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13_ Percent Yield

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					PERCENTAGE YIELD
   SECTION 7.3
   THEORETICAL YIELD

• Predicted yield you obtain
  by using the equation
• The amt you “should” obtain
  using stoichiometry
          ACTUAL YIELD
• Amount of product produced in an
  experiment
• Usually actual yield will be lower
  than theoretical yield
                                     UH OH!



• WHY???
  – Human error
  – Experimental error
    Some experimental errors…
• Procedure not followed correctly
• Equipment: broken/not clean
• Reaction not complete
• Other “side reactions” happen at same
  time
• Loss of product
          PERCENT YIELD
• Tells you how CLOSE your actual yield is
  to the theoretical yield (what you should
  have had)

Percent Yield = Actual yield x 100 %
               Theoretical yield

• the closer you are to 100%, the better
  the yield
PERCENT YIELD EXAMPLE 1:
Ex: N2(g) + 3H2(g)    2NH3(g)

When 7.5 x 101 g of N2(g) reacts with
hydrogen, the theoretical yield is 9.10 g.
If only 1.72 g of NH3(g) is obtained in exp,
what is the % yield?
  PERCENT YIELD EXAMPLE:
• Theoretical yield: 9.10 g
• Actual yield: 1.72 g
Percent Yield = Actual yield x 100 %
                  Theoretical yield
Percent yield = 1.72 g x 100%
                  9.10 g
              = 18.9 %
Not very close to 100% (81.1% error!!!!)
Not very good results! 
PERCENT YIELD EXAMPLE 2:
• Ex: N2(g) + 3H2(g)   2NH3(g)

  The actual yield of NH3 is 2.50g, when
  1.5 x 101 g of N2 reacts. What is the
  percent yield?

Hint: Calculate Theoretical yield first! 
HOMEWORK
• Pg 262 # 31, 32
• Pg 264 # 34, 36

				
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posted:2/18/2012
language:English
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