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Limiting Reactants and Percent Yield

Limiting Reactants and Percent Yield. Notes 9.3 Chemistry. The concept of Limiting Reactants.

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Limiting Reactants and Percent Yield

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  1. Limiting Reactants and Percent Yield Notes 9.3 Chemistry

  2. The concept of Limiting Reactants To determine how much product can be formed from a given mixture of reactants, we have to look for the reactant that is limiting- the one that runs out first and thus limits the amount of product that can form The reactant that runs out first and thus limits the amounts of products that can form is called the limiting reactant

  3. Calculations Involving a Limiting Reactant Suppose that 25.0 kg of nitrogen gas and 5.00 kg of hydrogen gas are mixed and reacted to form ammonia. Calculate the mass of ammonia produced when this reaction is run to completion. N₂ (g) + 3 H₂ (g)  2 NH₃ (g)

  4. Con’t 2.50 x 104 g N₂ x 1 mol N₂ x 2 mol NH3 x 17 g NH3= 30357 g NH3 28.02 g N₂ 1 mol N2 1 mol NH3 5.00 x 103 g H₂ x 1 mol H₂ x 2 mols NH3 x 17 g NH3= 28333g NH3 2.016 g H₂ 3 mols H2 1 mol NH3 H2 is the limiting reactant since it produces the least amount of product.

  5. Percent Yield Theoretical yield- the maximum amount of a given product that can be formed when the limiting reactant is completely consumed (stoichiometry problem) Actual yield is actually the amount obtained in a lab ( will be given to you in the problem) Actual yield x 100 = % percent yield Theoretical yield

  6. example Methanol can be produced by the reactant between carbon monoxide and hydrogen. Let’s consider this process again. Suppose 68.5kg of CO is reacted with 8.60 kg of H₂. Calculate the theoretical yield of methanol If 3.57 x 104 g of CH₃OH is actually produced, what is the percent yield of methanol? 2 H₂ (g) + CO (g)  CH₃OH (l)

  7. Con’t (figure the limiting reactant first) 6.85 x 104 g CO x 1 mol CO x 1 mol CH3OH x 32 g CH3OH =78285 g CH3OH 28.01 g CO 1 mol CO 1 mol CH3OH 8.6 x 103 g H₂ x 1 mol H₂ x 1 mol CH3OH x 32 g CH3OH =68800 g CH3OH 2.016 g H₂ 2 mols H2 1 mol CH3OH H₂ is the limiting reactant because it produces the least amount of product.

  8. Con’t Actual yield x 100% = percent yield Theoretical yield 3.57 x 104 g CH₃OH x 100% = 52.0% yield 6.88 x 104 g CH₃OH

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