how much can i make? maximizing chemical quantities
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How much can I make? Maximizing Chemical Quantities. Limiting and Excess Reactants Percent Yield. What is a limiting reactant?. Limiting Reactant - reactant in a chemical reaction that limits the amount of product that can be formed - PowerPoint PPT PresentationTRANSCRIPT
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How much can I make?Maximizing Chemical Quantities
Limiting and Excess ReactantsPercent Yield
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What is a limiting reactant?• Limiting Reactant - reactant in a chemical reaction
that limits the amount of product that can be formed
• The reaction will stop once all of the limiting reactant is consumed.
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What is an excess reactant?• Excess Reactant - reactant in a chemical reaction
that remains when a reaction stops• The excess reactant remains because there is
nothing to react with it!
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How many cars can be made?
No matter how many tires there are, if there are only 8 car bodies, then only 8 cars can be made.
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Example #1: Copper metal reacts with sulfur to form copper (I) sulfide
according to the balanced equation. _____ Cu + ____ S _____ Cu2S
What is the limiting reactant when 80 g Cu reacts with 25 g S?
80 g Cu x _________ = mol of Cu
25 g of S x _______ = mol of S
2 1 1
1 mol Cu
63.5 g Cu
1 mol S32.1 g S
1.26
1.09
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Example #1: 2 Cu + 1 S 1 Cu2S
• What is the mole ratio of Cu to ? ____ Cu : ____ S• mol of Cu x ___________ =
mol of S
Translation: • I only need mol of S to fully react with copper. • But I was given ________ mol of S. • Excess = Sulfur Limiting = Copper
2 11.26
2 mol Cu1 mol S 0.63
0.631.09
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What’s the max amount of product that I can yield?
• Use Stoichiometry to determine the max amount of product that can be formed.
1.26 mol Cu x _______ x ________ = 2 mol Cu
1 mol Cu2S
1 mol Cu2S
159.1 g Cu2S 100 g Cu2S
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Theoretically vs. Actually
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Percent Yield
• Theoretical Yield = maximum amount of product that could be formed from a given amount of reactants
• Actual Yield = amount actually formed when a reaction is carried out
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Why don’t reactions always go to completion?
• purity of reactants• loss of product formed
during filtration• competing reactions• measurement error
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Theoretical Yield Example• What is the theoretical yield of CaO if 24.8 g of
CaCO3 is heated? _____ CaCO3 _____ CaO + ______ CO2
24. 8 g CaCO3 x ________ x _________ x ________ = 13.9 g CaO
• Theoretical Yield = 13.9 g CaO
100.1 g CaCO3
1 mol CaCO3
1 mol CaCO3
1 mol CaO
1 mol CaO
56 g CaO
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Percent Yield Example• What is the percent yield if 13.1 g of CaO was
actually produced when 24.8 g of CaCO3 was heated?
• % Yield= 13.1 g x 100 = 94.2 % 13.9 g