Chemistry Stoichiometry and Heat Exam (ver.1) Mr. Thaler. Please do not write on this exam. Mark your answers on the scantron only.

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1 1. Identify from the unbalanced equations below the one that does not represent a redox reaction. a. H 2O 2(aq) + MnO 4 - (aq) O 2(g) + Mn 2+ (aq) b. H 2(g) + N 2(g) NH 3(g) c. NaCl (aq) + AgNO 3(aq) NaNO 3(aq) + AgCl (s) d. Cu (s) + AgNO 3(aq) Cu(NO 3) 2(aq) + Ag (s) 2. Identify the oxidizing agent in the following reaction: 2Na + 2H 2O 2NaOH + H 2 a. Na b. H 2O c. NaOH d. H 2 3. Which atom is reduced in the following unbalanced redox equation? K 2Cr 2O 7 + H 2O + S KOH + Cr 2O 3 + SO 2 a. S b. O c. Cr d. K 4. Identify the reducing agent in the following reaction: CH 4 + 2O 2 CO 2 + 2H 2O a. H 2O b. CO 2 c. O 2 d. CH 4 5. When the following redox equation is balanced, what is the coefficient on H 2O? NaOH + Ca(OH) 2 + C + ClO 2 NaClO 2 + CaCO 3 + H 2O a. 2 b. 3 c. 4 d. 5 e When the following redox equation is balanced, what is the coefficient on NO 2? NO 3 - (aq) + I 2 (s) IO 3 - (aq) + NO 2 (g) The reaction occurs in acidic solution. a. 2 b. 4 c. 6 d. 8 e How many liters of nitrogen dioxide are produced (at STP) when 9.33 g of copper metal are reacted with excess nitric acid, according to the following unbalanced redox equation? Cu (s) + HNO 3 (aq) Cu(NO 3) 3 (aq) + NO 2 (g) + H 2O (l) a L b L c L d L 8. How many L of O 2 are produced in the decomposition of 21 g H 2O 2 at STP? 2H 2O 2 O 2 + 2H 2O a. 6.9 L b. 28 L c. 14 L d. 21 L 9. How many moles of carbon-12 are there in 12 g of carbon-12? a. 1 mole c x moles b 22.4 moles d. 12 moles

2 10. Find the empirical formula of a compound that contains g of palladium and 0.80 g of hydrogen. a. Pd 2H 2 b. PdH 2 c. Pd 5H d. PdH What would be the molecular formula of the compound in the preceding question if its molar mass were g/mol? a. PdH 10 b. Pd 2H 4 c. Pd 10H 10 d. Pd 10H A compound containing only hydrogen and carbon has a molar mass of g /mol. If the compound contains g /mol of hydrogen, what is the molecular formula? a. C 2H 9 b. C 8H 19 c. C 4H 18 d. C 8H Identify the limiting reactant when 4.68 g of Fe reacts with 2.88 g of S to produce FeS. a. FeS b. Fe c. S 14. Identify the limiting reactant when 1.22 g of O 2 reacts with 1.05 g of H 2 to produce water. O 2 + 2H 2 2H 2O a. O 2 b. H 2O c. H How many grams of water are expected to be produced in the reaction described in the preceding question? a g b g c g d g 16. Referring to the preceding two questions, if 1.15 g H 2O is actually produced in the lab, what is the percent yield? a % b % c % d % 17. Determine the limiting reactant when 31.5 g of S reacts with 8.65 g of O 2 to produce SO 2. a. SO 2 b. S c. O What mass of SO 2 would be produced in the reaction in the preceding question? a g b g c g d g 19. Calculate the percent yield for the reaction between 6.92 g of K and 4.28 g of O 2 if 7.36 g of KO 2 is actually produced. a. 61.8% b. 58.2% c. 77.2% d. 94.0% 20. Determine the empirical formula of a compound containing 5.75 g sodium, 3.5 g nitrogen, and 12.0 g oxygen. a. NaNO 2 b. NaNO c. Na 2NO 3 d. NaNO If 4.1 g of Cr is heated (reacted) with 9.3 g of Cl 2, what mass of CrCl 3 will be produced? 2Cr + 3Cl 2 2CrCl 3 a g b. 13 g c. 17 g d g

