# Percent Yield and Limiting Reactants

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Percent Yield and Limiting Reactants
Using Reaction Stoichiometry

Percent Yield % Yield= Actual Yield / Theoretical Yield x 100
Actual Yield- from a lab (what was actually produced) Theoretical Yield- from a reaction stoichiometry problem (mathematical value… what you should have gotten)

Percent Yield Practice
PbS + O2  PbO + SO2 Balance the equation above. What is the theoretical yield of PbO if 200.0g of PbS is reacted? If 170.0g of PbO is obtained in a chemical reaction, what is the percent yield?

More practice… Upon heating, solid calcium carbonate decomposes to form solid calcium oxide and carbon dioxide gas. Write the complete balanced chemical reaction for the reaction. Determine the percent yield if 235.0g of calcium carbonate is heated and 97.5g of carbon dioxide is collected.

Limiting Reactants Limiting Reactant- the reactant (reagent) that produces the fewest moles of product. Reaction can only form the amount of product “allowed” by the limiting reactant.

Limiting Reactant Steps
Balance the Equation Use mole ratios to find the moles of a product formed by each reactant (using the amounts given in the problem) The reactant that makes the smallest number of moles of product is the limiting reactant. The other is the excess reactant. The smallest number of moles produced will be the actual amount of product formed in the reaction. To find excess reactant remaining: Subtract the two amounts of product formed (from step #2 above) and use mole ratios convert back to the reactant.

Limiting Reactant Practice
H O2 → H2O If 12.2 mol H2 and 8.4 mol O2 react… What is the limiting reactant/reagent? The excess reactant?  How many moles of water are produced?   How many grams of water are produced? How many moles of excess reactant remain?