Stoichiometric Calculations (p. 352 – 367) Stoichiometry – Ch. 12 Stoichiometric Calculations (p. 352 – 367)

A. Proportional Relationships 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. I have 5 eggs. What is the maximum number of cookies I can make? 5 dozen cookies 2 eggs Ratio of eggs to cookies 5 eggs = 12.5 dozen cookies

A. Proportional Relationships Stoichiometry mass relationships between substances in a chemical reaction based on the mole ratio Mole Ratio indicated by coefficients in a balanced equation 2 Mg + O2  2 MgO

B. Interpreting Chemical Equations Hydrogen gas reacts with oxygen gas. H2(g) + O2(g)  H2O(g) What does this tell us? 2 moles H2 + 1 mole O2  2 moles H2O Convert moles to grams!! 4.04 g H2 + 32.00 g O2  36.04 g H2O 36.04 g reactants  36.04 g products Mole Ratios: 2 H2 : 1 O2 : 2 H2O 2 2

B. Interpreting Chemical Equations Write the equation for the combustion of propane (C3H8). C3H8(g) + O2(g)  CO2(g) + H2O(g) What does this tell us? 1 mole C3H8 + 5 moles O2  3 moles CO2 + 4 moles H2O Mole Ratios: 1 C3H8 : 5 O2 : 3 CO2 : 4 H2O 5 3 4

C. Stoichiometry Steps 1. Write a balanced equation. 2. Identify and label known & unknown. 3. Line up conversion factors. Mole ratio – moles  moles Molar mass – moles  grams Molarity – moles  liters soln Molar volume – moles  liters gas Mole ratio – moles  moles Core step in all stoichiometry problems!! 4. Check answer.

D. Stoichiometry Problems How many moles of KClO3 must decompose in order to produce potassium chloride and 9 moles of oxygen gas? 2KClO3  2KCl + 3O2 ? mol 9 mol 9 mol O2 2 mol KClO3 3 mol O2 = 6 mol KClO3

D. Stoichiometry Problems – Mole-Mole NO + O2  NO2 BE SURE TO BALANCE THE EQUATION FIRST!! If you start with 3.6 moles O2, how many moles NO2 will be produced? 2 2 3.6 mol ? mol 3.6 mol O2 2 mol NO2 1 mol O2 = 7.2 mol NO2

D. Stoichiometry Problems – Mole-Mole See handout – “Stoichiometry Practice Problems” Work on “Part A: Mole-Mole” Problems

E. Stoichiometry Problems – Mole-Mole LiBr(aq) + Cl2 (g)  LiCl(aq) + Br2(l) How many moles of lithium chloride will be formed from 0.046 mol of lithium bromide? 2 2 ? mol 0.046 mol 0.046 mol LiBr 2 mol LiCl 2 mol LiBr = 0.046 mol LiCl

Stoichiometry Diagram Moles – given Moles – unknown Mole Ratio Molar Mass Molar Mass Grams – given Grams – unknown

F. Stoichiometry Problems – Mole/Mass In photosynthesis, carbon dioxide and water react to form glucose, C6H12O6 and oxygen gas. ___CO2 + ___H2O  ___C6H12O6 + ___O2 A. If 15.6 grams of carbon dioxide react, how many moles of glucose will be produced? B. How many grams of carbon dioxide must react to produce 0.25 moles of glucose? B – ? g 0.25 mol A – 15.6 g ? mol 6 6 6 15.6 g CO2 1 mol CO2 1 mol C6 H12O6 = 0.0591 mol C6H12O6 44.01 g CO2 6 mol CO2 0.25 mol C6 H12O6 6 mol CO2 44.01 g CO2 = 66 g CO2 1 mol C6 H12O6 1 mol CO2

F. Stoichiometry Problems See handout – “Stoichiometry Practice Problems” Work on Handout – “Part B: Mole-Mass” Problems

G. Stoichiometry Problems – Mass/Mass How many grams of silver will be formed from 12.0 g copper (II) reacting with silver nitrate? Cu + 2AgNO3  2Ag + Cu(NO3)2 12.0 g ? g 12.0 g Cu 1 mol Cu 63.55 g Cu 2 mol Ag 1 mol Cu 107.87 g Ag 1 mol Ag = 40.7 g Ag

G. Stoichiometry Problems – Mass/Mass Sodium metal reacts with oxygen gas to produce solid sodium oxide. How many grams of sodium must react to produce 42.0 grams of sodium oxide? 4Na + O2  2Na2O ? g 42.0 g 42.0 g Na2O 1 mol Na2O 4 mol Na 22.99 g Na = 31.2 g Na 61.98 g Na2O 1 mol Na 2 mol Na2O

G. Stoichiometry Problems Work on the rest of the handout: Part C: Mass to Mole Part D: Mass to Mass Classwork/Homework

Stoichiometry WS Problem 1 How many grams of hydrogen gas would be needed to form 8.0 grams of water? 2 H2 + O2  H2O 2 ? g 8.0 g 8.0 g H2O 2 mol H2 H2O 1 mol H2O 2.02 g H2 1 mol = 0.90 g H2 18.02 g H2O