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Unit 5: Stoichiometry

Unit 5: Stoichiometry. Section 1: Mole:Mole and Gram:Gram. Stoichiometry. Technical word for the relationships among balanced equations, moles, and grams Chemists use stoichiometry like cooks use cooking recipes. Mole-to-Mole Problems.

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Unit 5: Stoichiometry

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  1. Unit 5: Stoichiometry Section 1: Mole:Mole and Gram:Gram

  2. Stoichiometry • Technical word for the relationships among balanced equations, moles, and grams • Chemists use stoichiometry like cooks use cooking recipes

  3. Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? H2 + N2 NH3 Step 1: Balance the equation 3H2 + N2 2NH3

  4. Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 2NH3 Step 2: Identify the “given” and “unknown” provided in the problem, including the units G: 150 mol NH3 U: # mol H2

  5. Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 2NH3 G: 150 mol NH3 U: # mol H2 Step 3: Begin with the “given” # then choose a conversion factor that has in its denominator the same units as those in the “given” 150 mol NH3 x _______ mol NH3

  6. Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 2NH3 G: 150 mol NH3 U: # mol H2 Step 4: The numerator needs to have the same unit as your “unknown” 150 mol NH3 x mol H2 mol NH3

  7. Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 2NH3 G: 150 mol NH3 U: # mol H2 Step 5: Use the coefficients in the balanced equation that pertain to its unit to solve 150 mol NH3 x 3 mol H2 = 225 mol H2 2 mol NH3

  8. Mole-to-Mole Problems Ex-1: If you want to manufacture 150 moles of ammonia (NH3), how many moles of hydrogen will you need? 3H2 + N2 2NH3 G: 150 mol NH3 U: # mol H2 Step 6: Make sure your final answer is in the correct # of sig figs with its unit 150 mol NH3 x 3 mol H2 = 225 mol H2230 mol H2 2 mol NH3

  9. Mole-to-Mole Formula • “G” stands for “given” • “U” stands for “unknown” Use the coefficient from the balanced equation Use the coefficient from the balanced equation

  10. Mole-to-Mole Practice Ex-2: If you want to make 100 moles of ammonia (NH3), how many moles of nitrogen (N2) will you need? H2 + N2 NH3 50 mol N2

  11. Mole-to-Mole Practice Ex-3: If you have 36 moles of nitrogen (N2), how many moles of hydrogen (H2) will you need? H2 + N2 NH3 110 mol H2 or 1.1x102 mol H2

  12. Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? HF + SiO2 SiF4 + H2O Step 1: Balance the equation 4HF + SiO2 SiF4 + 2H2O

  13. Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 SiF4 + 2H2O Step 2: Identify the “given” and “unknown” provided in the problem, including the units G: 100 g HF U: # g SiO2

  14. Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 SiF4 + 2H2O Step 3: Begin with the “given” # then choose a conversion factor that has in its denominator the same units as those in the “given”… this is its molar mass. The numerator will always be 1 mole of the “given” units 100 g HF x 1 mol HF 20.0059 g HF

  15. Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 SiF4 + 2H2O Step 4: The 3rd conversion factor has moles of the “given” in its denominator and the moles of the “unknown” in its numerator. Take the numbers from the coefficients from the balanced equation. 100 g HF x 1 mol HF x 1 mol SiO2 20.0059 g HF 4 mol HF

  16. Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 SiF4 + 2H2O Step 5: The 4th conversion factor allows for the transition from moles SiO2 to grams SiO2 through molar mass 100 g HF x 1 mol HF x 1 mol SiO2 x 60.083 g SiO2 = 75.082 20.0059 g HF 4 mol HF 1 mol SiO2

  17. Gram-to-Gram Problems Ex-1: How many grams of glass (SiO2) can be etched by 100 grams of hydrofluoric acid (HF)? 4HF + SiO2 SiF4 + 2H2O Step 6: Make sure your final answer is in the correct # of sig figs with its unit 100 g HF x 1 mol HF x 1 mol SiO2 x 60.083 g SiO2 = 75.082 20.0059 g HF 4 mol HF 1 mol SiO2 80 g SiO2

  18. Gram-to-Gram Formula • “G” stands for “given” • “U” stands for “unknown” Use the coefficient from the balanced equation Use the coefficient from the balanced equation

  19. Gram-to-Gram Practice Ex-2: How many grams of glass (SiO2) can be made from 230 grams of H2O? 4HF + SiO2 SiF4 + 2H2O 380 g SiO2

  20. Gram-to-Gram Practice Ex-3: How many grams of silicon fluoride (SiF4) are needed to make 100.50 g of water? 4HF + SiO2 SiF4 + 2H2O 290.31 g H2O

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