Transcript Limiting and Excess Reactants

Percentage Yield
Limiting Reactant – The substance that controls
the quantity of product that can form in a
chemical reaction
 Excess Reactant – The substance that is NOT
used up completely in the reaction
 Yield – The mass of product formed
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 Theoretic – assuming no loss or error, the
mathematical calculation of the mass of product
formed
 Actual – the measured amount of the product from a
reaction
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We use stoichiometry to determine:
 Limiting Reactant
 Excess Reactant
 Theoretic Yield
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The Limiting reactant will form the LEAST
amount of product.
The Excess reactant will form the MOST
amount of the product.
We can determine these using stoichiometry
if we know how much mass (or how many
moles) we have of each reactant.
Zn + 2HCl  ZnCl2 + H2
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If you combine 0.23 mol Zn and 0.60 mol HCl,
would they react completely?
In other words, will they produce the same
amount of product, or will one produce more
ZnCl2 than the other?
PCl3 + 3H2O  H3PO3 + 3HCl

Determine the limiting and excess reactants
in this equation if you have 75.0 g PCl3 and
75.0 g H2O.
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How about 1.o mol of PCl3 and 50.0 g of H2O?
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The theoretic yield is what you determined
when you determined the limiting reactant.
This is the most product that can be
produced in ideal circumstances.
There will be instances when you will have
more product than you should. Why might
that be?
There will be instances when you will have
less product. Why??
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Actual yield is determined by measurement
after the reaction is complete.
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This is a ratio of the actual yield of a reaction
to its theoretic yield.
This ratio determines the efficiency of the
reaction.
Percent Yield =
Actual Yield
Theoretic Yield
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If the theoretic yield for a reaction is 738 g,
and the actual yield is 591 g, what is the
percentage yield?
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How many grams of CH3COOC5H11 should
form if 4808 g are theoretically possible, and
the percentage yield is 80.5%?
N2 + 3H2  2NH3

14.0 g N2 react with 3.15 g H2 to give an actual
yield of 14.5 g of NH3. Determine the limiting
reactant and the percentage yield for this
reaction.
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A chemist reacts 8.85 g of iron with an excess
of hydrogen chloride to form hydrogen gas
and iron (II) chloride. Calculate the
theoretical yield and the percentage yield of
hydrogen if 0.27 g of H2 are collected.