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Stoichiometry Chapter 9
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Big picture Ch. 7 The mole Ch.8 Balancing Chemical Equations Ch.9 “Stoichiometry” Target: How many grams of carbon dioxide are produced by burning 411 g of gasoline?
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Notes Stoichiometry Theproportionalrelationshipbetweentwoormoresubstancesduringachemicalreaction. The proportional relationship between two or more substances during a chemical reaction.
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Real world stoichiometry problem
1 stick of butter + 3 eggs 2 cupcakes 1. If you have 60 eggs how many cupcakes can you make? (assuming you have unlimited butter) 2. How many eggs does it take to make 300 cupcakes? 1. ANS = 40 cupcakes 2. ANS = 450 eggs
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9.1 Practice: mole-to-mole conversion
C3H8 + 5O2 3CO2 + 4H2O You have 4 mole of propane, (C3H8) How many moles of O2 will it react with when it burns? How many moles of CO2 form when it burns? How many moles of H2O form when it burns?
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9.1 Practice: Mole-to-mole conversion
Given the following equation: N2 + 3H2 2NH3 Calculate the number of moles of hydrogen needed to prepare 312 moles of ammonia. See Graphic Organizer on p. 303
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Notes Mole Ratio Used as conversion factor in stoichiometry problems.
x moles of unknown y moles of given x = coefficient of unknown in balanced chem eqn y = coefficient of given in balanced chem eqn
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9.1 Mole to Mole conversions
Practice P. 304 # 1a,b # 2 a,b,c P. 329 #21*,22,23 *h’wk
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Mass-to-Mass conversion
See step-by-step procedure on p. 305 See graphic organizer on p. 306
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Mass-to-Mass conversion
Typical Question Imagine 7.5g of nitrogen gas (N2) reacts with excess* hydrogen gas per the following equation: N2 + 3H2 2NH3 Calculate the mass of ammonia (NH3) produced * Excess = “An amount or quantity beyond what is sufficient; a surplus.” = IGNORE!
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Mass-to-Mass conversion
Imagine 7.5g of nitrogen gas (N2) reacts with excess hydrogen gas per the following equation: N2 + 3H2 2NH3 Calculate the mass of ammonia (NH3) produced. What is the ‘Given’ in the question? What is the ‘Unknown’ in the question? What is the molar mass of given and unknown? What is the mole ratio that connects the Given and the Unknown? ANSWER = 9.1 g
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Stoichiometry calcs SUMMARY
WHEN IN DOUBT……TO BEGIN, CONVERT GIVEN TO MOLES When one of the reactants is in excess ignore it.
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9.1 Stoichiometry problems involving mass
What mass of NH3 can be made from 1221g of H2? N2 + 3H2 2NH3 See Skills Toolkit 3 p. 306
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9.1 Stoichiometry Problems Involving Mass
Sample Problem B (Follow along on P. 307) What mass of NH3 can be made from 1221 g H2? N2 + 3H2 2NH3
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9.1 Stoichiometry Problems Involving Mass
What mass of NH3 can be made from 1221g of H2? N2 + 3H2 2NH3 GIVEN: mass of H2 = 1221 g molar mass of H2 = 2.02 g/mol Mole ratio: 3 mol H2 = 2 mol NH3 UNKNOWN mass of NH3 = ? g ( will need molar mass of NH3 = g/mol)
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9.1 Stoichiometry Problems Involving Mass
Step 1: To change grams to moles, use the molar mass of H2. Step 2: The mole ratio must cancel out the units of mol H2 given in the problem and leave the units of mol NH3. Therefore, the mole ratio is: Step 3: To change moles of NH3 to grams, use the molar mass of NH3.
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9.1 Stoichiometry Problems Involving Mass
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See page 305 for procedure 9.1 Problems Involving Mass
For Mass Calculations, Use Molar Mass A mass-mass problem is a three-step process. Step 1: Convert the given mass into moles. Step 2: Use the mole ratio to convert moles of given to moles of unknown. Step 3: Convert moles of known into grams. See page 305 for procedure
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Practice Calculate the mass of hydrogen that would be needed to make 100 g of ammonia.
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Practice: Stoichiometry Scratch paper
Calculate the mass of water formed from the combustion of 83 g of ethane C2H6 Balance the equation GUESS Write the 3 conversion factors will you need ANS = 149 g
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9.1 Practice p. 311 # 4 a,b How many grams of BrCl form when 212 g of Br2 react w/ excess Cl2?
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9.1 Stoichiometry Problems Involving Mass
Practice See page 305 for procedure P. 307 #1,2,3,4* P. 330 # 24,25*,26** * Show work to teacher when done ** Beast Mode
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Next Generation Science Standard (NGSS)
HS-PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. The Mole (Ch.7) Balancing Equations (Ch.8) Stoichiometry (Ch.9)
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Combustion: CH4 + 2O2 CO2 + 2H2O
‘High Energy’ = ‘Reactive’ = ‘Unstable’ e.g. gasoline Low Energy = ‘Unreactive’ ‘Stable’ e.g. carbon dioxide
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Photosynthesis
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Global Warming
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9.1 Stoichiometry Problems Involving Mass
One gallon of gasoline (C8H18) weighs 2835 g. Calculate the mass of carbon dioxide produced by the combustion of one gallon of gasoline. Follow along w/ Skills Toolkit p. 306 ANS = 8736 g
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9.1 Stoichiometry Problems Involving Mass
Gathering Information Write the balanced chemical equation for the combustion of octane, C8H18 Calculate the molar mass of octane C8H18 Calculate the molar mass of carbon dioxide
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Mass-Mass Stoich: Cellular Respiration
Calculate the number of grams of water that would theoretically be produced in cellular respiration by the combustion of 75.2 g of glucose.
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Brainteaser A bike shop has 10 bike frames and 16 wheels. How many complete bicycles can be assembled using these parts? What would be left over? 8 complete bicycles. 2 frames left over.
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Notes Limiting Reactant
Thesubstancethatcontrolsthequantityofproductthatcanforminachemicalreaction
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Notes Limiting Reactant
The substance that controls the quantity of product that can form in a chemical reaction. It runs out first Excess Reactant Thesubstancethatisnotusedupcompletelyinachemicalreaction
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Notes Excess Reactant The substance that is not used up completely in a chemical reaction. Ignore it! P. 313
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Real world analogy: Limiting reagent
1egg + 3 spoonfuls of butter 2 cupcakes If you have 9 eggs and 9 spoonfuls of butter, how many cupcakes can you make? What ingredients would be left over? How much? What ingredient would run out first? 6 cupcakes (theoretical yield) 6 eggs left over (eggs are in excess) Butter is the ‘limiting reactant’.
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9.2 Limiting Reagent and Theoretical Yield
Practice: p. 331 # 33 p. 317 # 1,3,2
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