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Stoichiometry

Stoichiometry. Chapter 11 (page 326). Essential Question!!. Why do scientist compare mole ratios, and why is it important in chemical reactions??. Vocabulary: Section 1. Stoichiometry Moles Stoichiometric equivalent Mole ratio Gram to gram calculations. Chemical equations tell stories….

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Stoichiometry

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  1. Stoichiometry Chapter 11 (page 326)

  2. Essential Question!! • Why do scientist compare mole ratios, and why is it important in chemical reactions??

  3. Vocabulary: Section 1 • Stoichiometry • Moles • Stoichiometric equivalent • Mole ratio • Gram to gram calculations

  4. Chemical equations tell stories… But what exactly do they tell us? 2CO(g) + O2(g) 2CO2(g) They tell us what compounds we start with: Carbon monoxide (CO) gas Oxygen (O2) gas what compounds are formed: Carbon dioxide (CO2) gas

  5. 2CO(g) + O2(g) 2CO2(g) Chemical equations tell stories… What else do they tell us? 2CO molecules 1O2 molecules 2CO2 molecules They tell us how much of each compound is involved stoichiometry: the study of the amounts of substances involved in a chemical reaction.

  6. 2CO(g) + O2(g) 2CO2(g) 2 CO molecules 2 dozen CO molecules 2 moles CO molecules 2 x (6.023 x 1023)CO molecules 2CO2 molecules 2 dozen CO2 molecules 2 moles CO2 molecules 2 x (6.023 x 1023) CO2 molecules 1O2 molecules 1 dozen O2 molecules 1 mole O2 molecules (1 x) 6.023 x 1023 O2 molecules

  7. 2CO(g) + O2(g) 2CO2(g) Is that okay? Number of moles is notconserved + ≠ 2 moles CO molecules 1 mole O2 molecules 2 moles CO2 molecules

  8. 2CO(g) + O2(g) 2CO2(g) 2 C atoms 2 O atoms 2 O atoms 2 C atoms 4 O atoms Number of atoms is conserved = + = This chemical equation isbalanced

  9. Coefficients are important 1 bag cake mix + 3 eggs + ¼ cup oil + 1 cup water 1 batch cupcakes Write as a ratio:

  10. Coefficients are important Fermentation of sugar (glucose) into alcohol: C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g) 1 mole glucose 2 moles ethanol 2 moles carbon dioxide 1 moles 3 moles 7.5 moles 2 moles 6 moles 15 moles x 3 ethanol/ carbon dioxide x 7.5 glucose will yield

  11. Fermentation of sugar (glucose) into alcohol: C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g) 1 mole glucose 2 moles ethanol 2 moles carbon dioxide Write as a ratio: mole ratio: a ratio comparison between substances in a balanced equation. It is obtained from the coefficients in the balanced equation.

  12. Mole ratios Consider the following equation: CO(g) + 2H2(g) CH3OH(l) carbon monoxide hydrogen methanol Compare the reactant CO to the product CH3OH.

  13. Stoichiometry 1. Mass of substance A 3. Amount in mol of substance B Convert by dividing by the molar mass of A B 2. Amount in mol of Substance A Convert using the mol ratio A Convert by mult. by molar mass of B 4. Mass of Substance B given in the chemical equation

  14. Process for calculating grams from grams given

  15. Method Mass - Mass mass A mass B = coeff A X FM A coeff B X FM B

  16. Method Mass - Volume mass A vol B = coeff A * FM A coeff B * 22.4

  17. Method Volume - Volume vol B Vol A * coeff B coeff A

  18. Assignment Take a new sheet of paper and fold it into three sections Write your name, the title of the chapter and the number On the first section from the sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

  19. 1.Given the equation N2 + 3 H2 2NH3 If 4.00 mol of H2 react, how many mol of NH3 will be produced? 2 2.66 mol = 4.0 mol X 3

  20. How many moles of sodium will react with water to produce 4.00 mol of Hydrogen?2 Na + 2H2O  2 NaOH + H2 2 8 mol sodium = 4 mol H2 X 1

  21. How many moles of H2SO4 will react with 18.0 mol of Al?2 Al + 3 H2SO4 Al2(SO4)3 + 3 H2 3 18.0 mol Al X = 27.0 moles 2

