12.1 THE ARITHMETIC OF EQUATIONS Section Review Objectives Calculate the amount of reactants required or product formed in a nonchemical process Interpret balanced chemical equations in terms of interacting moles, representative particles, masses, and gas volume at STP Vocabulary stoichiometry Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. The coefficients of a balanced chemical equation indicate 1. the relative number of 1 of reactants and products. All 2. stoichiometric calculations begin with a 2. Only 3 3. and 4 are conserved in every reaction; moles, volumes, 4. and representative particles may not be. 5. In solving stoichiometric problems, conversion factors 6. relating moles of reactants to If you assume about the volumes of gases. Part B True-False of products are used., the balanced equation also tells you Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 6 5 7. The coefficients in a balanced chemical equation can be used to form mole ratios relating reactants to products. 8. The coefficients in a balanced chemical equation tell the relative volumes of reactants and products, expressed in any suitable unit of volume. 9. To calculate the mass of a molecule in grams, you can use the molar mass and Avogadro s number. Chapter 12 Stoichiometry 289
10. Because the mass of the reactants equals the mass of the products of a reaction, the number of moles will be conserved. 11. If the ratio of molecules in the reaction 2A 2 B 2 y 2A 2 B is 2:1:2, we can predict that 4 molecules of A 2 react with 2 molecules B 2 to produce 4 molecules of A 2 B. 12. One mole of any gas occupies a volume of 22.4 L. Part C Matching Match each description in Column B to the correct term in Column A. 13. 14. 15. 16. 17. Column A stoichiometry product coefficient 6.02 10 23 0 C, 101.3 kpa Column B a. Avogadro s number b. the calculations of quantities in chemical reactions c. STP d. a substance formed in a chemical reaction e. gives the relative number of molecules involved in a reaction Part D Questions and Problems Answer the following in the space provided. Show your work. 18. Interpret the following equation using moles, molecules, and volumes (assume STP). Compare the mass of the reactants to the mass of the product. 2N 2 (g) 3O 2 (g) y 2N 2 O 3 (g) 19. How many moles of chlorine gas will be required to react with sufficient iron to produce 14 moles of iron(iii) chloride? 2Fe(s) 3Cl 2 (g) y 2FeCl 3 (g) 290 Core Teaching Resources
12.2 CHEMICAL CALCULATIONS Section Review Objectives Construct mole ratios from balanced chemical equations and apply these ratios in mole-mole stoichiometric calculations Calculate stoichiometric quantities from balanced chemical equations, using units of moles, mass, representative particles, and volumes of gases at STP Key Equations mole-mole relationship used in every stoichiometric calculation: ag uy bw (given quantity) (wanted quantity) x mol G b mol W x b mol W a mol G a Given Mole Ratio Calculated Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. Mole ratios from balanced equations may be used to solve 1. problems with other units such as numbers of 1 and 2 2. of gases at STP. The 3 from the balanced equation are used 3. to write conversion factors called 4. These conversion factors 4. are used to calculate the numbers of moles of 5 from a given 5. number of moles of 6. In mass-mass calculations, the molar 6. mass is used to convert mass to 7. 7. Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 8. In mass-mass calculations, the molar mass is used to convert mass to moles. 9. The mole ratio 2 mol HF/1 mol SnF 2 can be used to determine the mass of SnF 2 produced according to the equation: Sn(s) 2HF(g) y SnF 2 (s) H 2 (g) Chapter 12 Stoichiometry 291
