4. During respiration, glucose reacts with oxygen gas to produce carbon dioxide and water. Write a balanced equation:

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1 Name: Date: Unit 7B - Stoichiometry Accelerated Chemistry I Mole Ratios 1. This balanced equation shows reaction of carbon monoxide reacts with oxygen gas: 2CO(g) + O 2 (g) 2CO 2 (g) a. What is the ratio of moles of CO 2 produced for every mole of O 2 consumed? Write this as a conversion factor: Answ: 2 mol CO 2 : 1 mol O 2 b. How many moles of CO 2 are produced when 5 moles of O 2 are consumed? Write this out, showing your work: Answ: 10 mol CO 2 c. Does the number of moles of gas present increase, decrease, or remain constant when this reaction occurs? 2. Write a balanced equation for the reaction of magnesium with hydrochloric acid. How many moles of Mg are required to react with 2.0 moles of HCl? Answ: 1.0 mol Mg 3. Write a balanced equation for reaction of hydrochloric acid with aluminum. How many moles of HCl are required to react with 0.87 moles of aluminum? Answ: 2.6 mol HCl 4. During respiration, glucose reacts with oxygen gas to produce carbon dioxide and water. Write a balanced equation: a. How many moles of oxygen gas are required to react with 0.25 mol of glucose? Answ: 1.5 mol O 2 b. How many moles of carbon dioxide would be produced from 0.25 mol of glucose? Answ: 1.5 mol CO 2 5. Zinc reacts with aqueous sulfuric acid to produce a soluble ionic compound and a gas. How many moles of gas can be produced from 0.36 mol of zinc? Answ: 0.36 mol H 2 Unit 7B Student Handout 1

2 Mass-Mass Conversions Use your graphic organizer as a guide to solve the following problems. 6. Balance this equation: Cr(s) + S 8 (s) Cr 2 S 3 (s) How many grams of Cr 2 S 3 are produced when this reaction proceeds with 10.0 g of Cr being consumed? Answ: 19.3 g Cr 2 S 3 7. Balance this equation: CS 2 (l) + NH 3 (g) H 2 S(g) + NH 4 SCN(s) How many grams of hydrogen sulfide are produced when g of carbon disulfide are consumed? Answ: g H 2 S 8. a. Write and balance the following equation: Iron (III) sulfide reacts with hydrochloric acid to produce iron (III) chloride and gaseous dihydrogen sulfide b. How many grams of iron(iii) chloride are produced when 26 grams of dihydrogen sulfide gas are produced in this reaction? Answ: 82 g FeCl 3 9. Nitrogen gas combines with hydrogen gas to form ammonia. How many grams of ammonia are formed when 145 g nitrogen gas are consumed by hydrogen? Answ: 176 g 10. How many grams of water vapor are produced from the combustion of 74.6 g of methane? Answ: 168 g Unit 7B Student Handout 2

3 11. Zinc reacts with copper (II) chloride in a single replacement reaction. a. How many grams of zinc would be needed to produce g of copper? Answ: g Zn b. How many grams of copper (II) chloride are needed to produce g zinc chloride? Answ: g c. If g of zinc chloride are produced in this reaction, how many grams of copper are produced at the same time? Answ: g Cu 12. Phosphorus (P 4 ) combusts to produce an oxide with phosphorus in the +5 oxidation state and a molar mass of 284 g/mol. a. How many grams of product would be produced from 50.0 g phosphorus? Answ: 115 g b. How many grams of oxygen gas would be needed in part a.? Answ: 64.6 g c. If g of product are needed, how many grams of the reactant phosphorus are required? Answ: g 13. Determine the mass of magnesium hydroxide produced when g magnesium nitride reacts with water. (Ammonia is the other product.) Answ: g 14. Determine the mass of carbon dioxide produced when g propane is combusted. Answ: 2.56 g Unit 7B Student Handout 3

