C) -116 kJ D) -372 kJ 2. Acetylene torches utilize the following reaction: 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g) Use the given standard enthalpies of formation to calculate ΔH° for this reaction. 3. The specific heat of copper is 0.385 J/(g ∙°C). If 34.2 g of copper, initially at 25°C, absorbs 4.689 kJ, what will be the final temperature of the copper? A) 25.4°C B) 27.8°C C) 356°C D) 381°C 4. The internal energy of a system is always increased by ________. A) adding heat to the system B) having the system do work on the surroundings C) withdrawing heat from the system D) adding heat to the system and having the system do work on the surroundings E) a volume decompression 5. Which one of the following is an endothermic process? A) ice melting B) water freezing C) boiling soup D) Hydrochloric acid and barium hydroxide are mixed at 25 °C: the temperature increases. E) Both A and C 6. Of the following, which one is a state function? A) H B) q C) w D) heat E) none of the above 7. Which of the following is a statement of the first law of thermodynamics? A) Ek = mv2 B) A negative ΔH corresponds to an exothermic process. C) ΔE = Efinal - Einitial D) Energy lost by the system must be gained by the surroundings. E) 1 cal = 4.184 J (exactly) 8. ΔH for an endothermic process is ________ while ΔH for an exothermic process is ________. A) zero, positive B) zero, negative C) positive, zero D) negative, positive E) positive, negative 9. Which one of the following statements is true? A) Enthalpy is an intensive property. B) The enthalpy change for a reaction is independent of the state of the reactants and products. C) Enthalpy is a state function. D) H is the value of q measured under conditions of constant volume. E) The enthalpy change of a reaction is the reciprocal of the ΔH of the reverse reaction. 10. The reaction 4Al (s) + 3O2 (g) → 2 Al2O3 (s) ΔH° = -3351 kJ is ________, and therefore heat is ________ by the reaction. A) endothermic, released B) endothermic, absorbed C) exothermic, released D) exothermic, absorbed E) thermoneutral, neither released nor absorbed 11. The units of specific heat are ________. A) K/J or °C/J B) J/K or J/°C C) J/g-K or J/g-°C D) J/mol E) g-K/J or g-°C/J 12. Which of the following is a statement of Hess's law? A) If a reaction is carried out in a series of steps, the ΔH for the reaction will equal the sum of the enthalpy changes for the individual steps. B) If a reaction is carried out in a series of steps, the ΔH for the reaction will equal the product of the enthalpy changes for the individual steps. C) The ΔH for a process in the forward direction is equal in magnitude and opposite in sign to the ΔH for the process in the reverse direction. D) The ΔH for a process in the forward direction is equal to the ΔH for the process in the reverse direction. E) The ΔH of a reaction depends on the physical states of the reactants and products. 13. For which one of the following reactions is ΔH°rxn equal to the heat of formation of the product? A) N2 (g) + 3H2 (g) → 2NH3 (g) B) (1/2)N2 (g) + O2 (g) → NO2(g) C) 6C (s) + 6H (g) → C6H6 (l) D) P (g) + 4H (g) + Br (g) → PH4Br (l) E) 12C (g) + 11H2 (g) + 11O (g) → C6H22O11 (g) 14. Of the following, ΔH°f is not zero for ________. A) O2 (g) B) C (graphite) C) N2 (g) D) F2 (s) E) Cl2 (g) 15. Consider the following two reactions: A → 2B A→C ΔH°rxn = 456.7 kJ/mol ΔH°rxn = -22.1 kJ/mol Determine the enthalpy change for the process: 2B → C A) -478.8 kJ/mol B) -434.6 kJ/mol C) 434.6 kJ/mol D) 478.8 kJ/mol E) More information is needed to solve the problem. 16. Calculate the kinetic energy in J of an electron moving at 6.00 × 106 m/s. The mass of an electron is 9.11 × 10-28 g. A) 4.98 × 10-48 J B) 3.28 × 10-14 J C) 1.64 × 10-17 J D) 2.49 × 10-48 J E) 6.56 × 10-14 J 17. A 100-watt electric incandescent light bulb consumes ________ J of energy in 24 hours. [1 Watt (W) = 1 J/sec] A) 2.40 × 103 B) 8.64 × 103 C) 4.17 D) 2.10 × 103 E) 8.64 × 106 18. The ΔE of a system that releases 12.4 J of heat and does 4.2 J of work on the surroundings is ________ J. A) 16.6 B) 12.4 C) 4.2 D) -16.6 E) -8.2 19. Hydrogen gas and bromine gas react to form hydrogen bromide gas. How much heat (kJ) is released when 155 grams of HBr is formed in this reaction? ΔH° = -72 kJ. A) 137 B) 69 C) -69 D) -137 E) 1.12 × 105 20.The value of ΔH° for the reaction below is -126 kJ. ________ kj are released when 2.00 mol of NaOH is formed in the reaction? 2Na2O2 (s) + 2H2O (l) → 4NaOH (s) + O2 (g) A) 252 B) 63 C) 3.9 D) 7.8 E) -126 21. The molar heat capacity of an unknown substance is 92.1 J/mol-K. If the unknown has a molar mass of 118 g/mol, what is the specific heat (J/g-K) of this substance? A) 1.28 B) -92.1 C) 1.09 × 104 D) 0.781 E) 92.1 22. The specific heat capacity of lead is 0.13 J/g-K. How much heat (in J) is required to raise the temperature of of lead from 22 °C to 37 °C? A) 2.0 J B) -0.13 J C) 5.8 × 10-4 J D) 29 J E) 0.13 J 23. Given the following reactions Fe2O3 (s) + 3CO (s) → 2Fe (s) + 3CO2 (g) ΔH = -28.0 kJ 3Fe (s) + 4CO2(s) → 4CO (g) + Fe3O4(s) ΔH = +12.5 kJ the enthalpy of the reaction of Fe2O3 with CO 3Fe2O3 (s) + CO (g) → CO2 (g) + 2Fe3O4 (s) is ________ kJ. A) -59.0 B) 40.5 C) -15.5 D) -109 E) +109 24. Given the data in the table below, ΔH°rxn for the reaction 4NH3 (g) + 5O2 (g) → 4NO (g) + 6H2O (l) is ________ kJ. A) -1172 B) -150 C) -1540 D) -1892 E) The ΔH°f of O2 (g) is needed for the calculation.