Stoichiometry: Chemical Reactions are like Recipes How much reactant is needed to make a certain amount of product?

Dozen = 12 Case = 24 Ream = 500

Units A dozen eggs = 12 eggs A case of coke = 24 cans A ream of paper = 500 sheets A century = 100 years In Chemistry, we use… Mole: It is a unit equal to x atoms or molecules This number is called Avogadro’s Number, in honor of Amadeo Avogadro.

How Big is a Mole? -One mole of marbles would cover the entire Earth (oceans included) for a depth of three miles. -One mole of $100 bills stacked one on top of another would reach from the Sun to Pluto and back 7.5 million times.

Molar Mass Molar Mass: The mass of 1 mole of substance. 1 mole of carbon contains x atoms and has a mass of grams. Unit: g/mol Carbon’s molar mass is g/mol

Molar Mass ZnCl 2 : 1 Zn: 1 x g/mol = g/mol 2 Cl: 2 x g/mol = g/mol Molar Mass: g/mol

Molar Mass ZnSO 4 : 1 Zn: 1 x g/mol = g/mol 1 S: 1 x g/mol = g/mol 4 O: 4 x g/mol = g/mol Molar Mass = g/mol

General Plan for Converting Mass, Amount, and Number of Particles Mass of substance (grams) Amount of Substance in Moles Number of Atoms or molecules Use the molar mass Use Avogadro’s Number

Sample Problem 1. A chemist has a jar containing g of iron. How many moles of iron does the jar contain?

Sample Problem 2. A student needs mol of zinc for a reaction. What mass of zinc in grams should the student use?

Sample Problem 3. How many moles of lithium are there in x lithium atoms?

Chemical Equations are like Cooking Recipes

Recipe makes 5 dozen cookies. Velasquez has 5 eggs. How many dozens of cookies can she make? 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 5 eggs5 doz. 2 eggs = 12.5 dozen cookies “Mole Ratio” of eggs to cookies Courtesy Christy Johannesson

Recipe makes 5 dozen cookies. Henkels has 9 cups of chocolate chips. How many dozens of cookies can he make? 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 5 eggs5 doz. 2 eggs = 12.5 dozen cookies “Mole Ratio” of eggs to cookies Courtesy Christy Johannesson

Proportional Relationships: S’more Activity 2 Gc + 1 M + 4 Cp  1 Sm If each student is to make one S’more, and I have 30 students, how many graham crackers & chocolate pieces will I need? Given: 30 S’mores Unknown: ? Gc, ? Cp 30 S’mores 2 Gc 1 S’more = ? “Mole Ratio” 30 S’mores 4 Cp 1 S’more = ? “Mole Ratio”

Stoichiometry Diagram Mass Particles Volume Mole Mass Volume Particles Given Unknown Substance A Substance B Use periodic table 1 mole = molar mass (g) Mole Ratio Use coefficients from balanced chemical equation 1 mole = 22.4 L STP 1 mole = x particles (atoms or molecules) 1 mole = 22.4 L STP 1 mole = x particles (atoms or molecules) Use periodic table 1 mole = molar mass (g) (gases)

Mole Ratio 2Al 2 O 3(l)  4Al (s) + 3O 2(g) 2 molecules4 atoms3 molecules 2 dozen4 dozen3 dozen 2 moles4 moles3 moles -The coefficients of this equation tells us that for every 2 moles of aluminum oxide, it produces 4 moles of solid aluminum and 3 moles of oxygen molecules. -The mole ratio, a conversion factor between two amounts in a chemical reaction. It is indicated by the coefficients of the chemical equation. Mole Ratios: 2 mol Al 2 O 3 4 mol Al 4 mol Al2 mol Al 2 O 3 2 mol Al 2 O 3 3 mol O 2 3 mol O 2 2 mol Al 2 O 3

Stoichiometry Examples: Using Mole Ratios How many moles of KClO 3 must decompose in order to produce 9 moles of oxygen gas? Given: 9 mol O 2 gas Unknown: ? mol KClO 3 9 mol O 2 2 mol KClO 3 3 mol O 2 = 6 mol KClO 3 2 KClO 3  2 KCl + 3 O 2 ? mol9 mol Courtesy Christy Johannesson

Stoichiometry Examples: Using Mole Ratios How many moles of KCl are produced when 10 moles of oxygen gas are formed? Given: 10 mol O 2 gas Unknown: ? mol KCl 10 mol O 2 2 mol KCl 3 mol O 2 = 6.67 mol KCl Courtesy Christy Johannesson 2 KClO 3  2 KCl + 3 O 2 ? mol10 mol