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Understanding Basic Stoichiometry Through Chemical Reactions and Recipes

This guide introduces stoichiometry, the quantitative study of chemical reactions, by likening it to baking. The basic question of stoichiometry is "how much?" illustrated with a cupcake recipe. It explains how to derive molar ratios from balanced equations, like the decomposition of aluminum oxide. The document explores how to calculate moles of reactants and products, using practical examples to enhance comprehension. By mastering stoichiometry, students gain essential skills in quantifying chemical reactions.

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Understanding Basic Stoichiometry Through Chemical Reactions and Recipes

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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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