Assignment: Read 5.6 up to sample (238-9) 1.Define the following terms: yield, theoretical yield, actual yield, percentage yield. 2. Based on your reading, give 4 reasons why the actual yield in a chemical reaction often falls short of the theoretical yield. 3. Read the sample problem on the next slide and try the practice problem on slide number 5 4. When 5.00 g of KClO 3 is heated it decomposes according to the equation: 2KClO 3 2KCl + 3O 2 a) Calculate the theoretical yield of oxygen. b) Give the % yield if 1.78 g of O 2 is produced. c) How much O 2 would be produced if the percentage yield was 78.5%?
Answers 1) Yield : the amount of product Theoretical yield : the amount of product we expect, based on stoichiometric calculations Actual yield : amount of product from a procedure or experiment (this is given in the question) Percent yield : x 100% actual yield theoretical yield 2) • Not all product is recovered (e.g. spattering) • Reactant impurities (e.g. weigh out 100 g of chemical which has 20 g of junk) • A side reaction occurs (e.g. MgO vs. Mg 3 N 2 ) • The reaction does not go to completion
Sample problem Q - What is the % yield of H 2 O if 138 g H 2 O is produced from 16 g H 2 and excess O 2 ? Step 1: write the balanced chemical equation 2H 2 + O 2 2H 2 O Step 2: determine actual and theoretical yield.
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- Fall '17
- Stoichiometry, mol