10. In a volume-volume problem, the 22.4 L/mol factors always cancel out. 11. In stoichiometric problems, volume is expressed in terms of liters. 12. For a mass-mole problem, the first conversion from mass to moles is skipped. 13. For a mass-mass problem, the first conversion is from moles to mass. 14. Because mole ratios from balanced equations are exact numbers, they do not enter into the determination of significant figures. Part C Matching Match each conversion problem in Column A to the correct solution in Column B. Column A Column B 15. moles O 2 y grams O 2 mol a. molecules 1 8.0 g 6.02 10 23 molecules mol 16. liters SO 2 y grams SO 2 at STP mol b. liters 6 4.1 g 2 2.4 L mol 17. molecules He y liters He(g) at STP c. mol 3 2.0 g mol 18. grams Sn y molecules Sn mol d. molecules 2 2.4 L 6.02 10 23 molecules mol 19. molecules H 2 O y grams H 2 O mol 6.02 10 23 molecules e. grams 1 19 g mol Part D Questions and Problems Answer the following questions in the space provided. 20. How many liters of carbon monoxide (at STP) are needed to react with 4.8 g of oxygen gas to produce carbon dioxide? 2CO(g) O 2 (g) y 2CO 2 (g) 21. What mass of ammonia, NH 3, is necessary to react with 2.1 10 24 molecules of oxygen in the following reaction? 4NH 3 (g) 7O 2 (g) y 6H 2 O(g) 4NO 2 (g) 292 Core Teaching Resources
12.3 LIMITING REAGENT AND PERCENT YIELD Section Review Objectives Identify and use the limiting reagent in a reaction to calculate the maximum amount of product(s) produced and the amount of excess reagent Calculate theoretical yield, actual yield, or percent yield given the appropriate information Vocabulary limiting reagent excess reagent theoretical yield actual yield percent yield Key Equations actual yield percent yield 100 the oretical yield Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. Whenever quantities of two or more reactants are given in a 1. stoichiometric problem, you must identify the 1. This is the 2. reagent that is completely 2 in the reaction. The amount of 3. limiting reagent determines the amount of 3 that is formed. 4. When an equation is used to calculate the amount of product 5. that will form during a reaction, the value obtained is the 4. 6. This is the 5 amount of product that could be formed from a given amount of reactant. The amount of product that forms when the reaction is carried out in the laboratory is called the 6. Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 7. Normally, the actual yield in a chemical reaction will be equal to or less than the theoretical yield. 8. The actual yield of a chemical reaction can be calculated using mole ratios. Chapter 12 Stoichiometry 293
9. The amount of product can be determined from the amount of excess reagent. 10. The percent yield of a product is 100 percent. 11. If you had 100 steering wheels, 360 tires, and enough of every other part needed to assemble a car, the limiting reagent would be tires. 12. The theoretical yield is the maximum amount of product that could be formed in a chemical reaction. Part C Matching Match each description in Column B to the correct term in Column A. 13. 14. 15. 16. Column A actual yield limiting reagent theoretical yield percent yield Column B a. the ratio of the actual yield to the theoretical yield 100 b. the amount of product actually formed when a reaction is carried out in the laboratory c. the reactant that determines the amount of product that can be formed in a reaction d. the reactant that is not completely used up in a chemical reaction 17. excess reagent Part D Questions and Problems e. the maximum amount of product that can be formed during a reaction Answer the following in the space provided. 18. a. What is the limiting reagent when 3.1 mol of SO 2 react with 2.7 mol of O 2 according to the equation: 2SO 2 (g) O 2 (g) y 2SO 3 (g) b. Calculate the maximum amount of product that can be formed and the amount of unreacted excess reagent. 294 Core Teaching Resources
