Chemistry 12.3 “Limiting Reagent and Percent Yield”

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Chemistry 12.3 “Limiting Reagent and Percent Yield”

I. Limiting / Excess Reactants A. Limiting Reactant 1. Def – the substance you run out of in a reaction. a. “It is limiting” B. Excess Reactant 1. Def – the substance that has extra/leftover in a reaction. a. “It is in abundance”

C. Ex: N 2 + 3H 2  2NH 3 -if I have 3 moles of N 2 and 8 moles of H 2, which will be my limiting reactant? -what will be my excess reactant? H2H2 N2N2

D. Question: Sodium chloride can be prepared by the reaction of sodium metal with chlorine gas. 2 Na + Cl 2  2 NaCl Suppose the 6.7 mol Na reacts with 3.2 mol of Cl 2. What is the limiting reactant? How much salt can be made? GivenMole Ratio Amount Produced

6.7 mol Na x 1 mol Cl 2 2 mol Na = 3.35 mol Cl 2 How much chlorine do we have? 3.2 mol Cl 2 Limiting Reactant = Excess Reactant = How much salt? = chlorine sodium 6.40 mol NaCl

In Class Assignment Copper plus sulfur produce copper (I) sulfide. a. What is the limiting reactant when 80.0 g of Cu (I) react with 25.0 g of sulfur? b. What is the total amount in grams of copper (I) sulfide that can be made? a. Limiting reactant = Copper b. Amount produced = 100. grams of Cu 2 S

II. Percent Yield A. Calculating Percent Yield 1. Formula Percent Yield = 2. parts… a. Theoretical yield = maximum product that could be made. Comes from the chemical formula. b. Actual yield = the amount of product that is made in a chemical reaction. c. Can never be more than 100% actual yield Theoretical yield X 100

-why less than 100%? 1. impure reactants 2. side reactions 3. loss of products (transferring between containers)