Stoichiometry The mathematics of chemical equations.

Toll House Cookie Recipe 2 cups flour + 1 tsp baking soda + 1 cup butter + 1 cup sugar + 1 cup brown sugar + 1 tsp vanilla + 2 eggs + 2 cups chocolate chips  24 cookies

1. How many cups of butter do you need to make 48 cookies? 48 cookies x 1 cup butter 24 cookies 2. How many eggs would you need to make 34 cookies? 34 cookies x ________ 3. If you have 7.5 cups of brown sugar how many cookies can you make? 4. If you have 5 cups of chocolate chips how many cookies can you make?

Stoichiometry Coefficients tell relative number of molecules, moles, or relative volume. Crossing the Bridge: moles of known x coefficient of unknown coefficient of known

Volume – Volume Problems Avogardro’s hypothesis: equal volumes of all gases at the same temperature and pressures contain the same number of molecules. All volumes must be at STP.

Volume to Volume Problems Example: 2 H2 + 02  2 H20 If you have 5 liters of oxygen how much water can you produce? moles known x coefficent of unknown coefficent of known

Mass-Mass Problems Mass is related to moles. Start with a balanced equation. 1. Change mass given to moles. (use molar mass) 2. Change to unknown moles (use mole ratio from equation) 3. Change moles to mass (use molar mass.)

Example: Mass to Mass Problem 2H2 + O2 ------------------> 2 H2O If there is 64.0 grams of oxygen, how many grams of water can be produced?

Example 2: Mass to Mass Problem Mg + 2 HCl --------------> MgCl2 + H2 How many grams of magnesium metal are needed to produce 34 grams of hydrogen?

Example 3 Mass to Mass Mg + 2 HCl --------------> MgCl2 + H2 How many grams of HCl are needed to react completley with 22 g of magnesium?

Mass-Volume Problems Start with a balanced equation. Change given quantity to moles. a. for mass, find molar mass. b. for volume, use 22.4 L at STP “Cross the Bridge.” Convert moles of unknown into desired quantity. b. for volume, use 22.4 L.

Limiting Reactants Limiting Reactant- the reactant that produces the least amount of product. The reactant that runs out first. 1.Using each reactant, determine the amount of product. 2.Which ever gives the least amount is the limiting reactant.

2 H2 + O2  2 H20 In an experiment, 20.0g of hydrogen and 36.0g of oxygen were mixed. Identify the limiting reactant.

Percent Yield “efficiency of the reaction” Actual yield/theoretical yield x 100 Actual yield is given in the problem. Theoretical yield is determined by stoichiometry.