I. I.Stoichiometric Calculations The Big Kahuna Stoichiometry

StoichiometryStoichiometry Greekstiocheion – element metron – measure

Proportional Relationships b Stoichiometry is all about proportional relationships. Certain amounts of ingredients are needed to make certain amounts of food or other things. b In our case, the ingredients are the reactants and the food is the products.

A. Proportional Relationships b I have 5 eggs. How many cookies can I make? 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. 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 Ratio of eggs to cookies X

1 stick + 2 gloves = 1 player 2 sticks: 8 gloves: 5 gloves: needs 4 gloves to make 2 players needs 4 sticks to make 4 players makes 2.5 players

b Stoichiometry mass relationships between substances in a chemical reaction based on the mole ratio b Mole Ratio indicated by coefficients in a balanced equation 2 Mg + O 2  2 MgO

b We can read this in several ways: 1. For every 1 mole of oxygen used, 2 moles of magnesium oxide are formed. 2. For every 2 moles of magnesium used, 1 mole of oxygen is required. b Come up with two similar sentences to these ones that are also true. 2 Mg + O 2  2 MgO

B. Stoichiometry Steps 1. Write a balanced equation. 2. Identify known & unknown. 3. Determine conversion factors. Mole ratio - moles  moles Molar mass -moles  grams Core step in all stoichiometry problems!! 4. Calculate unknown

C. Stoichiometry Problems Ex 1) How many moles of KClO 3 must decompose in order to produce 9 moles of oxygen gas? 9 mol O 2 2 mol KClO 3 3 mol O 2 = 6 mol KClO 3 2KClO 3  2KCl + 3O 2 ? mol9 mol

Ex 2) How many grams of silver will be formed from 12.0 g copper? Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 sm = 12.0 g mass = ? # moles Cu = mm sm # moles Cu = g/mol 12.0 g # moles Cu = mol # moles Ag = mol mass Ag = (0.378 mol) ( g/mol) mass Ag = g mass Ag = (# mol) (mm)

Ex 3) If you dropped 75.0 g of aluminum into sulfuric acid, how many grams of hydrogen gas would be produced? 2Al + 3 H 2 SO 4  Al 2 (SO 4 ) 3 + 3H 2 sm = 75.0 gmass = ? # moles Al = mm sm # moles Al = g/mol 75.0 g # moles Al = 2.78 mol # moles H 2 = 4.17 mol mass H 2 = (# mol) (mm) mass H 2 = (4.17 mol)(2.016 g/mol) mass H 2 = 8.41 g

AssignmentAssignment 1. Stoichiometry: Mass-Mass problems from the workbook.