Section 9.3 Limiting Reactants and Percent Yield Double Cheeseburgers and Stoichiometry 1 Bacon Double Cheeseburger needs 1 bun, 2 patties, 2 slices of cheese, 4 strips of bacon For 5 Double Cheeseburgers how many units of each ingredient do I need? Fill in the final column below with how many complete burgers I can make: BunsPattiesCheese Slices Bacon StripsHow Many Burgers?

Section 9.3 Limiting Reactants and Percent Yield 2 Reacting Amounts In a table setting, there is 1 plate, 1 fork, 1 knife, and 1 spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item?

Section 9.3 Limiting Reactants and Percent Yield 1.To understand the concept of limiting reactants 2.To learn to recognize the limiting reactant in a reaction 3.To learn to use the limiting reactant to do stoichiometric calculations 4.To learn to calculate percent yield Objectives

Section 9.3 Limiting Reactants and Percent Yield A. The Concept of Limiting Reactants Stoichiometric mixture –N 2 (g) + 3H 2 (g) → 2NH 3 (g)

Section 9.3 Limiting Reactants and Percent Yield Limiting reactant mixture A. The Concept of Limiting Reactants –N 2 (g) + 3H 2 (g) → 2NH 3 (g)

Section 9.3 Limiting Reactants and Percent Yield Limiting Reagent: the reagent that is completely used up in a chemical reaction. Excess Reagent: reagent not completely used up in a chemical reaction.

Section 9.3 Limiting Reactants and Percent Yield For a Limiting reactant mixture the number of moles are not balanced to match the reaction equation –N 2 (g) + 3H 2 (g) → 2NH 3 (g) A. The Concept of Limiting Reactants –Limiting reactant is the reactant that runs out first –When the limiting reactant is exhausted, then the reaction stops

Section 9.3 Limiting Reactants and Percent Yield B. Calculations Involving a Limiting Reactant

Section 9.3 Limiting Reactants and Percent Yield 9

Section 9.3 Limiting Reactants and Percent Yield Example How many moles of NH 3 can be formed from 3.0 mol of N 2 and 6.0 mol of H 2 ?

Section 9.3 Limiting Reactants and Percent Yield 11 Limiting Reactants Using Mass Calculate the mass of water produced when 8.00 g H 2 and 24.0 g O 2 react? 2H 2 (g) + O 2 (g) 2H 2 O(l)

Section 9.3 Limiting Reactants and Percent Yield 12 Limiting Reactants Using Mass Calculate the grams of H 2 for each reactant. H2:H2: 8.00 g H 2 x 1 mol H 2 x 2 mol H 2 O x g H 2 O g H 2 2 mol H 2 1 mol H 2 O = 71.5 g H 2 O O2:O2: 24.0 g O 2 x 1 mol O 2 x 2 mol H 2 O x g H 2 O g O 2 1 mol O 2 1 mol H 2 O = 27.0 g H 2 O. O 2 is the limiting reactant

Section 9.3 Limiting Reactants and Percent Yield Example: Work with your partner! A mixture of 1.50 mol of Al and 3.00 mol of Cl 2 are allowed to react. What is the limiting reactant? How many moles of AlCl 3 are formed? How many moles of excess reactant remain at the end of the reaction?

Section 9.3 Limiting Reactants and Percent Yield Example: Work on your own If you start with 25.0 grams of Lead (II) Nitrate and 15.0 grams of sodium iodide, how many grams of sodium nitrate can be formed? What is the difference between this example and the examples before?

Section 9.3 Limiting Reactants and Percent Yield Example: If you start with 25.0 grams of Lead (II) Nitrate and 15.0 grams of sodium iodide, how many grams of sodium nitrate can be formed? Assume the following:

Section 9.3 Limiting Reactants and Percent Yield C. Percent Yield Theoretical Yield –The maximum amount of a given product that can be formed when the limiting reactant is completely consumed. The actual yield (amount produced) of a reaction is usually less than the maximum expected (theoretical yield). Percent Yield –The actual amount of a given product as the percentage of the theoretical yield.

Section 9.3 Limiting Reactants and Percent Yield We NEVER make as much product as stoichiometry says Human error: “you messed it up” –Biggest cause of error Instrument error: “the machine messed it up” –Minor cause of error Unknown error: “I don’t know….but something messed it up” –Usually found to be human error

Section 9.3 Limiting Reactants and Percent Yield According to his pre-lab theoretical yield calculations a student’s experiment should have produced 1.44g of magnesium oxide. When he weighed his product after reaction, only 1.23g of magnesium oxide was present. What is the student’s percent yield?