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Stoichiometry Mole Ratios Mole Ratios Limiting Reagent Limiting Reagent % Yield % Yield Gas Stoichiometry Gas Stoichiometry.

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Presentation on theme: "Stoichiometry Mole Ratios Mole Ratios Limiting Reagent Limiting Reagent % Yield % Yield Gas Stoichiometry Gas Stoichiometry."— Presentation transcript:

1 Stoichiometry Mole Ratios Mole Ratios Limiting Reagent Limiting Reagent % Yield % Yield Gas Stoichiometry Gas Stoichiometry

2 Stoichiometry Chemistry is often called the science of proportions; Kitchen Chemistry/Recipes Chemistry is often called the science of proportions; Kitchen Chemistry/Recipes Stoichiometry : the study of chemical quantities based on a balanced equation. Stoichiometry : the study of chemical quantities based on a balanced equation.

3 Stoichiometry Measureable and Quantitative relationship between reactants and products Measureable and Quantitative relationship between reactants and products So, a chemical reaction takes place: So, a chemical reaction takes place: Identify: Identify: Classification: Classification: Law of Conservation of Mass: Law of Conservation of Mass:

4 You Must Remember: To BALANCE every equation To BALANCE every equation

5 Remember the mole?? Remember the mole?? Quantities in chemical equations are counted as moles. Quantities in chemical equations are counted as moles.

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7 Chemical Ratios Substances in a balanced equation are always in a given proportion to each other. 1N 2 + 3H 2  2NH 3 The proportions can be written as ratios.

8 Mole Ratios These proportions are called “mole ratios”. These proportions are called “mole ratios”. 1N 2 + 3H 2  2NH 3 For Every There are/is Creating ratio 1N 2 3H 2 1mol N 2 /3mol H 2 1N 2 2NH 3 3H 2 2NH 3 3H 2 N2N2N2N2 2NH 3 1N 2 2NH 3 3H 2

9 Mole Ratios What is the mole ratio found in the balanced equation below? What is the mole ratio found in the balanced equation below? N 2 O 5  NO 2 + O 2

10 The “Given” If 2 moles of N 2 O 5 is reacted, how many moles of NO 2 will be formed? If 2 moles of N 2 O 5 is reacted, how many moles of NO 2 will be formed? There is always a given in a stoichiometry problem that includes There is always a given in a stoichiometry problem that includes  A numeric value (2)  A metric unit (moles)  A substance (N 2 O 5 )

11 Mole-Mole Calculation If 2 moles of N 2 O 5 is reacted, how many moles of NO 2 will be formed? If 2 moles of N 2 O 5 is reacted, how many moles of NO 2 will be formed? 1) 2 mol N 2 O 5 x mole ratio (which one?) 2) 2 mol N 2 O 5 x mol N 2 O 5 (cancel the given) 3) 2 mol N 2 O 5 x mol NO 2 (write what you want) mol N 2 O 5

12 Mole-Mole Calculation 1- Balance the equation 2- Write down your given 3- Use conversion factors to convert moles (use the coefficients here) We call this the Heart of the equation

13 Heart of Every Equation mol unknown = mol given mol given

14 Mole-Mole Calculations _______________________ _______________________ mol given Coef mol coef mol given coef mol unknown

15 Mole-Mass Problem How much (mass) B can be formed from a given number of moles of A? mol A x mol B x g B = g B mol A 1 mol B mol A 1 mol B 1) The mol-mol ratio comes from the equation 2) The mol-mass ratio comes from the periodic table

16 C 3 H 8 + 5O 2  3CO 2 + 4H 2 O 5.4 moles of propane (C 3 H 8 ) is converted into how many moles of carbon dioxide? 5.4 moles of propane (C 3 H 8 ) is converted into how many moles of carbon dioxide?

17 Mole-Mass Calculations ____________________________________ mol given coef mol given coef mol unknown Molar mass (g) 1 mol

18 4NH 3 + 5O 2  6H 2 O + 4NO How many grams of H 2 O are produced if 1.9 mol of NH 3 are combined with excess oxygen? How many grams of H 2 O are produced if 1.9 mol of NH 3 are combined with excess oxygen?

