Chapter 7 7 3 Percentage Yield Theoretical Yield

Chapter 7 7. 3: Percentage Yield

Theoretical Yield vs. Actual Yield • Theoretical yield: the amount of product predicted by stoichiometry • Actual yield: the amount of product obtained by experiment

Theoretical Yield vs. Actual Yield • Why do they differ? - Imperfect techniques - Impure reactants - Competing reactions Competing reaction: a reaction that occurs at the same time and involves the same reactants and products. • Chemists have a percentage that is used to express the “success” of a reaction. This percentage is called the percentage yield.

Percentage Yield • Percentage yield: compares the actual yield with theoretical yield % yield= AY x 100 TY

Percentage Yield Sample Problem #1 N 2(g) +3 H 2(g) 2 NH 3(g) When 75. 0 g of nitrogen reacts with sufficient hydrogen, theoretical yield of ammonia is 9. 10 g. If 2. 14 g of ammonia is obtained by experiment, what is the percentage yield of the reaction? (Ans: 23. 5%)

Percentage Yield Sample Problem #2 2 P(s) + 3 Cl 2(g) 2 PCl 3(l) 7. 50 g of chlorine is reacted with excess phosphorus. a) What is theoretical yield of PCl 3 for this reaction? (Ans: 9. 71 g) b) If 1. 25 g of PCl 3 is produced, what is the percentage yield? (Ans: 12. 9%)

Predicting Actual Yield Sample Problem #3 C 3 H 8(g) + 5 O 2 (g) → 3 CO 2 (g) + 4 H 2 O (g) • 37. 0 g of oxygen reacts with excess propane (C 3 H 8). If the percentage yield is 94. 0%, how much carbon dioxide is produced? (Ans: 28. 8 g) – Step 1: find theoretical yield • Answer: 30. 6 g – Step 2: find actual yield • Answer: 28. 8 g

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