Stoichiometry based on the law of conservation of mass The study of quantitative relationships between the amount of reactants used and the amounts of products formed by a chemical reaction.

Relationships 4 Fe(s) + 3 O2 (g) → 2 Fe2O3 (s) 4 atoms Fe + 3 molecules O2 → 2 units Fe2O3 4 moles Fe + 3 moles O2 → 2 moles Fe2O3 319.40g 223.40 g 96.00 g

Chocolate Chip Cookies!! 1 cup butter 1/2 cup white sugar 1 cup packed brown sugar 1 teaspoon vanilla extract 2 eggs 2 1/2 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 2 cups semisweet chocolate chips Makes 3 dozen How many eggs are needed to make 3 dozen cookies? How much butter is needed for the amount of chocolate chips used? How much brown sugar would you need if you had 1 ½ cups white sugar?

Example Bridge Problem How much flour would you need if you needed 10.5 dozen cookies? 10.5 dz cookies 2.5 cups flour = 3 dz cookies 8.75 cups flour 2.5 cups flour = 3 dz cookies

Practice Write the balanced reaction for hydrogen gas reacting with oxygen gas. 2 H2 + O2  2 H2O How many moles of reactants are needed? What if we wanted 4 moles of water? What if we had 3 moles of oxygen, how much hydrogen would we need to react and how much water would we get? What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced?

Mole Ratios Coefficients indicate relationship between moles of reactants and products. MOLE RATIO = ratio between numbers of moles of ANY two substances in a balanced chemical equation.

Stoichiometry Steps Core step in all stoichiometry problems!! 1. Write a balanced equation. 2. Identify given & find. 3. Line up conversion factors. Mole ratio - moles  moles Molar mass - moles  grams Mole ratio - moles  moles Core step in all stoichiometry problems!! 4. Solve & Check answer. 5. Don’t forget Significant Figures!