19 Mass-Mole Problem How many moles of B can be formed from a given mass of A? g A x 1 mol A x mol B x = mol B g A mol A 1) The mol-mol ratio comes from the equation 2) The mol-mass ratio comes from the periodic table

20 Mass-Mole Calculations: mol given 1 mol coef mol unknown __________________________________ molar mass coef mol given molar mass coef mol given (g) (g)

21 Fe 2 O 3 + 3CO -> 2Fe + 3CO 2 How many grams of carbon dioxide are produced with 2 moles of iron (3) oxide?

22 Mass-Mass Problem How much (mass) B can be formed from a given mass of A? g A x 1 mol A x mol B x g B = g B g A mol A 1 mol B 1) The mol-mol ratio comes from the equation 2) The mol-mass ratio comes from the periodic table

23 Mass-Mass Calculations: g-given 1 mol coef mol molar mass unknown (g) unknown (g)____________________________________ molar mass coef mol 1 mol molar mass coef mol 1 mol given given

24 Fe 2 O 3 + 3CO -> 2Fe + 3CO 2 How many grams of iron would be produced using 25 grams of iron (3) oxide? How many grams of iron would be produced using 25 grams of iron (3) oxide?

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26 Stoichiometry Mole Ratios Mole Ratios Limiting Reagent-LR Limiting Reagent-LR % Yield % Yield Gas Stoichiometry Gas Stoichiometry

27 Limiting Reagent Limiting reagent = a reactant that limits the amount of product that can be made Limiting reagent = a reactant that limits the amount of product that can be made It can also be thought of as a limiting ingredient

28 Limiting Reagent Recipe: peanut butter and jelly sandwich Recipe: peanut butter and jelly sandwich 2Br + 3Pb + 2Je  1 Sa 2Br + 3Pb + 2Je  1 Sa 3 ingredients necessary to produce one sandwich 3 ingredients necessary to produce one sandwich Could any one of these run Could any one of these run out before the other two?

29 Excess Reagents Excess = there’s extra of this substance Excess = there’s extra of this substance *the substance won’t run out * don’t include this reagent in the calculation If you have 20 loaves of bread, 1 jar of peanut butter and 1 jar of jelly – which ingredient is in excess? If you have 20 loaves of bread, 1 jar of peanut butter and 1 jar of jelly – which ingredient is in excess?

30 Limiting Reagent To determine the limiting reagent, more than one problem must be done To determine the limiting reagent, more than one problem must be done Ex: You have 8 slices of bread and 9 T of peanut butter. Which is the limiting ingredient? (2Br + 3Pb + 2Je  1 Sa) Ex: You have 8 slices of bread and 9 T of peanut butter. Which is the limiting ingredient? (2Br + 3Pb + 2Je  1 Sa) 8 Br x 1Sa = 4 Sa 9 Pb x 1Sa = 3 Sa 2 Br 3Pb 2 Br 3Pb

31 Limiting Reagent The reactant that produces the smallest amount of product is the limiting reagent. The reactant that produces the smallest amount of product is the limiting reagent. 8 Br x 1Sa = 4 Sa 9 Pb x 1Sa = 3 Sa 2 Br 3Pb 2 Br 3Pb Limiting reagent Smaller quantity

32 Uses for Limiting Reactants Nutritional value of food for body Nutritional value of food for body Concentration of pollutants Concentration of pollutants

33 What to do (write these down): Balance equation Balance equation Convert: 1-have to moles Convert: 1-have to moles 2-need to moles 2-need to moles Compare  have : need Compare  have : need One must be > or or < ID the LR ID the LR Excess  compare your have : need Excess  compare your have : need

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35 Cu + AgNO 3  Cu(NO 3 ) 2 + Ag Balance first Balance first Know: you have 3.5 grams of Cu and 6 grams of AgNO 3. What is the LR and what is excess? Know: you have 3.5 grams of Cu and 6 grams of AgNO 3. What is the LR and what is excess?

36 Cu + AgNO 3  Cu(NO 3 ) 2 + Ag 3.5 grams of Cu / 6 grams of AgNO grams of Cu / 6 grams of AgNO 3

37 Al + O 2  Al 2 O 3 Balance Balance Known: mole of powdered Al is placed in a container with moles of oxygen. What is the limiting reactant? Known: mole of powdered Al is placed in a container with moles of oxygen. What is the limiting reactant?

