I. I.Stoichiometric Calculations (Ch. 12 p ) Stoichiometry – Ch. 12

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

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

B. Stoichiometry Steps 1. Write a balanced equation. 2. Write the given/known. 3. Use conversion factors (mole equalities) to cancel units… A. Convert to moles B. use mole ratio (coefficients) to change into new substance, C. then convert to new desired units. 4. Check answer.

Mole ratio - moles  moles Molar mass -moles  grams Molarity - moles  liters soln Molar volume -moles  liters gas b Core step in all stoichiometry problems!!

1 mol of a gas=22.4 L at STP C. Molar Volume at STP S tandard T emperature & P ressure 0°C and 1 atm

C. Other mole equivalents b 1 mole = 22.4 Liters of gas (must be in gas form at STP) b 1 mole = 6.02 x particles (atoms, mc’s, formula units, ions) b 1 mole = Molar Mass in grams (using the periodic table masses)

C. Molar Volume at STP Molar Mass (g/mol) 6.02  particles/mol MASS IN GRAMS MOLES NUMBER OF PARTICLES LITERS OF SOLUTION Molar Volume (22.4 L/mol) LITERS OF GAS AT STP Molarity (mol/L)

D. Stoichiometry Problems b 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

D. Stoichiometric Calculations b Special Case: If converting Liters to Liters, the mole ratio can be used ONLY IF all substances are gas. All other units MUST be changed to moles first. 9 L H 2 O 1 L O 2 2 L H 2 O = 4.5 L O 2 2H 2 (g) + O 2 (g)  2H 2 O(g) ? L O 2 needed? 9 Liter produced

b How many grams of KClO 3 are req’d to produce 9.00 L of O 2 at STP? Convert to moles first!!! 9.00 L O 2 1 mol O L O 2 = 32.8 g KClO 3 2 mol KClO 3 3 mol O g KClO 3 1 mol KClO 3 ? g 9.00 L D. Typical Stoichiometry 2KClO 3  2KCl + 3O 2

D. Stoichiometry Problems b How many grams of silver will be formed from 12.0 g copper? 12.0 g Cu 1 mol Cu g Cu = 40.7 g Ag Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 2 mol Ag 1 mol Cu g Ag 1 mol Ag 12.0 g? g

63.55 g Cu 1 mol Cu D. Stoichiometry Problems b How many grams of Cu are required to react with 1.5 L of 0.10M AgNO 3 ? 1.5 L.10 mol AgNO 3 1 L = 4.8 g Cu Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 1 mol Cu 2 mol AgNO 3 ? g 1.5L 0.10M

E. Key things to remember b To be safe, consider there to be two variables, the chemical formula and the units. b Only change one variable within each conversion.