9.2 Chemical Calcualtions. Chapter 9 Stoichiometry. 9.1 The Arithmetic of Equations. 9.2 Chemical Calculations. 9.3 Limiting Reagent and Percent Yield

Transcription

1 9.2 Chemical Calcualtions Chapter 9 Stoichiometry 9.1 The Arithmetic of Equations 9.2 Chemical Calculations 9.3 Limiting Reagent and Percent Yield 1 Copyright Pearson Education, Inc., or its affiliates. All Rights Reserved.

2 9.3 Limiting Reagent and Percent Yield

3 objectives Identify 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.,

4 vocabulary limiting reagent excess reagent theoretical yield actual yield

5 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.

6 6 limiting reagent the amount of product is determined by the limiting reagent.

7 7 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?

8 8 9.8 sample known: moles of sodium=6.70 Na moles of chlorine= 3.20 Cl2 2 mo of Na= 1 mol Cl2 unknown: limiting reagent=?

9 9 9.8 sample 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.

10 10 knowns amount of limiting reagent= 3.2 mol Cl2 1 mol Cl2= 2 mol NaCl unknowns moles of sodium chloride=? mol NaCl

11 sample knowns amount of limiting reagent=3.20 mol Cl2 1mol Cl2 = 2 mol NaCl (from balanced equation) unknowns moles of sodium chloride=? mol NaCl

12 sample knowns amount of limiting reagent=3.20 mol Cl2 1mol Cl2 = 2 mol NaCl (from balanced equation) unknowns moles of sodium chloride=? mol NaCl

13 sample solve for the unknown

14 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?

15 sample Do 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.

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

17 sample 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? known unknown mass of copper 80g Cu limiting reagent mass of Sulfur 25g S 2 mol Cu= 1 mol S (from balanced equation)

18 sample 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? limiting reagent

19 sample 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? 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.

20 sample known limiting reagent=1.26 mol Cu 2 mol Cu=1 mol unknown mass of 1 mol = g 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?

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

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

23 23 homework problems a) identify the limiting reagent b) calculate the number of moles and grams of water produced

24 24 homework problems

25 25 Theoretical Yield: the maximum amount of product that can be formed from the given reactants obtained by calculations

26 26 Actual Yield: The amount of product that actually forms in the laboratory. The actual yield is often less than the theoretical yield.

27 27 Percent Yield: the ratio of the actual yield to the theoretical yield expressed as a percent.

28 28

29 sample Calcium carbonate is decomposed by heating as shown in the equation 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?

30 sample Calcium carbonate is decomposed by heating as shown in the equation 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 knowns 1 mol CaCO3=1mol CaO (balanced equation) 1mol CaCO3= g CaCO3 (mass) 1 mol CaO=56.1 g CaO (molar mass) unknowns theoretical yield of calcium oxide=?

31 sample knowns actual yield= 13.1 CaO theoretical yield= 13.9 g CaO (from the first calculation) unknowns percent yield?

32 sample