  22. What mass of KClO3 do you need to produce 0.50 mol of O2?2 KClO3 2 KCl + 3 O2 2 0.50 mol X 0.33 mol KClO3 = 3 0.33 mol KClO3 X 122.6 g/mol = 40.866 g

  23. What mass of Zn metal do you need to produce 0.50 mol of ZnCl2?Zn (s) + 2HCl  ZnCl2(s) + H2(g) 1 0.50 mol X 0.5 Zn = 1 0.5 mol Zn X 65.4 g/mol = 32.7 g Zn

  24. What mass of NH3 do you need to produce 0.25 mol of H2?N2 + 3H2(g)  2 NH3 3 0.25 mol X 0.375 H2 = 2 0.375 mol H2 X 0.75 g/mol = 0.75 g H2

  25. Assignment • Write a three dollar summary of this section (based on what you learned) and using three vocabulary words learned • Answer questions # 1- 3 on page 360 • Turn in completed work • Honors Chemistry Homework: • Page 362 # 38 - 45

  26. Vocabulary: Section 2 • Percent yield • Actual yield • Theoretical yield

  27. In theory, all 100 kernels should have popped. Did you do something wrong? + 100 kernels 82 popped 18 unpopped

  28. Percent yield What you get to eat! + 100 kernels 82 popped 18 unpopped

  29. actual yield: the amount obtained in the lab in an actual experiment. theoretical yield: the expected amount produced if everything reacted completely.

  30. Percent yield in the lab Decomposition of baking soda: 2NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g) 10.00 g 4.87 g measured experimentally Can you think of reasons why the final mass of Na2CO3 may not be accurate? (What could be sources of error?) - There is usually some human error, like not measuring exact amounts carefully - Maybe the heating time was not long enough; not all the Na2HCO3 reacted - Maybe Na2CO3 was not completely dry; some H2O(l) was measured too - CO2 is a gas and does not get measured

  31. Percent yield in the lab Decomposition of baking soda: 2NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g) 10.00 g 4.87 g measured experimentally Let’s calculate the percent yield obtained in experiment calculated

  32. Conversions of Mass to Amounts In Moles Example

  33. Mass to Mass Calculations Example

  34. Assignment • Write a three dollar summary of this section (based on what you learned) • Answer questions # 4- 6 on page 360 • Turn in completed work • Honors Chemistry Homework • Page 363 # 46 - 57

  35. Vocabulary: 3 • Limiting reactant • Excess reactant

  36. Suppose you want to make 2 ham & cheese sandwiches Recipe: 2 ham & cheese sandwich 4 slices of bread 4 slices of ham 2 slices of cheese

  37. Suppose you want to make 2 ham & cheese sandwiches Can you still make 2 ham & cheese sandwiches if you have 4 slices of bread, 4 slices of ham, and 1 slice of cheese? Limiting factor No, you are limited by the cheese! You can only get 1 ham & cheese sandwich.

  38. Limiting Reactants • A limiting reactant is the reactant that limits the amount of the other reactants that can combine to form product in a chemical reaction • An excess reactant is the reactant that is left over after the other reactant runs out, or the reaction is completed

  39. Excess reactant For a chemical reaction: Reactant A is in excess so the reaction will stop when you run out of reactant B. Reactant B is the limiting reactant. The amount of product C will depend on how much reactant B is present.

  40. Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) 1. What is the limiting reactant? 150 g 60 g Step 1: Convert masses to moles Step 2: Use mole ratios to find the limiting reactant

  41. Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) 1. What is the limiting reactant? 150 g 60 g Step 1: Convert masses to moles available Fe2O3 available Al Step 2: Use mole ratios to find the limiting reactant needed to react with all Fe2O3 needed to react with all Al

  42. Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) 1. What is the limiting reactant? 150 g 60 g Step 1: Convert masses to moles available Fe2O3 availableAl Step 2: Use mole ratios to find the limiting reactant needed to react with all Fe2O3 needed to react with all Al

  43. Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) 1. What is the limiting reactant? 150 g 60 g available Fe2O3 There is not enough Fe2O3 available to react with all the Al, so Fe2O3 is the limiting reactant needed to react with all Al

  44. Example # 1 & 2

  45. The Haber-Bosch process for the synthesis of ammonia: N2(g) + 3H2(g) → 2NH3(s)

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