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

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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.

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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:

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

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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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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.

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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

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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

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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 )

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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

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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

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Heart of Every Equation mol unknown = mol given mol given

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

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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

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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?

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

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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?

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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

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

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

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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

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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

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

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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

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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?

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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?

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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

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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

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

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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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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?

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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

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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?

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

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

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% 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

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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%

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% 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%

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% 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

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

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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

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

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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?

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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

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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!

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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

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Keep digging! No pun intended

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