12 STOICHIOMETRY Practice Problems In your notebook, solve the following problems. SECTION 12.1 THE ARITHMETIC OF EQUATIONS Use the 3-step problem-solving approach you learned in Chapter 1. 1. An apple pie needs 10 large apples, 2 crusts (top and bottom), and 1 tablespoon of cinnamon. Write a balanced equation that fits this situation. How many apples are needed to make 25 pies? 2. Two moles of potassium chloride and three moles of oxygen are produced from the decomposition of two moles of potassium chlorate, KClO 3 (s). Write the balanced equation. How many moles of oxygen are produced from 12 moles of potassium chlorate? 3. Using the equation from problem 2, how many moles of oxygen are produced from 14 moles of potassium chlorate? 4. Two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. How many molecules of water are produced from 2.0 10 23 molecules of oxygen? How many moles of water are produced from 22.5 moles of oxygen? SECTION 12.2 CHEMICAL CALCULATIONS 1. Calculate the number of moles of hydrogen chloride produced from 10 moles of hydrogen. H 2 (g) Cl 2 (g) y 2HCl(g) 2. Calculate the number of moles of chlorine needed to form 14 moles of iron(iii) chloride. 2Fe(s) 3Cl 2 (g) y 2FeCl 3 (s) 3. Calculate the number of grams of nitrogen dioxide that are produced from 4 moles of nitric oxide. 2NO(g) O 2 (g) y 2NO 2 (g) 4. Calculate the mass of oxygen produced from the decomposition of 75.0 g of potassium chlorate. 2KClO 3 (s) y 2KCl(s) 3O 2 (g) 5. Calculate the mass of silver needed to react with chlorine to produce 84 g of silver chloride. (Hint: Write a balanced equation first.) 6. How many liters of carbon monoxide at STP are needed to react with 4.80 g of oxygen gas to produce carbon dioxide? 2CO(g) O 2 (g) y 2CO 2 (g) 7. Calculate the number of liters of oxygen gas needed to produce 15.0 liters of dinitrogen trioxide. Assume all gases are at the same conditions of temperature and pressure. 2N 2 (g) 3O 2 (g) y 2N 2 O 3 (g) Chapter 12 Stoichiometry 295
8. A volume of 7.5 L of hydrogen gas at STP was produced from the single-replacement reaction of zinc with nitric acid. Calculate the mass of zinc needed for this reaction. SECTION 12.3 LIMITING REAGENT AND PERCENT YIELD 1. How many moles of water can be made from 4 moles of oxygen gas and 16 moles of hydrogen gas? What is the limiting reagent? 2. Calculate the mass of water produced from the reaction of 24.0 g of H 2 and 160.0 g of O 2. What is the limiting reagent? 3. The burning of 18.0 g of carbon produces 55.0 g of carbon dioxide. What is the theoretical yield of CO 2? Calculate the percent yield of CO 2. 4. Calculate the percent yield of Cl 2 (g) in the electrolytic decomposition of hydrogen chloride if 25.8 g of HCl produces 13.6 g of chlorine gas. 5. One method for reclaiming silver metal from silver chloride results in a 94.6% yield. Calculate the actual mass of silver that can be produced in this reaction if 100.0 g of silver chloride is converted to silver metal. 2AgCl(s) y 2Ag(s) Cl 2 (g) 6. What is the actual amount of magnesium oxide produced when excess carbon dioxide reacts with 42.8 g of magnesium metal? The percent yield of MgO(s)for this reaction is 81.7%. 2Mg(s) CO 2 (g) y 2MgO(s) C(s) 296 Core Teaching Resources
12 INTERPRETING GRAPHICS Use with Section 12.3 Preparation of Salicylic Acid Student #1 mass of flask 37.820 g flask C 7 H 6 O 3 39.961 g volume of C 4 H 6 O 3 5.0 ml mass of watch glass 22.744 g Student #2 watch glass C 9 H 8 O 4 mass of flask 24.489 g 37.979 g flask C 7 H 6 O 3 40.010 g volume of C 4 H 6 O 3 5.0 ml mass of watch glass 21.688 g watch glass C 9 H 8 O 4 Two students prepared aspirin according to the following reaction in which acetic anhydride, C 4 H 6 O 3, reacts with salicylic acid, C 7 H 6 O 3, to form aspirin, C 9 H 8 O 4, and acetic acid, C 2 H 4 O 2. C 7 H 6 O 3 C 4 H 6 O 3 y C 9 H 8 O 4 C 2 H 4 O 2 The procedure involved heating the reaction