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Percent Yield and Limiting Reactants

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Percent Yield and Limiting Reactants

Using Reaction Stoichiometry

- % 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)

PbS + O2PbO + 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?

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

- 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.

H2+ 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?