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1 Percent Yield and Limiting Reactants Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Edited by bbg.

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Presentation on theme: "1 Percent Yield and Limiting Reactants Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Edited by bbg."— Presentation transcript:

1 1 Percent Yield and Limiting Reactants Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Edited by bbg

2 2 Theoretical, Actual, and Percent Yield Theoretical yield The maximum amount of product, which is calculated using the balanced equation. Actual yield The amount of product obtained when the reaction takes place. Percent yield The ratio of actual yield to theoretical yield. percent yield = actual yield (g) x 100 theoretical yield (g)

3 3 Guide to Calculations for Percent Yield Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

4 4 You prepared cookie dough to make 5 dozen cookies. The phone rings and you answer. While you talk, a sheet of 12 cookies burn and you throw them out. The rest of the cookies are okay. What is the percent yield of edible cookies? Theoretical yield Theoretical yield 60 cookies possible Actual yield Actual yield 48 cookies to eat Percent yield80% yield Percent yield 48 cookies x 100 = 80% yield 60 cookies Calculating Percent Yield

5 5 Learning Check Without proper ventilation and limited oxygen, the reaction of carbon and oxygen produces carbon monoxide. 2C(g) + O 2 (g) 2CO(g) What is the percent yield if 40.0 g CO are produced when 30.0 g O 2 are used? 1) 25.0% 2) 75.0% 3) 76.2%

6 6 Solution 3) 76.2 % yield theoretical yield of CO 30.0 g O 2 x 1 mole O 2 x 2 moles CO x 28.0 g CO 32.0 g O 2 1 mole O 2 1 mole CO = 52.5 g CO (theoretical) percent yield 76.2 % yield 40.0 g CO (actual) x 100 = 76.2 % yield 52.5 g CO (theoretical)

7 7 Learning Check When N 2 and 5.00 g H 2 are mixed, the reaction produces 16.0 g NH 3. What is the percent yield for the reaction? N 2 (g) + 3H 2 (g) 2NH 3 (g) 1) 31.3 % 2) 56.5 % 3) 80.0 %

8 8 Solution 2) 56.5 % N 2 (g) + 3H 2 (g) 2NH 3 (g) 5.00 g H 2 x 1 mole H 2 x 2 moles NH 3 x 17.0 g NH 3 2.02 g H 2 3 moles H 2 1 mole NH 3 = 28.2 g NH 3 (theoretical) Percent yield56.7 % Percent yield = 16.0 g NH 3 x 100 = 56.7 % 28.2 g NH 3

9 9 Limiting Reactant limiting reactant A limiting reactant in a chemical reaction is the substance that Is used up first. Limits the amount of product that can form and stops the reaction.

10 10 Reacting Amounts In a table setting, there is 1plate, 1 fork, 1 knife, and 1 spoon. How many table settings are possible from 5 plates, 6 forks, 4 spoons, and 7 knives? What is the limiting item? Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

11 11 Reacting Amounts Only 4 place settings are possible. Initially Used Left over Plates 5 41 Forks 6 42 Spoons 4 4 0 Knives 7 4 3 The limiting item is the spoon. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

12 12 Example of An Everyday Limiting Reactant How many peanut butter sandwiches could be made from 8 slices of bread and 1 jar of peanut butter? With 8 slices of bread, only 4 sandwiches could be made. The bread is the limiting item.

13 13 Example of An Everyday Limiting Reactant How many peanut butter sandwiches could be made from 8 slices bread and 1 tablespoon of peanut butter? peanut butter With 1 tablespoon of peanut butter, only 1 sandwich could be made. The peanut butter is the limiting item.

14 14 Guide to Calculating Product from a Limiting Reactant Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

15 15 Limiting Reactant When 4.00 moles H 2 is mixed with 2.00 moles Cl 2,how many moles of HCl can form? H 2 (g) + Cl(g) 2HCl (g) 4.00 moles 2.00 moles ??? moles Calculate the moles of product that each reactant, H 2 and Cl 2, could produce. The limiting reactant is the one that produces the smallest amount of product.

16 16 Limiting Reactant HCl from H 2 4.00 moles H 2 x 2 moles HCl = 8.00 moles HCl 1 moles H 2 (not possible) HCl from Cl 2 2.00 moles Cl 2 x 2 moles HCl = 4.00 moles HCl 1 mole Cl 2 (smaller number of moles, Cl 2 will be used up first) The limiting reactant is Cl 2 because it is used up first. Thus Cl 2 produces the smaller number of moles of HCl.

17 17 Check Calculations InitiallyH 2 4.00 moles Cl 2 2.00 moles 2HCl 0 mole Reacted/ Formed -2.00 moles +4.00 moles Left after reaction 2.00 moles Excess 0 mole Limiting 4.00 moles

18 18 Limiting Reactants Using Mass If 4.80 moles Ca are mixed with 2.00 moles N 2, which is the limiting reactant? 3Ca(s) + N 2 (g) Ca 3 N 2 (s)moles of Ca 3 N 2 from Ca 4.80 moles Ca x 1 mole Ca 3 N 2 = 1.60 moles Ca 3 N 2 3 moles Ca (Ca is used up) moles of Ca 3 N 2 from N 2 2.00 moles N 2 x 1 mole Ca 3 N 2 = 2.00 moles Ca 3 N 2 1 mole N 2 (not possible) Ca Ca is used up when 1.60 mole Ca 3 N 2 forms. Thus, Ca is the limiting reactant.

19 19 Limiting Reactants Using Mass Calculate the mass of water produced when 8.00 g H 2 and 24.0 g O 2 react? 2H 2 (g) + O 2 (g) 2H 2 O(l)

20 20 Limiting Reactants Using Mass Moles H 2 O from H 2 : 8.00 g H 2 x 1 mole H 2 x 2 moles H 2 O = 3.97 moles H 2 O 2.02 g H 2 2 moles H 2 (not possible) Moles H 2 O from O 2 : 24.0 g O 2 x 1 mole O 2 x 2 moles H 2 O = 1.50 moles H 2 O 32.0 g O 2 1 mole O 2 O 2 is limiting The maximum amount of product is 1.50 moles H 2 O, which is converted to grams. 27.0 g H 2 O 1.50 moles H 2 O x 18.0 g H 2 O = 27.0 g H 2 O 1 mole H 2 O


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