Chapter 6- Thermochemistry.doc

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Chemistry
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CHEM 1320
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Dr.Tanner

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Chapter 6: Thermochemistry 1. Radiant energy is A) the energy stored within the structural units of chemical substances. B) the energy associated with the random motion of atoms and molecules. C) solar energy, i.e. energy that comes from the sun. D) energy available by virtue of an object's position. Ans: C Category: Easy Section: 6.1 6. An endothermic reaction causes the surroundings to A) warm up. D) decrease in temperature. B) become acidic. E) release CO2. C) condense. Ans: D Category: Easy Section: 6.2 7. An exothermic reaction causes the surroundings to A) increase in temperature D) decrease in temperature. B) become acidic. E) release CO2. C) expand. Ans: A Category: Easy Section: 6.2 10. Calculate the amount of heat necessary to raise the temperature of 135.0 g of water from 50.4°F to 85.0°F. The specific heat of water = 4.184 J/g·°C. A) 1.1 kJ B) 10.9 kJ C) 16.6 kJ D) 19.5 kJ E) 48.0 kJ Ans: B Category: Medium Section: 6.5 12. Three separate 3.5g blocks of Al, Cu, and Fe at 25 °C each absorb 0.505 kJ of heat. Which block reaches the highest temperature? The specific heats of Al, Cu, and Fe are 0.900 J/g·°C, 0.385J/g·°C, and 0.444 J/g·°C, respectively. A) Al B) Cu C) Fe D) Al and Cu E) Fe and Cu Ans: B Category: Easy Section: 6.5 19. Suppose a 50.0 g block of silver (specific heat = 0.2350 J/g·°C) at 100°C is placed in contact with a 50.0 g block of iron (specific heat = 0.4494 J/g·°C) at 0°C, and the two blocks are insulated from the rest of the universe. The final temperature of the two blocks A) will be higher than 50°C. B) will be lower than 50°C. C) will be exactly 50°C. D) is unrelated to the composition of the blocks. E) cannot be predicted. Ans: B Category: Medium Section: 6.5 Page 119 Chapter 6: Thermochemistry 21. Naphthalene combustion can be used to calibrate the heat capacity of a bomb calorimeter. The heat of combustion of naphthalene is –40.1 kJ/g. When 0.8210 g of naphthalene was burned in a calorimeter containing 1,000. g of water, a temperature rise of 4.21°C was observed. What is the heat capacity of the bomb calorimeter excluding the water? A) 1.76 kJ/°C B) 3.64 kJ/°C C) 7.8 kJ/°C D) 15.3 kJ/°C E) 32.9 kJ/° Ans: B Category: Medium Section: 6.5 23. Which of the following processes is exothermic, given the following: N 2g) + 2 O (g2 → N O (l)2ΔH4 = 9.67 kJ/mol N 2g) + 2 O (g2 → 2 NO (g) ΔH2 = 67.70 kJ/mol A) 2 N 2g) + 4 O (g2 → 2 N O (l) 2 4 B) ½ N 2g) + O (g)2→ ½ N O (l) 2 4 C) N 2 4l) → N (g) 2 2 O (g) 2 D) 2 N 2g) + 4 O (g2 → 2 NO (g) + 2 O (l) 2 4 E) 2 N (g) + 4 O (g) → 4 NO (g) 2 2 2 Ans: C Category: Easy Section: 6.6 26. A 100. mL sample of 0.200 M aqueous hydrochloric acid is added to 100. mL of 0.200 M aqueous ammonia in a calorimeter whose heat capacity (excluding any water) is 480. J/K. The following reaction occurs when the two solutions are mixed. HCl(aq) + NH (a3) → NH Cl(aq4 The temperature increase is 2.34°C. Calculate ΔH per mole of HCl and NH reacted. 3 A) –154 kJ/mol D) 154 kJ/mol B) –1.96 kJ/mol E) 485 kJ/mol C) 1.96 kJ/mol Ans: A Category: Difficult Section: 6.5 31. Which of the following has a ΔH° = 0 fJ/mol? - A) CO (g2 B) O (g) C)3Cl (aq) D) NH (aq) 3 E) I 2s) Ans: E Category: Easy Section: 6.6 32. Which of the following has a ΔH° = 0 fJ/mol? A) NO(g) B) CS (l) C) Fe (aq) D) H O(l) E) N (g) 2 2 2 Ans: E Category: Easy Section: 6.6 33. When 0.560 g of Na(s) reacts with excess F (g) to form NaF(s), 13.8 kJ of heat is evolved 2 at standard-state conditions. What is the standard enthalpy of formation (ΔH°) of f NaF(s)? A) -570 kJ/mol D) 24.8 kJ/mol B) –24.8 kJ/mol E) 570 kJ/mol C) –7.8 kJ/mol Ans: A Category: Medium Section: 6.6 Page 120 Chapter 6: Thermochemistry 34. When 18.5 g of HgO(s) is decomposed to form Hg(l) and O (g), 7275 kJ of heat is absorbed at standard-state conditions. What is the standard enthalpy of formation (ΔH°) f of HgO(s)? A) –90.7 kJ/mol D) 27.9 kJ/mol B) –7.75 kJ/mol E) 143 kJ/mol C) 0.419 kJ/mol Ans: A Category: Medium Section: 6.6 40. Glycine, C 2 O5N,2is important for biological energy. The combustion reaction of glycine is given by the equation 4C H O N(s) + 9O (g) → 8CO (g) + 10H O(l) + 2N (g) ΔH° = –3857 kJ/mol 2 5 2 2 2 2 2 rxn Given that ΔH°[Cf (g)2 = –393.5 kJ/mol and ΔH°[H O(l)f =2–285.8 kJ/mol, calculate the enthalpy of formation of glycine. A) –3,178 kJ/mol D) –268.2 kJ/mol B) –964 kJ/mol E) 2,149 kJ/mol C) –537.2 kJ/mol Ans: C Category: Medium Section: 6.6 45. During volcanic eruptions, hydrogen sulfide gas is given off and oxidized by air according to the following chemical equation: 2H 2(g) + 3O (2) → 2SO (g)2+ 2H O(g)2 Calculate the standard enthalpy change for the above reaction given: 3S(s) + 2H 2(g) → 2H S(g2 + SO (g) 2 ΔH° = 146.9 kJ/mol S(s) + O (g) → SO (g) ΔH° = –296.4 kJ/mol 2 2 A) –1036.1 kJ/mol D) 443.3 kJ/mol B) –742.3 kJ/mol
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