LIMITING REACTANT

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LIMITING REACTANT

• Actual and Theoretical Yields, and the Percent
  Yield

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LIMITING REACTANT

• IMPORTANCE
• Calculations of limiting reactant, theoretical
  and percent yield are central to chemistry
  because they bring quantitative understanding to
  chemical reactions
• These calculations are used in both, General and
  Organic Chemistry

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LIMITING REACTANT LESSON PLAN

• OBJECTIVES
• Acquire the skills necessary to recognize a
  limiting reactant problem
• Definitions
• Three methods used to determine the limiting
  reactant
• Theoretical yield and the percent yield
  calculations

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DEFINITIONS

• LIMITING REACTANT
• Completely consumed in a chemical reaction
• Determines the amount of product formed
• The reactant that produces the least amount of
  product

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DEFINITIONS

• THEORETICAL YIELD
• The amount of product that can be made based on
  the amount of the limiting reactant
• ACTUAL YIELD
• The amount of product actually or experimentally
  produced
• THE PERCENT YIELD
• yield (actual/theoretical)x100

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METHODS USED TO DETERMINE THE LIMITING REACTANT

• Calculate the moles needed of each reactant and
  compare with the moles given
• II. Divide the moles of each reactant by its
  stoichiometric coefficient and then compare them
• Calculate the moles of product produced by each
  reactant and compare them

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Limiting Reactant

• 1N2(g) 3H2(g) ? 2NH3(g)
• Given 3.0 mole 6.0 mole
• I. Calculate the amount of reactant needed
• 3.0 mol N2 x 3mol H2 9.0 mol H2 needed
• 1mol N2
• 6.0 mole H2 given lt 9.0 mol H2needed
• H2 is the Limiting Reactant

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Limiting Reactant

• 1N2(g) 3H2(g) ? 2NH3(g)
• Given 3.0 mole 6.0 mole
• I. Calculate the amount of reactant needed
• 6.0 mol H2 x 1mol N2 2.0 mol N2 needed
• 3mol H2
  
• 3.0 mole N2 given gt 2.0 mol N2needed
• N2 is in excess H2 is the Limiting Reactant

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Limiting Reactant

• 1N2(g) 3H2(g) ? 2NH3(g)
• Given 3.0 mole 6.0 mole
• II. Divide the moles of each reactant by its
  stoichiometric coefficient
• 3.0 mol N2 3.0mol N2 6.0 mol H2
  2.0mol H2
• 1.0 mol N2 3.0 mol H2
• The reactant present in smaller
  amount is the L.R. ---- H2 (2.0 mol is the
  change)

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Limiting Reactant

• 1N2(g) 3H2(g) ? 2NH3(g)
• Given 3.0 mole 6.0 mole
• III. Calculate the amount of product produced by
  each reactant
• 3.0 mol N2 x 2 mol NH3 6.0 mol NH3
• 1 mol N2
• 6.0 mol H2 x 2 mol NH3 4.0 mol NH3
  (theoretical yield)
• 3 mol H2
• The reactant that produces the least amount of
  product is the L.R.------- H2

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Excess Reactant

• How much of the excess reactant reacted and how
  much is left unreacted?
• 1N2(g) 3H2(g) ? 2NH3(g)
• Given 3.0 mole 6.0 mole
• 6.0 mol H2 x 1 mol N2 2.0 mol N2 reacted
• 3 mol H2
• Unreacted N2initial(given) reacted
• Unreacted N2 3.0mol - 2.0 mol 1.0 mol N2

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1N2(g) 3H2(g) ? 2NH3(g)
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1N2(g) 3H2(g) ? 2NH3(g)

• Initial 3.0 mol 6.0 mol 0.0
  mol
• Change - 2.0molx1 -2.0molx3 2.0molx2
• - 2.0mol -6.0mol 4.0
  mol
• Final 1.0 mol 0.0 mol 4.0
  mol
• excess L.R.
  Theoretical yield

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Percent Yield Calculation

• Knowing that the theoretical yield of ammonia is
  4.0 mol and the actual (experimental) yield of
  ammonia is 55.38 g, calculate the yield of NH3.
  N2(g) 3H2(g) ? 2NH3(g)
• 4.0 mol NH3 x 17.00 g NH3 68.00 g NH3
• 1mol NH3
• yield ( 55.38 g/68.00 g)x100 81.44