3 22. A clean crucible with cover is determined to weigh g. An unknown hydrate of copper(ii) sulfate is added to the crucible, which is weighed again at g. After repeatedly heating the crucible, its contents, and cover over a Bunsen burner, allowing them to cool, and weighing them, two weights of g are obtained. From these data, determine which of the following is the closest empirical formula for the unknown hydrate. a. CuSO 4 2H 2O c. CuSO 4 4H 2O b. CuSO 4 5H 2O d. CuSO 4 7H 2O 23. Based on the percentage of water in the best possible answer to the preceding question, and the percentage of water in the measured sample (from the data), what is the percent error for the above-described investigation? a. 2% b. 3% c. 4% d. 5% 24. Determine the expected yield if 3.74 g of Na is reacted with excess O 2 to produce Na 2O 2 (molar mass = g /mol). 2Na + O 2 Na 2O 2 a. 146 g b g c g d g 25. Calculate the percent yield if 5.34 g of Na 2O 2 is recovered in the reaction described in the preceding question. a. 84.2% b. 70.0% c. 29.4% d. 14.7% 26. A 37.0-g sample of distilled water changed temperature from 99.0 o C to 25.0 o C in 14.8 minutes. How much heat (q) was transferred to the surroundings in this process? a J b. 11 J c kj d. 11 kj 27. When g of hydrogen reacts with chlorine in a calorimeter containing g of water, the temperature rises from o C to o C. Calculate q sur for the process. (Remember! T determines (1) the number of significant digits and (2) the sign of your answer.) H 2 (g) + Cl 2 (g) 2HCl (g) a kj b. _ J c J d. _ 8.87 kj 28. What is q rxn for the process in the preceding question? a. _ J b. _ 8.87 kj c J d kj 29. Calculate H in kj (per mol of hydrogen or chlorine, or per two mol of HCl (g)) for the process in preceding two questions. a kj b. _ 17.8 kj c. _ 8.89 kj d kj 30. A 4.11-g sample of silicon (Si) is heated with 11.1 J of energy and the temperature changes from 15.0 o C to 18.8 o C. What is the specific heat of Si based on this? a J /g. o C b. 10. J /g. o C c J /g. o C d J /g. o C 31. What is the specific heat of silver if the temperature of a 15.4-g sample of silver is increased by 11.2 o C when 40.5 J of heat is added? a g /J. o C b J /g. o C c J /g. o C d g /J. o C

4 32. Does the enthalpy diagram to the left represent an endothermic or exothermic reaction? a. endothermic b. exothermic 33. Does the reaction to the left gain or lose heat energy (at constant pressure)? a. gains b. loses 34. How much heat will be released when 6.44 g of sulfur reacts with excess oxygen according to the following equation? 2S + 3O 2 2SO 3 H o = _ kj a. _ 79.5 kj b. _ 795 kj c kj d. _ 7.95 kj 35. How much heat will be absorbed if 27.1 g of iodine reacts with excess hydrogen according to the following equation? H 2 (g) + I 2 (g) 2HI (g) H o = kj a. _ 8.9 kj b kj c kj d kj 36. From the following enthalpy changes SOCl 2 (g) + NiO (s) SO 2 (g) + NiCl 2 (s) H o = _ 150 kj and SOCl 2 (g) + H 2O (g) SO 2 (g) + 2HCl (g) H o = _ 27 kj, calculate H for the following reaction: NiO (s) + 2HCl (g) NiCl 2 (s) + H 2O (g). a. _ 123 kj b kj c kj d. _ 177 kj 37. From the following enthalpy changes 2Al (s) + 3 / 2O 2 (g) Al 2O 3 (s) H o = _ 1601 kj and 2Fe (s) + 3 / 2O 2 (g) Fe 2O 3 (s) H o = _ 821 kj, calculate for the following reaction: 2Al (s) + Fe 2O 3 (s) 2Fe (s) + Al 2O 3 (s). a. _ 780 kj b. _ 2422 kj c kj d kj

5 NH 4 + (aq) + NO 3 - (aq) Refer to the enthalpy diagram to the left to answer the NH 4 NO 3 (s) following five questions. 38. What would be the sign of H for the dissociation reaction, NH 4NO 3 (s) NH 4 + (aq) + NO 3 - (aq)? a. Capricorn b. Gemini c. negative d. positive 39. Would the above reaction be exothermic or endothermic? a. exothermic b. endothermic 40. What would be the sign for q surroundings? (The reaction occurs in water.) a. negative b. positive 41. Would the flask in diagram to the left be hot or cold to the touch? a. hot b. cold 42. What would be the sign of q reaction? a. negative b. positive

6 CaCl 2 (s) Ca 2+ (aq) + 2Cl (aq) H = kj/mol 43. What would be the sign of q rxn? a. negative b. positive 44. Would the flask in diagram to the left be hot or cold to the touch? a. hot b. cold 45. Which of the following statements is true regarding the enthalpy diagram to the left in reference to the equation? H = H products _ H reactants a. H products < H reactants b. H products > H reactants c. H products = H reactants d. none of the above For each of the following, mark the letter of the definition that best matches the term. 46. heat capacity 47. specific heat 48. calorimetry 49. temperature 50. heat a. measurement of the amount of heat released or absorbed by a reaction b. the total internal energy of matter that is transferred from one object of higher temperature to another of lower temperature c. heat capacity of one gram of a substance d. the average kinetic energy of atoms and molecules in a substance e. amount of heat required to raise the temperature of a substance by 1 o C