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How much can I make? Maximizing Chemical Quantities

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

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How much can I make? Maximizing Chemical Quantities

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  1. How much can I make?Maximizing Chemical Quantities Limiting and Excess Reactants Percent Yield

  2. 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.

  3. 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!

  4. 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. 

  5. 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 1.26 1 mol Cu 63.5 g Cu 1.09 1 mol S 32.1 g S

  6. 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 1 1 mol S 0.63 1.26 2 mol Cu 0.63 1.09

  7. 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 Cux _______ x________ = 1 mol Cu2S 159.1 gCu2S 100 gCu2S 2 mol Cu 1 mol Cu2S

  8. Theoretically vs. Actually

  9. 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

  10. Why don’t reactions always go to completion? • purity of reactants • loss of product formed during filtration • competing reactions • measurement error

  11. 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 gCaO • Theoretical Yield = 13.9 gCaO 1 mol CaCO3 1 mol CaO 56 gCaO 100.1 gCaCO3 1 mol CaCO3 1 mol CaO

  12. 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 gx 100 = 94.2 % 13.9 g

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