4 15. Nickel can react with gaseous carbon monoxide to form Ni(CO) 4. Other metals present do not react. If 94.2 g of a mixture of metals reacts with carbon monoxide to produce 98.4 g Ni(CO) 4, what is the mass percent of nickel in the original sample? Answ: 33.8 g Ni = 35.9 % by mass 16. A g sample of iron reacts with element Q to form g Fe 2 Q 3. Determine the identity of element Q. (Fe=55.85 g/mol) Answ: Q = oxygen 17. When a certain element whose formula is X 4 combines with HCl, the results are XCl 3 and hydrogen gas. Write a balanced equation for the reaction. When 24.0 g of hydrogen gas results from such a reaction, 248 g of X 4 are consumed. Identify element X. Answ: P 18. Problem Using Molarity: If aluminum reacts 2.50 L of hydrochloric acid to produce 10.2 g of gas. What was the concentration of the hydrochloric acid? Answ: 4.04 M HCl Unit 7B Student Handout 4

5 19. How many milliliters of M Na 2 CO 3 are necessary to completely react with 27.2 ml of M HNO 3? (Carbonic acid, when produced, decomposes into carbon dioxide and water.) Answ: 16.4 ml A H 2 N 2 B NH Write the balanced equation for the precipitation reaction in which aqueous potassium iodide reacts with aqueous lead (II) nitrate to produce a lead (II) precipitate. How much M potassium iodide solution (in liters) is required to completely precipitate the Pb 2+ in L of M lead nitrate? Answ: L KI Limiting Reactants 21. Consider the reaction: 2A + B C The diagram here represents the initial reaction mixture. If all the molecules of A were converted into C, how many molecules of C could you make? If all the molecules of B were converted into C, how many molecules of C could you make? Which reactant, A or B, is the limiting reagent? 22. Consider the reaction N H 2 2 NH 3. Assuming each model represents one mole of the substance, show the number of moles of the product and the excess reagent left after the complete reaction. Unit 7B Student Handout 5

6 23. Nitrogen monoxide reacts with oxygen gas to form nitrogen dioxide, a dark-brown gas: In one experiment mol of nitrogen monoxide is mixed with mole of oxygen gas. a. Calculate which of the two reactants is the limiting reagent. Answ: NO limits b. Calculate the number of moles of nitrogen dioxide produced. Answ: mol NO 2 Additional Limiting Reagent Problems 24. Write a balanced equation for reaction of zinc and iodine to form zinc iodide. a. Suppose that 50.0 g Zn and 50.0 g I 2 are used. Which element is the limiting reagent? Answ: I 2 limits b. How many grams of zinc iodide can be produced? Answ: 62.9 g c. How many grams of the excess element remain un-reacted? Answ: 37.1 g excess Zn 25. Given the balanced chemical equation: 2 CO(g) + O 2 (g) 2 CO 2 (g) calculate the mass of carbon dioxide that can be made from 30.0 g of CO and 30.0 g of O 2. Calculate the amount of excess reactant remaining. Answ: 47.1 g CO 2, 12.9 g O 2 excess Unit 7B Student Handout 6

7 26. Acetylene gas (ethyne) is commonly used in high temperature torches. a. Write a balanced equation for the reaction of acetylene with hydrogen gas to form ethane. b. How many grams of ethane can be produced from a mixture of 30.3 grams of acetylene and 4.14 grams of H 2? Answ: 30.9 g, H 2 limits c. How many grams of excess reagent remain unreacted? Answ: 3.6 g ethyne excess 27. Titanium is a strong, lightweight metal that is used in the construction of rockets, jet engines, and bicycles. It can be prepared by reacting TiCl 4 with Mg metal at very high temperatures. The products are Ti(s) and MgCl 2. a. Write a balanced equation for the reaction described. b. How many grams of Ti metal can be produced from a reaction involving g of TiCl 4 and g of Mg? Answ: 6.43x10 3 g Ti 28. The first step in the manufacturing process of phosphorus is the reaction: 2 Ca 3 (PO 4 ) 2 (s) + 6 SiO 2 (s) 6 CaSiO 3 (s) + P 4 O 10 (g) If 20.0 g of calcium phosphate (310.2 g/mol) and 20.0 g of silicon dioxide (60.1 g/mol) are reacted, how many grams of P 4 O 10 (284 g/mol) can be produced? How many grams of excess reagent remains unreacted? Answ: 9.16 g P 4 O 10, 8.4 g SiO 2 excess Unit 7B Student Handout 7