mixture in a water bath for 15 minutes at 75 C, not to exceed 80 C. The mixture was removed from the water bath, and distilled water was added to decompose any unreacted acetic anhydride. The mixture was then placed in an ice bath for 5 minutes to facilitate the formation of aspirin crystals. The aspirin crystals were collected using filtration. The aspirin crystals were dried and then transferred to a watch glass and massed. Because their grades were partially based on accuracy, both students used their very best lab technique. Which student got the better grade and why? 1. Determine the molar masses of the following: a. acetic anhydride, C 4 H 6 O 3 24.197 g b. salicylic acid, C 7 H 6 O 3 c. aspirin, C 9 H 8 O 4 Chapter 12 Stoichiometry 297
2. How many moles of salicylic acid were added to the reaction mixture? Student 1 Student 2 3. Given the density of acetic anhydride to be 1.05 g/ml, what was the mass of the acetic anhydride added to the reaction? How many moles of acetic acid were added? Student 1 Student 2 4. According to the mole ratios in the given reaction, what is the limiting reagent in this reaction? 5. What is the theoretical yield, in grams, of aspirin in each reaction? Student 1 Student 2 6. What was the actual yield, in grams, of aspirin in each reaction? Student 1 Student 2 7. What was the percent yield in each reaction? Student 1 Student 2 8. Evaluate your answers. Which student got the better grade and why? 298 Core Teaching Resources
12 STOICHIOMETRY Vocabulary Review Match the correct vocabulary term to each numbered statement. Write the letter of the correct term on the line. Column A Column B 1. 2. 3. 4. 5. the starting materials in a chemical reaction a conversion factor derived from the coefficients of a balanced chemical equation interpreted in terms of moles the maximum amount of product that could be formed in a reaction the amount of a substance that contains 6.02 10 23 representative particles of that substance the substance completely used up in a chemical reaction a. mole b. stoichiometry c. mass-mass calculation d. reactants e. excess reagent 6. 7. 8. 9. 10. the ratio of how much product is produced compared to how much is expected, expressed as a percentage the calculations of quantities in a chemical reaction the actual amount of product in a chemical reaction the substance left over after a reaction takes place a stoichiometric computation in which the mass of products is determined from the given mass of reactants f. theoretical yield g. limiting reagent h. quantity i. actual yield j. percent yield Chapter 12 Stoichiometry 299
12 STOICHIOMETRY Chapter Quiz Fill in the word(s) that will make each statement true. 1. The 1 in a balanced chemical equation also reveal the 1. mole ratios of the substances involved. 2. The number of moles of a product can be calculated from a 2. given number of moles of 2. 3. In mass-mass calculations, the molar mass is used to 3. convert mass to 3. 4. In addition to mass, the only quantity conserved in every 4. chemical reaction is 4. 5. According to the equation: 5. 2NO(g) O 2 (g) y 2NO 2 (g), 22.4 L of O 2 will react with 5 L of NO at STP. 12.1 12.1 12.2 12.2 12.2 Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 6. The excess reagent determines the amount of product formed in a 12.3 reaction. 7. In the reaction 2CO(g) O 2 (g) y 2CO 2 (g), using 4 moles of CO to 12.3 react with 1 mole of O 2 will result in the production of 4 moles of CO 2. 8. To calculate the percent yield of a reaction, you use the following relationship: 12.3 the oretical yield 100 actual yield 9. The total mass of the excess reagent and the limiting reagent is equal 12.3 to the total mass of the products. 10. The actual yield is equal to the theoretical yield. 12.3 300 Core Teaching Resources
