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Reaction Stoichiometry

Reaction Stoichiometry. I. Introduction to Reaction Stoichiometry A. Definitions 1. Stoichiometry - deals with the amount of reactants and products in chemical reactions 2. Mole Ratio - conversion factor that relates the number of moles of any two

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Reaction Stoichiometry

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  1. Reaction Stoichiometry

  2. I. Introduction to Reaction Stoichiometry A. Definitions 1. Stoichiometry- deals with the amount of reactants and products in chemical reactions 2. Mole Ratio - conversion factor that relates the number of moles of any two substances involved in a chemical reaction

  3. B. Types of Stoichiometry Problems (A is the given, B is the unknown) 1. mole-mole (mole A  mole B) 2. mole-mass (mole A  mass B) 3. mass-mole (mass A  mole B) 4. mass-mass (mass A  mass B)

  4. C. Diagram Ais the given B is what you need to find - the unknown *All problems will include a mole B conversion factor mole A 1 mole A # mole B molar mass B MASS A -----> MOLE A ------> MOLE B ------> MASS B molar mass A # mole A 1 mole B

  5. III. Mole Ratios and Coefficients in Equations A. 2H2 + O2 ----------> 2H2O • H2, O2 2) H2, H2O 3) O2, H2O 2 mol H2 1 mol O2 2 mol H2 2 mol H2O1mol O22 mol H2O 1 mol O2 2 mol H2 2 mol H2O 2 mol H2 2 mol H2O 1 mol O2 B. 2KClO3 ----------> 2KCl + 3O2 1) KClO3, KCl 2)KClO3 , O2 3) KCl, O2

  6. II. Solving Stoichiometry Problems (All Problems Include Mole Ratios) • Mole-Mole electricity 1. 2 Na + Cl2 ----------> 2NaCl A – Given B - find a) 4 moles of Na will react with (?) moles of Cl2? 4.0 mol Na X 1.0 mol Cl2 = 2 mol Cl2 12.0 mol Na

  7. A.Mole –Mole Problem • 2 Na + Cl2 ----------> 2NaCl A - GivenB - Find b)6 moles of Na will form (?) moles of NaCl? 6 mol Na X 2 mol NaCl = 6 mol NaCl 1 2 mol Na

  8. B. Mole-Mass 1. CaO + H2O ----------> Ca(OH)2 AB a)2 moles of CaO will produce(?)grams of Ca(OH)2 2 mol CaO x 1 mol Ca(OH)2 x 74.1g Ca(OH)2 = 1 1 mol CaO1 mol Ca(OH)2 148 g Ca(OH)2

  9. CaO + H2O ----------> Ca(OH)2 b) How many grams of CaO are needed to form 2 moles of Ca(OH)2? 2 mol Ca(OH)2 x 1 mol CaO x 56.1g CaO = 1 1 mol Ca(OH)2 1 mol CaO 112g CaO

  10. Mass-Mole 1. Zn + 2HCl ----------> ZnCl2 + 2H2 • How many moles of zinc chloride are formed when 196.2 grams of zinc react with hydrochloric acid? 196.2g Zn x 1 mol ZnCl2 = 3.001 mol ZnCl2 1 65.38g Zn

  11. 1. Zn + 2HCl ----------> ZnCl2 + 2H2 b) How many moles of zinc are necessary to form 67.70 grams of zinc chloride? 67.70g ZnCl x 1 mol ZnCl2 x 1 mol Zn = 1 136.29 g ZnCl2 1 mol ZnCl2 .4967 mol Zn

  12. D. Mass-Mass 1. CH4 + 2O2 ----------> CO2 + 2H2O • How many grams of carbon dioxide are formed when 64.0 grams of oxygen react with methane? 64.0g O2 x 1 mol O2 x 1 mol CO2 x 44.0g CO2 = 1 32.0g O22 mol O2 1 mol CO2 44.0g CO2

  13. 1. CH4 + 2O2 ----------> CO2 + 2H2O b) How many grams of methane are needed to produce 48.0 grams of water? 48.0g H2O x 1 mol H2O x 1 mol CH4 x 16.0g CH4 = 1 18.0g H2O 2 mol H2O 1 mol CH4 21.3g CH4

  14. III. Limiting Reactant A. Definitions 1. limiting reactant – limits the extent of reaction and determine the amount of product (reactant that is used up first) 2. excess reactant – portion of reactant that remains after a reaction is complete

  15. B. What are some examples that model limiting reactant and excess reactant? 1. hamburger + bun 2. cake recipe requires 2 eggs and 3 cups of flour, and 1 cup sugar

  16. C. How is the Limiting Reactant Determined? 1.Divide number of moles of each reactant by its coefficient in the balanced equation 2. The substance with the smaller number is the limiting reactant. 3. The substance with the larger number is the excess reactant.

  17. ExampleDetermine the limiting reactant, the excess reactant reactant and the number of moles of each product? (6 moles of H2 combined with 3 moles of N2) 1.3 H2(g) + N2(g)  2NH3(g) 6 mol 3 mol • 6/3 = 2 3/1 = 1 H2 is excessN2 is limiting b) 3 mol N2 x 2 mol NH3 = 6 mol NH3 1 1 mol N2

  18. Determine the limiting reactant, the excess reactant and the number of moles of each product 2. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) 2.5 mol Zn +3.5 mol HCl are combined • 2.5/1 = 2.5 3.5/2 = 1.75 Zn is excessHCl is limiting b) 3.5 mol HCl x 1 mol ZnCl2 = 1.8 mol ZnCl2 1 2 mol HCl c) 3.5 mol HCl x 1 mol H2 = 1.8 mol H2 1 2 mol HCl

  19. IV. Percent Yield • Definitions 1. theoretical yield – maximum amount of product that can be produced from a given amount of reactant 2. actual yield – amount of product actually produced during a reaction carried out in the lab 3. percent yield – ratio of actual yield to the theoretical yield expressed as a percent

  20. % Yield = Actual yield (experiment results) X 100% Theoretical yield (stoichiometric calculations) B. Procedure 1. Determine theoretical yield ( mass- mass stoichiometric calculation) 2. Divide actual yield (experiment results in grams) by theoretical yield 3. Multiply by 100% to get percent yield

  21. 1. Zinc reacts with iodine in a synthesis reaction. a. Determine the theoretical yield if 125.0g of zinc is used. b. Determine the % yield if the mass of the product zinc iodide recovered is 556g. Zn(s) + I2(s)  ZnI2(s) a)125.0g Zn x 1 mol Zn x 1 mol ZnI2 x 329.2g ZnI2 = 707.4g 1 65.4g Zn 1 mol Zn 1 mol Zn Theoretical Yield is 707.4 g ZnI2 b) Actual yield…………..556 = 78.6%(percent yield) Theoretical yield…….707.4

  22. 2. Water decomposes when subject to an electric current to form hydrogen gas and oxygen gas. In the lab, 60.0 g of oxygen is recovered when 72.0g of water is decomposed. What is the theoretical yield? What is the percent yield? electricity 2 H2O  2H2 + O2 72.0g H2O x 1 mol H2O x 1 mol O2 x 32.0g O2 = 64.0g O2 1 18.0g H2O 2 mol H2O 1 mol O2 Actual Yield…………60.0g = 93.8%(percent yield) Theoretical Yield…...64.0g

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