# Limiting and Excess Reactants

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Limiting and Excess Reactants

LIMITING REACTANTS LIMIT HOW MUCH OF THE PRODUCT CAN ACTUALLY BE PRODUCED DURING THE REACTION

EXCESS REACTANTS The reactants that are left over when the reaction stops. *When all the limiting reactant is used up

How to find the limiting reactants
Solve each of the problems Which of the problems produces the least amount? This is your Limiting Reactant

Finding the limiting reactants
NaOH + HCl ⇒ H2O + NaCl If there are 25 grams of NaOH, how many grams of H2O will be formed? If there are 16 grams of HCl, how many grams of H2O will be formed? Which is the limiting reactant?______________________

Finding the limiting reactant
2H2 + O2 ⇒ 2H2O Determine the limiting reactant and how much water will be formed from it, if the following is true: 3 grams of H2 and 5 grams of O2

Percent Yield

Percent Yield Actual Yield x 100 = Percent Yield Theoretical Yield
This is a measurement of the accuracy of the chemical reaction. Actual Yield: is the amount of product actually produced, and measured at the end of the reaction. Theoretical Yield: (expected value) is how much product was expected to be produced. This is done by calculating how much should be produced based on the amounts of beginning products. Actual Yield Theoretical Yield x 100 = Percent Yield

How to determine the % yield:
Complete the conversions of both givens Determine which substance is the limiting reactant Use the limiting reactant as the theoretical yield Calculate the percent yield Divide the actual yield by the theoretical yield Multiply by 100 *This determines how accurate your reaction was in percentage

Determining the % Yield:
Mg(OH)2 + 2NaCl ⇒ 2NaOH + MgCl2 Determine the limiting reactant and how many grams of MgCl2 will be formed from it, if there are 4.6 grams of Mg(OH)2 and 7.8 grams of NaCl. What is the % yield if only 5.78g of MgCl2 was collected at the end of the experiment/reaction?

Determining the % Yield:
2H2 + O2 ⇒ 2H2O Determine the limiting reactant and how much water should be formed from it, if 3 grams of H2 and 5 grams of O2. 3g H2 1 mol H2 2 mols H2O 18g H2O = 27g H2O 2g H2 2 mols H mol H2O 5g O2 1 mol O2 2 mols H2O g H2O = 5.625g H2O 32g O2 1 mol O mol H2O What is the percent yield, if the chemist only gathers 3.78g of H2O at the end of the reaction?