12 STOICHIOMETRY Chapter Test A A. Matching Match each description in Column B with the correct term in Column A. Write the letter of the correct description on the line. 1. 2. 3. 4. 5. 6. Column A actual yield limiting reagent theoretical yield stoichiometry percent yield excess reagent Column B a. the ratio of the actual yield to the theoretical yield, expressed as a percentage b. the amount of product formed when a reaction is carried out in the laboratory c. the reactant that determines the amount of product that can be formed in a reaction d. the reactant that is not completely used up in a reaction e. the calculated amount of product that might be formed during a reaction f. the calculation of quantities in chemical equations B. Multiple Choice Choose the best answer and write its letter on the line. 7. Which of these expressions is an incorrect interpretation of the balanced equation? 2S(s) 3O 2 (g) y 2SO 3 (g) a. 2 atoms S 3 molecules O 2 y 2 molecules SO 3 b. 2 g S 3 g O 2 y 2 g SO 3 c. 2 mol S 3 mol O 2 y 2 mol SO 3 d. none of the above 8. In a chemical reaction, the mass of the products a. is less than the mass of the reactants. b. is greater than the mass of the reactants. c. is equal to the mass of the reactants. d. has no relationship to the mass of the reactants. 9. How many liters of oxygen are required to react completely with 1.2 liters of hydrogen to form water? 2H 2 (g) O 2 (g) y 2H 2 (g) a. 1.2 L c. 2.4 L b. 0.6 L d. 4.8 L Chapter 12 Stoichiometry 301
10. How many molecules of NO 2 are produced when 2.0 10 20 molecules of N 2 O 4 are decomposed according to the following equation? N 2 O 4 (g) y 2NO 2 (g) a. 4 c. 2.0 10 20 b. 1.0 10 20 d. 4.0 10 20 11. How many liters of CO(g) at STP are produced when 68.0 g of CaCO 3 (s) is heated according to the following equation? CaCO 3 (s) y CaO(s) CO 2 (g) a. 0.679 L c. 68.0 L b. 15.2 L d. 30.4 L 12. A reaction that has been calculated to produce 60.0 g of CuCl 2 actually produces 50.0 g of CuCl 2. What is the percent yield? a. 0.833% c. 83.3% b. 96.1% d. 120% 13. When 0.2 mol of calcium is mixed with 880 g of water, 4.48 L of hydrogen gas forms (at STP). How would the amount of hydrogen produced change if the mass of water were decreased to 220 g? a. Only one half of the volume of hydrogen would be produced. b. The volume of hydrogen produced would be the same. c. The volume of hydrogen produced would double. d. No hydrogen would be produced. 14. The equation for the complete combustion of methane is CH 4 (g) 2O 2 (g) y CO 2 (g) 2H 2 O(l) To calculate the number of grams of CO 2 produced by the reaction of 29.5 g of CH 4 with O 2, the first conversion factor to use is 1 molch4 a. c. 1 6.0 g CH4 1 6.0 g CH4 1 molch4 2 mol O2 b. d. 2 9.5 g CH4 1 mol CO 2 molco 2 15. In any chemical reaction, the quantities that are conserved are a. the number of moles and the volumes. b. the number of molecules and the volumes. c. mass and number of atoms. d. mass and moles. Questions 16, 17, and 18 refer to the following equation: 3Cu(s) 8HNO 3 (aq) y 3Cu(NO 3 ) 2 (s) 2NO(g) 4H 2 O(l) 16. Calculate the number of moles of water produced when 3.3 mol of Cu(NO 3 ) 2 are formed in the reaction. a. 4.4 mol c. 4.9 mol b. 6.6 mol d. 8.8 mol 17. How many grams of Cu would be needed to react with 2.0 mol HNO 3? a. 95.3 g c. 47.6 g b. 63.5 g d. 1.50 g 2 302 Core Teaching Resources
18. If you could drop 12 atoms of copper into a beaker containing nitric acid, how many molecules of NO would be produced? a. 2 c. 8 b. 4 d. 12 C. Problems Solve the following problems in the space provided. Show your work. 19. What is the limiting reagent when 49.84 g of nitrogen react with 10.7 g of hydrogen according to this balanced equation? N 2 (g) 3H 2 (g) y 2NH 3 (g) 20. How many grams of CO are needed to react with an excess of Fe 2 O 3 to produce 558 g Fe? The equation for the reaction is: Fe 2 O 3 (s) 3CO(g) y 3CO 2 (g) 2Fe(s) 21. How many grams of butane (C 4 H 10 ) must be burned in an excess of O 2 to produce 15.0 g of CO 2? 2C 4 H 10 (g) 13O 2 (g) y 8CO 2 (g) 10H 2 O(g) 22. a. If 4.0 g of H 2 are made to react with excess CO, how many grams of CH 3 OH can theoretically be produced according to the following equation? CO(g) 2H 2 (g) y CH 3 OH(l) b. If 28.0 g of CH 3 OH are actually produced, what is the percent yield? Chapter 12 Stoichiometry 303
