Chapter 9valverdescience.pbworks.com/w/file/fetch/64058596/2 27 13 ppt.pdf• suppose that 6.7 mol...

9.2 Chemical Calcualtions

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Chapter 9Stoichiometry

9.1 The Arithmetic of Equations

9.2 Chemical Calculations

9.3 Limiting Reagent and Percent Yield

Wednesday, February 27, 13

9.3 Limiting Reagent and Percent Yield


objectivesIdentify and use limiting reagent in a reaction to calculate the maximum amount of products produced and the amount of excess reagent.Calculate theoretical yield, actual yield, or percent yield given appropriate information.,


vocabularylimiting reagent excess reagenttheoretical yield

actual yield


1.If a carpenter had two table table tops and seven table legs. He would have difficulty building more than one functional table.

2.A similar concept applies in chemistry when knowing the exact amounts of reactants and products in a chemical reaction.


Yirah Valverde, M. Ed.

limiting reagent• the amount of product is determined by the limiting reagent.

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sample 9.8• sodium chloride can be prepared by the

reaction of sodium metal with chlorine gas.

• suppose that 6.7 mol Na react with 3.20 mol Cl2

• what is the limiting reagent?• how many moles of NaCl are produced?

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9.8 sample

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known:moles of sodium=6.70 Namoles of chlorine= 3.20 Cl22 mo of Na= 1 mol Cl2

unknown:limiting reagent=?



9.8 sample

9

•This calculation indicates that 3.35mol Cl2 is needed to react with 6.70 mol Na

•Only 3.20 mol of Cl2 is available, Cl becomes the limiting reagent.

•Sodium is in excess.



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knownsamount of limiting reagent= 3.2 mol Cl21 mol Cl2= 2 mol NaCl

unknownsmoles of sodium chloride= ? mol NaCl



9.8 sample

11

knowns• amount of limiting

reagent=3.20 mol Cl2• 1mol Cl2 = 2 mol NaCl (from

balanced equation)

unknowns• moles of sodium chloride= ?

mol NaCl



9.8 sample

12

knowns• amount of limiting

reagent=3.20 mol Cl2• 1mol Cl2 = 2 mol NaCl (from

balanced equation)

unknowns• moles of sodium chloride= ?

mol NaCl



9.8 sample• solve for the unknown

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9.8 sample• suppose that 6.7 mol Na react with 3.20 mol Cl2• solve for the unknown

• This calculation indicates that 3.35mol Cl2 is needed to react with 6.70 mol Na

• Only 3.20 mol of Cl2 is available, Cl becomes the limiting reagent. • Sodium is in excess.

• Do these results make sense?

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9.8 sampleDo these results make sense?

• the ratio of the given moles of sodium chloride to chlorine was greater than 2:1, which is the ratio from the balanced equation, sodium should be in excess and chlorine should be the limiting reagent.

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9.9 sample

• The properties of copper (I) sulfide are very different from the properties of the elements copper and sulfur.

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copper sulfate copper sulfur



9.9 sample

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What is the limiting reagent when 80 g Cu reacts with 25 g S?What is the maximum number of grams of that can be formed?

knownmass of copper 80g Cumass of Sulfur 25g S2 mol Cu= 1 mol S (from balanced equation)

unknownlimiting reagent



9.9 sample

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limiting reagent



9.9 sample

• Comparing the amount of sulfur needed (.630mol S) with the given amount (.779 mol S) indicated that sulfur is in excess. Thus copper is the limiting reagent.

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9.9 sample

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knownlimiting reagent=1.26 mol Cu2 mol Cu=1 mol

1 mol = 159.1 g

unknownmass of




9.9 sample

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the limiting reagent, which was determined in the last step is used to calculate the max amount of Cu2 formed



9.9 sample

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the limiting reagent, which was determined in the last step is used to calculate the max amount of Cu2 formed



homework problems

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a) identify the limiting reagentb) calculate the number of moles and grams of water produced



homework problems

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• Theoretical Yield:–the maximum amount of product that can be formed

from the given reactants–obtained by calculations

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• Actual Yield:–The amount of product that actually forms in the

laboratory.–The actual yield is often less than the theoretical

yield.

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• Percent Yield:–the ratio of the actual yield to the theoretical yield

expressed as a percent.

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9.10 sample

29

Calcium carbonate is decomposed by heating as shown in the equation....

1. what is the theoretical yield of CaO is 24.8g of CaCO3 is heated?2. what is the percent yield if 13.1g CaCO is produced?



9.10 sample

30

Calcium carbonate is decomposed by heating as shown in the equation....

1. what is the theoretical yield of CaO is 24.8g of CaCO3 is heated?2. what is the percent yield if 13.1g CaO is produced? ACTUAL WHEN IS PRODUCED

knowns1 mol CaCO3=1mol CaO (balanced equation)1mol CaCO3= 100.1 g CaCO3 (mass)1 mol CaO=56.1 g CaO (molar mass)

unknownstheoretical yield of calcium oxide=?



9.10 sample

31

knownsactual yield= 13.1 CaOtheoretical yield= 13.9 g CaO (from the first calculation)

unknownspercent yield ?



9.10 sample

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9.3 homework• page # 259 numbers 29-32• no work , no credit. • if you lost your book get the hw from

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