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Limiting Reagent and Percent Yield in Chemical Reactions

Explore the concept of limiting reagents and percent yield in chemical reactions through experiments and calculations. Understand the effect of insufficient reactants on product formation and measure the efficiency of reactions through percent yield calculations.

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Limiting Reagent and Percent Yield in Chemical Reactions

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  1. Drill • The complete combustion of ethanol produces carbon dioxide and water according to the following chemical equation: C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) • How many moles of oxygen are necessary to produce 18.0 moles of carbon dioxide?

  2. Objective • The student will be able to: • Complete an experiment in order to illustrate the concept of a limiting reagent in a chemical reaction.

  3. SAT/HSA Enrichment • 175.6g of NH3 gas is stored at STP. The volume of the gas at those conditions is… • 10.32 liters • 22.40 liters • 175.6 liters • 231.4 liters • 3933 liters

  4. Small Scale-Lab • Analysis of Baking Soda • Purpose: To determine the mass of sodium hydrogen carbonate in a sample of baking soda using stoichiometry. 30 MIN

  5. Limiting Reagent and Percent Yield

  6. Limiting Reagent and Percent Yield • If a carpenter had two tabletops and seven table legs, he could only build one four-legged table. The number of table legs is the limiting factor in the construction of four-legged tables. Similarly, in chemistry, the amount of product made in a chemical reaction may be limited by the amount of one or more of the reactants.

  7. Limiting and Excess Reagents • In a chemical reaction, an insufficient quantity of any of the reactants will limit the amount of product that forms. • The limiting reagent is the reagent that determines the amount of product that can be formed by a reaction.

  8. Limiting and Excess Reagents • In the reaction of nitrogen and hydrogen, hydrogen is the limiting reagent. Nitrogen is the reagent that is not completely used up in the reaction. The reagent that is not used up is called the excess reagent.

  9. Limiting and Excess Reagents The Chemical Equation for the Preparation of Ammonia

  10. SAMPLE PROBLEM

  11. SAMPLE PROBLEM

  12. SAMPLE PROBLEM

  13. SAMPLE PROBLEM

  14. SAMPLE PROBLEM 2

  15. SAMPLE PROBLEM 2

  16. SAMPLE PROBLM 2

  17. Percent Yield • The percent yield is a measure of the efficiency of a reaction carried out in the laboratory. • A batting average is actually a percent yield.

  18. Percent Yield • The theoretical yield is the maximum amount of product that could be formed from given amounts of reactants. • In contrast, the amount of product that actually forms when the reaction is carried out in the laboratory is called the actual yield. • The percent yield is the ratio of the actual yield to the theoretical yield expressed as a percent.

  19. SAMPLE PROBLEM 3

  20. SAMPLE PROBLEM 3

  21. SAMPLE PROBLEM 3

  22. Quick Lab • Limiting Reagents • Purpose: To illustrate the concept of a limiting reagent in a chemical reaction.

  23. Summary • Did we accomplish the objective? Explain. • In a chemical reaction, how does an insufficient quantity of a reactant affect the amount of a product formed? • Insufficient quantity of any reactants will limit the amount of product. • How can you gauge the efficiency of a reaction carried out in the lab? • Can be measured by calculating the percent yield.

  24. Homework • Read the Percent Yield of a Salt Lab • Pre-Lab Quiz next class!

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