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Stoichiometry

Stoichiometry. Quantitative study of chemical reactions The basic question - how much? - is the object of stoichiometry. It’s like baking a cake…or two. Basic cupcake recipe:. 2 ¼ cups all purpose flour 1 1/3 cups sugar 3 teaspoons baking powder ½ teaspoon salt ½ cup shortening

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Stoichiometry

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  1. Stoichiometry Quantitative study of chemical reactions The basic question - how much? - is the object of stoichiometry. It’s like baking a cake…or two.

  2. Basic cupcake recipe: • 2 ¼ cups all purpose flour • 1 1/3 cups sugar • 3 teaspoons baking powder • ½ teaspoon salt • ½ cup shortening • 1 cup milk • 1 teaspoon vanilla • 2 large eggs • Makes 12 cupcakes • What if you wanted 24? • What if 8? • What if you only have 2 cups of flour/ • No measuring cup? • (48tsp = 1 cup)

  3. 2 4 3 Basic Stoichiometry • From the balanced equation we can determine the molar ratios. • Remember that the coefficients refer to the number of moles of each reactant or product there are in the balanced equation. • So in this equation 2 moles of aluminum oxide decompose to form 4 moles of aluminum metal and 3 moles of oxygen gas. • Always starts with a balanced equation (the recipe). Al2O3 Al + O2

  4. Basic Stoichiometry • What if I only had one mole of aluminum oxide. How many moles of aluminum metal could I produce then? • How many moles of oxygen gas? • What if I had three moles of aluminum oxide…? • Note, you always need the molar ratio to determine the number of moles produced from or required…. 2Al2O3  4Al+3O2

  5. 3 moles Al2O3 3moles O2 3 x 3 2 = 2 moles Al2O3 Molar ratio This is your “given” Basic Stoichiometry = 4.5mols of O2

  6. Try some • If you had 1 mole of aluminum oxide, how many moles of oxygen would you yield? • 1.5 moles • How many moles of aluminum oxide would you need to produce 17.25 moles of aluminum? • 8.625 moles. 2Al2O3  4Al+3O2

  7. Basic Stoichiometry • Remember that one mole can be converted to a substance’s mass in grams. • What is the mass in grams of one mole of aluminum? • So, what would be the mass of four moles of aluminum? • What if you had three moles of aluminum oxide? 2Al2O3  4Al+3O2

  8. 3 moles Al2O3 4 moles Al 3 x 4 x 27.0 2 27.0 g Al = 2 moles Al2O3 1 mole Al Molar ratio This is your “given” Converts moles of Al to grams of Al Basic Stoichiometry 2Al2O3  4Al+3O2 • Now the bridge looks like this:

  9. Practice • Page 359 #9-12

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