Using Chemical Equations Aim CE6 – How does a chemical equation allow you to determine how much you can make?

Stoichiometry A branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions In stoichiometry, chemical equations are used to determine o The number of reactants required in a chemical reaction o The number of products produced from the chemical reaction o How much product is made when more or less reactant is used

Chemistry in the Kitchen In the kitchen, just as in chemistry, ingredients (reactants) are mixed together to create pancakes or cookies (products) In stoichiometry, reactants take the place of ingredients  1 cup + 2 cups + 1 cup yields 4 cups

Remember the Law of Conservation of Matter! The amount of mass you start with equals the amount of mass you end up with In order to make double the amount of pancakes, we need double the amount of all our ingredients  1 cup + 2 cups + 1 cup yields 4 cups

Example of using stoichiometry and chemical equations Balance: 2 H O 2  2 H 2 O Q: How many hydrogen molecules combine with molecules of oxygen to form water? Q: What is the ratio of H 2 to O 2 ? 2:1 Q: What is the ratio of H 2 to H 2 0? 2:2 Q: What is the ratio of O 2 to H 2 O 1:2 Q: What if you double the number of H 2 molecules without doubling the O 2 ? Nothing! You will run out of O 2 first!

Balanced: 2 H 2 + O 2  2 H 2 O Q: If you have 4 molecules of H 2, and unlimited O 2 molecules, how many water molecules will you make? 4 molecules – the ratio of H 2 to H 2 0 is equal in the equation – 2:2 is the same as 4:4 Q: If you have 2 molecules of H 2, and 2 molecules of O 2, how many molecules of water would you make? 2 molecules – the ratio of molecules of hydrogen to water is the same Q: If you have 100 molecules of H 2, how many molecules of O 2 do you need to use up all H 2 ? 50 molecules - use a proportion!

Using the Cassans Method of Stoichiometry A chemist wants to determine how many moles of oxygen he will yield from 32.8 moles of peroxide according to the balance equation: 32.8 X 2 H 2 O 2  2 H 2 O + 1 O 2 Step 1 – place the new moles from the problem over the corresponding known moles in the rxn Step 2 – place X over the substance whose amount you want to determine Step 3 – solve as a proportion 32.8 moles H 2 O 2 = X moles O 2 2 moles H 2 O 2 1 mole O 2 X = 16.4 moles of O 2

1. Using the following equation: 2 Na + Cl 2  2 NaCl How much salt will be made if 2.5 moles of chlorine are used? 2.Using the following equation: 2 Al + 3 CuCl 2  2 AlCl Cu How much copper will be made when 0.25 moles of aluminum react with unlimited copper II chloride? 3.Using the following equation: 2 Na + 2 H 2 O  H NaOH How much water will be needed to completely react with 8.0 moles of Na?