8 29. The depletion of ozone (O 3 ) in the stratosphere has been a matter of concern in recent years. It is believed that ozone can react with nitric oxide (NO) that is discharged from the high-altitude jet plane, the SST. The reaction is O 3 + NO O 2 + NO 2 a. If g of O 3 reacts with g of NO, how many grams of NO 2 would be produced? Which compound is the limiting reagent? Answ: g NO 2, O 3 limits b. Calculate the number of moles of the excess reagent remaining at the end of the reaction. Answ: mol NO excess Reaction Yield 30. Hydrogen fluoride is used in the production of aluminum metal. It is prepared by the reaction of calcium fluoride with sulfuric acid. In one process 6.00 kg of calcium fluoride are treated with an excess of sulfuric acid and yield 2.86 kg of hydrofluoric acid. Calculate the percent yield of hydrofluoric acid. Answ: 92.9 % 31. Nitroglycerin (C 3 H 5 N 3 O 9 ) is a powerful explosive. Four moles of nitroglycerin decompose to generate N 2, CO 2, H 2 O and O 2 along with a large amount of heat. A total of 29 moles of gas are produced. It is the sudden formation of these gases, together with their rapid expansion, that produces the explosion. a. Write a balanced equation for the decomposition of nitroglycerin. Unit 7B Student Handout 8

9 b. What is the maximum amount of O 2 in grams that can be obtained from g of nitroglycerin (227.1 g/mol)? Answ: 7.05 g O 2 c. Calculate the percent yield in this reaction if the amount of O 2 generated is found to be 6.55 g. Answ: 92.9% Mass-Energy Calculations The heat released or absorbed in a reaction is called ΔH rxn, the heat of reaction. For exothermic reactions, where heat is released, ΔH rxn is negative. The heat of reaction is based on the mole quantities shown in the balanced equation. For reactant or product quantities other than those in the balanced equation, convert using mole ratios. 32. How much heat will be transferred in the following reaction if 14.8moles of hydrogen reacts with excess oxygen according to the following reaction: Answ: kj 2H 2 + O 2 2H 2 O kJ IS HEAT RELEASED OR ABSORBED WHEN THE HYDROGEN REACTS? 33. Calcium carbide, CaC2, is manufactured by the reaction of calcium oxide with carbon at high temperature. What is the enthalpy change if 10.0 g of calcium oxide is allowed to react with an excess of carbon? Answ: kj Calcium oxide (s) + Carbon (s) Calcium carbide(s) + Carbon monoxide (g) H rxn = kj/mol IS THE REACTION ENDOTHERMIC OR EXOTHERMIC? Unit 7B Student Handout 9

10 34. How much heat would be released when 88.2g of iron(iii)oxide is produced from a synthesis reaction if H rxn = -826 kj/mol of Fe that reacts? Answ: kj 35. An exothermic combustion reaction with methane gas (CH 4 ) and excess oxygen has a H rxn of kj/mol of CH 4. How much energy is released if 44.2g of methane are combusted? Answ: kj 36. When H 2 O 2 decomposes H rxn = -196 kj/mol of H 2 O 2. If 587 kj of energy was released during a reaction, how many grams H 2 O 2 was decomposed? How many moles of oxygen gas was produced? Answ: 102 g H 2O 2, 1.50 mol O The combustion of ethanol (C 2 H 5 OH) is an exothermic reaction that releases kj per mole of ethanol. How many grams of carbon dioxide are created if 12,463-kJ of energy are released? Answ: g CO If the molar heat of combustion of butane is 2859 kj/mol, then how much heat is released from each gram of butane? Answ: kj/ g Unit 7B Student Handout 10

11 39. What is the heat of combustion for a candle (in cal/g) if 0.42-g of a candle burns and it causes 100.g of water in a calorimeter to increase its temperature by 26.8 o C? Answ: - 6.4x10 3 cal/g Challenge: Stoichiometry to Determine Empirical and Molecular Formulas 40. Styrene, the building block of polystyrene, consists of only C and H. If g of styrene is burned in oxygen and produces g of CO 2 and g of H 2 O, what is the empirical formula of styrene? (Hint: What elements within the produces are present in styrene? How can you work backwards from the products to the empirical formula?) Answ: CH Unit 7B Student Handout 11