Section 9.3 Limiting Reactants and Percent Yield 1.Define the terms theoretical yield and actual yield. 2.Calculate percent yield 3.Identify reasons that a percent yield may not by 100% Objectives

Section 9.3 Limiting Reactants and Percent Yield Percent Yield Theoretical Yield –The maximum amount of a given product that can be formed when the reactants are completely consumed. (as calculated in a stoichiometry calculation) The actual yield (amount produced) of a reaction is usually less than the maximum expected (theoretical yield).

Section 9.3 Limiting Reactants and Percent Yield Percent Yield Consider the following problem: A 2.50 g sample of Sodium bicarbonate was reacted with excess hydrochloric acid. What is the expected yield of NaCl and what is the percent yield if the actual yield was 1.56 g of NaCl. Remember, the balanced reaction is: NaHCO 3 + HCl  NaCl + CO 2 + H 2 O

Section 9.3 Limiting Reactants and Percent Yield Percent Yield Reasons for % yield < 100 % The reactants are not pure. Reactants are involved in “side” reactions Products are lost in transfer, isolation, or purification steps. Can the % yield be more than 100%??? Theoretically…..NO! (violates the Law of Conservation of Mass)

Section 9.3 Limiting Reactants and Percent Yield Objective Define the terms limiting reactant and excess reactant. Identify the limiting reactant in a balanced equation.

Section 9.3 Limiting Reactants and Percent Yield Remember the following problem: You are building model cars. Each car has four tires, two doors, and one body. If you have 16 tires, 10 doors, and 7 car bodies, how many model cars can you build? What part limits the number of model cars that can be built?

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 A. The Concept of Limiting Reactants Limiting Reactant – reactant that limits the amount of product that can form; it is the reactant that gets used up in a reaction Excess Reactant – reactant that is left over at the end of a reaction

Section 9.3 Limiting Reactants and Percent Yield Finding the Limiting Reactant N 2 H 4 (l) + 2 H 2 O 2 (l)  N 2 (g) + 4 H 2 O (l) Which is the limiting reactant when mol of N 2 H 4 is mixed with mol of H 2 O 2 ? A given amount of a reactant is used to determine the required amount of the other reactant. That amount is then compared to the actual amount.

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) –Limiting reactant is the reactant that runs out first. H 2

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

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