Limiting Reagents

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Limiting Reagents
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Example

• Your job is to attach arms on dolls in a doll
  factory. If you have 600 arms and 350 doll
  bodies, how many finished dolls can you make?

What is limiting your production the arms or
the dolls?
What do you have in excess?
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• Reagent reactant in a chem reaction
• Limiting Reagent the reactant that is
  completely consumed. This reactant limits the
  amount of product that is formed.
• Excess Reagent the reactant that is not
  limiting the reaction. There will be leftovers
  of this reactant.

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How to solve for limiting reagent

1. Write the balanced chemical equation
2. Determine the moles of each reactant
3. Determine how many moles of product each reactant
   would make using a mole ratio
4. The reactant that yields less product is the
   limiting reagent.

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Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reagent when 80.0g
Cu reacts with 25.0g S?

1. Write the balanced chemical equation

Cu
S

?
Cu2S
2
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Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reagent when 80.0g
Cu reacts with 25.0g S?

• 2. Determine the moles of each reactant.

1 mole Cu
80.0 g Cu x
1.26 mol Cu
63.55 g Cu
1 mole S
25.0 g S x
.780 mol S
32.06 g S
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Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reagent when 80.0g
Cu reacts with 25.0g S?

• 3. Determine how many moles of product each
  reactant would make using a mole ratio

1 mol Cu2S
1.26 mol Cu x
.630 mol Cu2S
2 mol Cu
1 mol Cu2S
.780 mol S x
.780 mol Cu2S
1 mol S
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Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reagent when 80.0g
Cu reacts with 25.0g S?

• 4. The reactant that yields less product is the
  limiting reagent.

Copper yields .630 mol Cu2S
Sulfur yields .780 mol Cu2S
So Copper is the limiting reagent
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• What is the excess reagent?
• How many moles of Cu2S will be produced?

Sulfur
.630 mol Cu2S
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Amount of Excess?

• In order to determine how much (mass) of excess
  reagents there are, you must figure out what mass
  of the excess reagent got used upthen subtract
  that from the initial mass.

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Amount of Excess?

• Step 1 Start with moles of product formed (from
  limiting reagent).
• Step 2 Convert back to moles of excess reagent.
• Step 3 Convert from moles to mass of excess
  reagent.
• Step 4 Subtract this value from the original
  mass of excess reagent (given in problem)

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• Hydrogen fluoride reacts with aluminum oxide to
  produce aluminum fluoride and water.
• If 60.0g of hydrogen fluoride react with 25.0g of
  aluminum oxide, how many grams of aluminum
  fluoride will be produced?
• Determine the mass of excess reactant remaining.