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Using Stoichiometry

Using Stoichiometry. Chemists use stoichiometry to predict amounts of reactants used and products formed in specific reactions. Always start with a balanced equation. This tells you the correct amount of moles for each substance. N₂ + 3H₂ → 2NH₃. Like a recipe. Peanut Butter Cookies

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Using Stoichiometry

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  1. Using Stoichiometry Chemists use stoichiometry to predict amounts of reactants used and products formed in specific reactions

  2. Always start with a balanced equation • This tells you the correct amount of moles for each substance N₂ + 3H₂ → 2NH₃ Like a recipe

  3. Peanut Butter Cookies 1 cup butter 1 tsp. vanilla 1 cup sugar 3 cups flour 1 cup brown sugar 2 tsp. baking soda 2 eggs ¼ tsp. salt 1 cup peanut butter makes 24 cookies What if I need 48 cookies? What if I want only 12 cookies? What if I need 5 dozen? If 3 cups of peanut butter are used, how many cookies will I get?

  4. 2K + 2H₂O → 2KOH + H₂ • Potassium reacts with water to produce potassium hydroxide and hydrogen • 2 mol potassium makes 1 mol hydrogen How much hydrogen is produced if only 0.0400 mol of potassium is used?

  5. Review mole ratios 2K + 2H₂O → 2KOH + H₂ Which two ratios deal with potassium and hydrogen?

  6. Mole to Mole Conversion 1. balance equation 2. Use correct mole ratio Moles of known x Moles of unknown = Moles of Moles of known unknown

  7. 2K + 2H₂O → 2KOH + H₂ Moles of known x Moles of unknown = Moles of Moles of known unknown 0.0400 mol K x 1 mol H₂ = 0.0200 mol H₂ 2 mol K

  8. Try it! • One disadvantage of burning propane (C₃H₈) is that carbon dioxide (CO₂) is one of the products. How many moles of CO₂ is produced when 10.0 mol of C₃H₈ is burned in excess oxygen in a gas grill? What is first step?

  9. C₃H₈ + 5O₂ → 3CO₂ + 4H₂O • Use correct mole ratio Moles of known x Moles of unknown = Moles of Moles of known unknown

  10. Mole to Mass Conversion • If you know the moles of a reactant and you want to know the mass of a product

  11. Mole to Mass Conversion • Balance equation • Use correct mole ratio • Multiply by molar mass

  12. What is the mass of NaCl when Na reacts with 1.25 mol Cl gas? 1. Balance the equation

  13. 2Na + Cl₂ = 2NaCl 2. Use correct mole ratio 1.25 mol Cl₂ x 2 mol NaCl = 2.50 mol NaCl 1 mol Cl₂

  14. 2Na + Cl₂ = 2NaCl 2.50 mol NaCl 3. Multiply by molar mass

  15. When working in a lab, you will be working with grams to measure out substances… Mass to Mass Conversions

  16. Mass to Mass Conversions • Balance equation • Convert grams to moles of known substance • Use correct mole ratio • Multiply by molar mass

  17. MacGyver saves the day again! • MacGyver offers to help some criminals break into an armored vehicle in order to save a life Chemistry in Action!!!

  18. http://www.youtube.com/watch?v=fF6FUVxAVzI

  19. Mass to Mass Conversion • 3Mg + Fe₂O₃ → 3MgO + 2Fe + lots of heat How many grams of Mg does MacGyver need to make 5.0 g of Fe?

  20. 3Mg + Fe₂O₃ → 3MgO + 2Fe + heat • Balance equation • Convert grams to moles of known substance 5.0 g Fe = ? Mol / molar mass Fe

  21. 5.0 g Fe = .0895 mol Fe 3. Use correct mole ratio 3Mg + Fe₂O₃ → 3MgO + 2Fe + heat Moles of known x Moles of unknown = Moles of Moles of known unknown

  22. 0.134 mol Mg 4. Multiply by molar mass 0.134 x 24.305 = 3.26 g Mg

  23. Review

  24. Worksheet!

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