38 Al + O 2  Al 2 O mole Al / moles of oxygen mole Al / moles of oxygen

39 Stoichiometry 1. Ratios and Proportions 2. Mole Ratios 3. Limiting Reagent 4. Yield 5. Gas Stoichiometry

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41 % Yield Theoretical Yield = calculated mass of product Theoretical Yield = calculated mass of product Actual Yield = mass of product found in lab Actual Yield = mass of product found in lab Percent Yield = actual yield x 100% Percent Yield = actual yield x 100% theoretical yield theoretical yield

42 Percent Yield Methanol can be produced through the reaction of CO and H 2 in the presence of a catalyst. Methanol can be produced through the reaction of CO and H 2 in the presence of a catalyst. CO(g) + 2H 2 (g)  CH 3 OH(l) CO(g) + 2H 2 (g)  CH 3 OH(l) If 75.0 g of CO reacts to produce 68.4 g CH 3 OH, what is the percent yield of CH 3 OH? If 75.0 g of CO reacts to produce 68.4 g CH 3 OH, what is the percent yield of CH 3 OH? 79.8%

43 % Yield Chlorobenzene, C 6 H 5 Cl is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. Chlorobenzene, C 6 H 5 Cl is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. C 6 H 6 (l) + Cl 2(g)  C 6 H 5 Cl (s) + HCl (g) C 6 H 6 (l) + Cl 2(g)  C 6 H 5 Cl (s) + HCl (g) When 36.8 g of C 6 H 6 react with an excess of Cl 2, the actual yield of C 6 H 5 Cl is 38.8 g. What is the percent yield of C 6 H 5 Cl? When 36.8 g of C 6 H 6 react with an excess of Cl 2, the actual yield of C 6 H 5 Cl is 38.8 g. What is the percent yield of C 6 H 5 Cl? 73.2%

44 % Yield Aluminum reacts with excess copper (II) sulfate according to the reaction below. If 1.85 g of Al react and the percent yield of Cu is 56.6%, what mass of Cu is produced? Aluminum reacts with excess copper (II) sulfate according to the reaction below. If 1.85 g of Al react and the percent yield of Cu is 56.6%, what mass of Cu is produced? Al(s) + CuSO 4 (aq)  Al 2 (SO 4 ) 3 (aq) + Cu(s) Al(s) + CuSO 4 (aq)  Al 2 (SO 4 ) 3 (aq) + Cu(s) 3.70 g

45 Stoichiometry 1. Ratios and Proportions 2. Mole Ratios 3. Limiting Reagent 4. Yield 5. Gas Stoichiometry

46 Molar Volume Molar volume = the space that one mole of ANY gas fills Molar volume = the space that one mole of ANY gas fills 1 mole = *22.4 liters Remember: 1 L = 1000 mL *This volume assumes standard temperature and pressure conditions

47 Molar Volume 1) A quantity of gas has a volume of cm 3. How many moles of gas are there?

48 Molar Volume 2) Hydrogen sulfide occupies 278.2cm 3. 2) Hydrogen sulfide occupies 278.2cm 3. What is the mass of the hydrogen sulfide? What is the mass of the hydrogen sulfide?

49 Gas Stoichiometry Instead of counting moles in a reaction, we can also count liters of a gas. Instead of counting moles in a reaction, we can also count liters of a gas. 1 liter of N 2 reacts with 3 liters of H 2 to produce 2 liters of NH 3

50 Gas Stoichiometry What volume of water vapor will be formed when 8.2 L of H 2 reacts with excess O 2 ? What volume of water vapor will be formed when 8.2 L of H 2 reacts with excess O 2 ? 2H 2 (g) + O 2 (g)  2H 2 O(g) Use a liter-liter ratio!

51 Gas Stoichiometry What volume of ammonia will form when 52.5 g of nitrogen reacts with excess hydrogen? What volume of ammonia will form when 52.5 g of nitrogen reacts with excess hydrogen? gN 2  mol N 2  mol NH 3  L NH 3 gN 2  mol N 2  mol NH 3  L NH 3 gN 2  mol N 2  L N 2  L NH 3 gN 2  mol N 2  L N 2  L NH 3

52 Keep digging! No pun intended


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