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# Lecture 12.3- Limiting Reagents and Percent Yield

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Section 12.3 Lecture for Honors Chemistry …

Section 12.3 Lecture for Honors Chemistry
Slides 1-7 are for Prep as well

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• A batting average is actually a percent yield.
• ### Transcript

• 1. Bellwork- Make 1cup of water H 2 + O 2 ïƒ  H 2 O How many liters of H 2 gas and O 2 gas at STP are required to make a cup of water? One cup (240mL) has a mass of 240g for pure water. 240g H 2 O x 1mol = 13.3mol H 2 O 18g 13.3 mol H 2 O x 13.3 mol H 2 O x 2 2 2 moles H 2 2 moles H 2 O 1 mole O 2 . 2 moles H 2 O = 13.3mol H 2 = 6.67mol O 2 x 22.4L/mol = 299L H 2 x 22.4L/mol = 149L O 2
• 2. Limiting Reagent and Percent Yield
• If a carpenter had two tabletops and seven table legs, he cou ld only build one four-legged table.
• The number of table legs is the limiting factor.
• 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.
• 3.
• 2 H 2 + O 2 ï‚® 2H 2 O
• When reactants combine in their stoichiometric ratio (a.k.a. mole ratio ), both reactants will be completely used.
• In any other ratio, one of the reactants will be used up and the other will have some left over.
• 4.
• 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.
• 5.
• N 2 + 3H 2 ïƒ  2NH 3
• Youâ€™ve got 2mole N 2 3mol H 2
• How much NH 3 can you make?
• What is the limiting reactant?
• 6.
• N 2 + 3H 2 ïƒ  2NH 3
• Youâ€™ve got 2mole N 2 3mol H 2
• How much NH 3 can you make? Only 2 moles
• What is the limiting reactant? Hydrogen, because there is not enough H 2 to react with the 2nd mole of N 2.
• 7.
• 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 .
• N 2 + 3H 2 ïƒ  2NH 3
• Youâ€™ve got 2mole N 2 3mol H 2
• 8. 12.7
• 9. 12.7
• 10. 12.7
• 11. 12.7
• 12. for Sample Problem 12.7
• 13. 12.8Q
• 14. 12.8
• 15. 12.8
• 16. 12.8
• 17. for Sample Problem 12.8
• 18.
• 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.
• 19.
• 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 .
comes from stoichiometry comes from the lab
• 20.
• The percent yield is the ratio of the actual yield to the theoretical yield expressed as a percent.
What yo u get in the lab What you get mathematically
• 21. The actual yield is often lower than the theoretical yield because not all reactions go to completion. The actual yield should never be higher than your theoretical yield.
• 22. 12.9
• 23. 12.9
• 24. 12.9
• 25. 12.9
• 26. 12.10
• 27. 12.10
• 28. 12.10
• 29. 12.10
• 30. for Sample Problem 12.10
• 31. 12.3 Section Quiz.
• 1. In the reaction 3NO 2 + H 2 O ï‚® 2HNO 3 + NO, how many grams of HNO 3 can form when 1.00 g of NO 2 and 2.25 g of H 2 O are allowed to react?
• 0.913 g
• 0.667 g
• 15.7 g
• 1.37 g
• 32. 12.3 Section Quiz.
• 2. How many grams of H 2 O can be formed from 24.0 g O 2 and 6.00 g H 2 ?
• 30.0 g
• 27.0 g
• 54.0 g
• 13.5 g
• 33.
• 3. Octane burns according to the following equation.
• 2C 8 H 18 + 25O 2 ï‚® 16CO 2 + 18H 2 O
• What is the percent yield if 14.6 g of CO 2 are produced when 5.00 g of C 8 H 18 are burned?
• 106%
• 94.8%
• 34.2%
• 62.5%
12.3 Section Quiz.