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Understanding Limiting Reactants and Percent Yield in Chemical Reactions

In this lesson, we explore the concepts of limiting reactants and percent yield in chemical reactions. Using the reaction between calcium metal and hydrochloric acid as an example, we determine the limiting reactant when 7 moles of calcium react with 16 moles of hydrochloric acid. We also delve into the definitions of theoretical yield and actual yield, emphasizing how actual yields are often lower due to side reactions and purification losses. Through sample problems, we learn how to calculate percent yield, an essential measure of reaction efficiency.

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Understanding Limiting Reactants and Percent Yield in Chemical Reactions

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  1. MondayFebruary 11, 2013 (Discussion and WS – Percent Yield)

  2. Bell RingerMonday, 2-11-13 Calcium metal reacts with hydrochloric acid. If 7 mol of calcium are exposed to 16 mol of hydrochloric acid, which is the limiting reactant? • L • E • Ca + HCl æ CaCl2 + H2 • 2 • Have: • 7 moles • 16 moles • Need: • 7 moles • 14 moles

  3. Announcements Happy Clean Out Your Computer Day!

  4. Announcements I will be available after school today from 4:45 until 5:15.

  5. Percent Yield • The amounts of products calculated in the stoichiometric problems in this chapter so far represent theoretical yields. • The theoretical yield is themaximum amount of product that can be produced from a given amount of reactant. • In most chemical reactions, the amount of product obtained is less than the theoretical yield.

  6. Percent Yield • There are many reasons for this. • Some of the reactant may be used in competing side reactions that reduce the amount of the desired product. • Also, once a product is formed, it often is usually collected in impure form, and some of the product is often lost during the purification process.

  7. Percent Yield • The measured amount of a product obtained from a reaction is called the actual yield of that product. • Chemists are usually interested in the efficiency of a reaction. • The efficiency is expressed by comparing the actual and theoretical yields. • The percent yield is theratio of the actual yield to the theoretical yield, multiplied by 100.

  8. Percent Yield

  9. Percent Yield Sample Problem A chemist runs a reaction based upon the following equation. PCl3 + Cl2æ PCl5 (AB) The chemist starts with 50 grams of PCl3 and produces 73 grams of PCl5. What was the chemist’s percent yield for this reaction? % YIELD = 73 grams 96.4 % = X 100 75.7 grams Determined from a mass to mass stoichiometric calculation

  10. Percent Yield Sample Problem Methanol (CH3OH) can be produced through the reaction of CO and H2. CO + H2æ CH3OH If 100 grams of H2 reacts to produce 750 grams of CH3OH, what is the percent yield for this reaction? • 2 % YIELD = 750 grams 93.8 % = X 100 800 grams Determined from a mass to mass stoichiometric calculation

  11. Worksheet Percent Yield

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