D. Essay Write a short essay for the following. 23. What is the importance of the coefficients in a balanced chemical equation? E. Additional Problems Solve the following problems in the space provided. Show your work. 24. A 5.00 10 2 g sample of Al 2 (SO 4 ) 3 is made to react with 450 g of Ca(OH) 2. A total of 596 g of CaSO 4 is produced. The balanced equation is: Al 2 (SO 4 ) 3 (aq) 3Ca(OH) 2 (aq) y 2Al(OH) 3 (s) 3CaSO 4 (s) a. What is the limiting reagent in this reaction? b. How many moles of excess reagent are unreacted? 25. How many liters of O 2 are needed to react completely with 10.0 L of H 2 S at STP according to the following reaction? 2H 2 S(g) 3O 2 (g) y 2SO 2 (g) 2H 2 O(g) 304 Core Teaching Resources
26. The decomposition of potassium chlorate gives oxygen gas according to the reaction: 2KClO 3 (s) y 2KCl(s) 3O 2 (g) How many grams KClO 3 are needed to produce 5.00 L of O 2 at STP? 27. Suppose that the reaction described in question 26 produces 4.80 L of O 2 in the laboratory. What is the percent yield? Chapter 12 Stoichiometry 305
12 STOICHIOMETRY Chapter Test B A. Matching Match each term in Column B with the correct description in Column A. Write the letter of the correct term on the line. 1. 2. 3. 4. 5. Column A the substance that determines the amount of product that can be formed in a reaction the amount of product that forms when a reaction is carried out in the laboratory the calculation of quantities in chemical equations the ratio of the actual yield to the theoretical yield expressed as a percent the substance that is present in enough quantity to react with a limiting reagent Column B a. percent yield b. limiting reagent c. theoretical yield d. stoichiometry e. actual yield 6. B. Multiple Choice Choose the best answer and write its letter on the line. the maximum amount of products that could be formed from given amounts of reactants 7. In a chemical reaction a. mass is conserved. c. moles are conserved. b. atoms are conserved. d. both mass and atoms are conserved. 8. Which of the following is a correct interpretation of this balanced equation? 2Al(s) 3Pb(NO 3 ) 2 (aq) y 2Al(NO 3 ) 3 (aq) 3Pb(s) a. 2 atoms Al 3 molecules Pb(NO 3 ) 2 y 2 molecules Al(NO 3 ) 3 3 atoms of Pb b. 2 grams Al 3 grams Pb(NO 3 ) 2 y 2 grams Al(NO 3 ) 3 3 grams Pb c. 2 moles Al 3 moles Pb(NO 3 ) 2 y 2 moles Al(NO 3 ) 3 3 moles Pb d. both a and c 9. If 3.0 moles of HCl are consumed in the reaction below, how many moles of FeCl 3 are produced? 6HCl Fe 2 O 3 y 2FeCl 3 3H 2 O a. 0.50 mol c. 2.0 mol b. 1.0 mol d. 4.0 mol f. excess reagent 306 Core Teaching Resources
10. Given the equation 2H 2 O y 2H 2 O 2, how many moles of H 2 O would be required to produce 2.5 moles of O 2? a. 2.0 mol c. 4.0 mol b. 2.5 mol d. 5.0 mol 11. If 3.00 mol of CaCO 3 undergo decomposition to form CaO and CO 2, how many grams of CO 2 are produced? a. 3.00 g c. 88.0 g b. 44.0 g d. 132 g 12. If CuO H 2 y Cu H 2 O, how many moles of H 2 O are produced when 240 grams of CuO react? a. 1.0 mol c. 18 mol b. 3.0 mol d. 54 mol 13. Given the balanced equation 16HCl 2KMnO 4 y 2KCl 2MnCl 2 5Cl 2 8H 2 O, if 1.0 mol of KMnO 4 reacts, how many moles of H 2 O are produced? a. 0.50 mol c. 4.0 mol b. 2.0 mol d. 8.0 mol 14. Based on the equation in question 13, how many grams of KCl are produced when 1.0 mol of KMnO 4 reacts? a. 1.0 g c. 150 g b. 75 g d. 158 g 15. If 110 grams of HCl are used in the reaction 6HCl Fe 2 O 3 y 2FeCl 3 3H 2 O, how many moles of FeCl 3 are produced? a. 1.0 mol c. 3.0 mol b. 2.0 mol d. 6.0 mol 16. In the reaction Zn H 2 SO 4 y ZnSO 4 H 2, how many grams of H 2 SO 4 are required to produce 1.0 gram of H 2? a. 1.0 g c. 49 g b. 2.0 g d. 98 g 17. If 18 grams of carbon react with oxygen to produce carbon dioxide, how many molecules of oxygen would be required? a. 1.5 molecules c. 9.0 10 23 molecules b. 48 molecules d. 3.2 10 24 molecules 18. Given the reaction 2NO(g) O 2 (g) y 2NO 2 (g), if 6.5 L of O 2 react at STP, how many liters of NO 2 are produced? a. 6.5 L c. 26 L b. 3.2 L d. 13 L 19. Given the reaction Zn 2HCl y ZnCl 2 H 2, if 2.0 mol Zn and 5.0 mol HCl are allowed to react a. Zn is the limiting reagent. c. 1.0 mol of ZnCl 2 is produced. b. HCl is the limiting reagent. d. 5.0 mol of H 2 is produced. Chapter 12 Stoichiometry 307
20. Once the reaction in question 19 is completed, how many moles of excess reactant remain? a. 3.0 mol c. 4.0 mol b. 1.0 mol d. 2.0 mol 21. Given the reaction CaCO 3 (s) y CaO(s) CO 2 (g), if 50.0 g of CaCO 3 react to produce 20.0 g of CO 2, what is the percent yield of CO 2? a. 66.7% c. 90.9% b. 40.0% d. 250% C. Problems Solve the following problems in the space provided. Show your work. 22. Ammonia, NH 3, is a typical ingredient in household cleaners. It is produced through a combination reaction involving N 2 (g) and H 2 (g). If 12.0 mol of H 2 (g) react with excess N 2 (g), how many moles of ammonia are produced? 23. The compound tin(ii) fluoride, or stannous fluoride, once was a common ingredient in toothpaste. It is produced according to the following reaction: Sn(s) 2HF(g) y SnF 2 (s) H 2 (g) If 45.0 grams of HF react with Sn, how many grams of stannous fluoride are produced? 24. The combustion of methane, CH 4 (g), can be described by the following equation: CH 4 (g) 2O 2 (g) y CO 2 (g) 2H 2 O(g) If 150 moles of carbon dioxide are produced, what mass, in grams, of methane is required? 308 Core Teaching Resources
25. If aluminum reacts with oxygen according to the following equation: 4Al(s) 3O 2 (g) y 2Al 2 O 3 (s) what mass, in grams, of the product would be produced if 625 ml of oxygen react at STP? 26. Given the following reaction: CaCO 3 (s) y CaO(s) + CO 2 (g), if 50.8 grams of CaCO 3 react to produce 26.4 grams of CaO, what is the percent yield of CaO? D. Essay Write a short essay for the following. 27. Based on the following general reaction, if 1.0 mole of A is allowed to react with 2.0 moles of B, which reactant is the limiting reactant and what amount of A 2 B 3 can be produced? 2A 3B y A 2 B 3 Chapter 12 Stoichiometry 309
E. Additional Problems Solve the following problems in the space provided. Show your work. 28. In photosynthesis, plants use energy from the sun in combination with carbon dioxide and water to form glucose (C 6 H 12 O 6 ) and oxygen. If 4.50 moles of water react with carbon dioxide, what mass of glucose is produced? 29. Acetylene gas (C 2 H 2 ) is used in welding and produces an extremely hot flame according to the reaction: 2C 2 H 2 (g) 5O 2 (g) y 4CO 2 (g) 2H 2 O(g) If 5.00 10 4 g of acetylene burn completely, how many grams of carbon dioxide are produced? 30. Given the following reaction: 3H 2 SO 4 (aq) Ca 3 (PO 4 ) 2 (s) y 3CaSO 4 (s) 2H 3 PO 4 (aq), if 1.25 10 5 kg of H 2 S) 4 react, how many kilograms of H 3 PO 4 are produced? 31. Ammonia and copper(ii) oxide react according to the following: 2NH 3 (g) 3CuO(s) y N 2 (g) 3Cu(s) 3H 2 O(g) If 57.0 g of ammonia are combined with 290.0 g of copper(ii) oxide: a. Identify the limiting reactant. b. How much of the excess reactant remains, in moles? c. What mass of nitrogen gas is produced, in grams? 32. If ammonia reacts according to the following equation, how many kilograms of NO could be produced from 10.0 kg of NH 3 if the percent yield of NO is 80.0%? 4NH 3 (g) 5O 2 (g) y 4NO(g) 6H 2 O(g) 310 Core Teaching Resources