Slide 1Chemical EquationsSlide 3Slide 4Chemical EquationSlide 6Mole ratios: relating moles within chemical equationsSolving Mass  Moles Reaction ProblemsStoichiometry ProblemSlide 10Slide 11Sardine & Swiss on Rye SandwichSlide 13Slide 14Slide 15Limiting Reactant (or reagent)Slide 17Slide 18Using StoichiometryPercent yieldTheoretical Yield: Which Reactant is Limiting?Slide 22Slide 23Slide 24Slide 25Permanent room change for the Tuesday Chem 121 Study Group held from 2-4. Biology 234 instead of Environmental Sciences 418Chemical Equations•identifies all reactants & products•shows molar ratios between all chemical species in the reaction (“stoichiometry”)•proper stoichiometry is represented ONLY when the chemical equation is balancedChapter 43 general classes of chemical reactions:1)1)Precipitation reactionsPrecipitation reactionsEx: geology, heavy metal analysisSolid formationSolid formation from ionic compounds2) Acid/base reactions2) Acid/base reactionsEx: many biochemical reactionsProtonProton transfertransfer in polar covalent compounds3) Oxidation/Reduction (“redox”) reactions3) Oxidation/Reduction (“redox”) reactionsEx: batteries, metabolic energy production ElectronElectron transfertransfer in ionic & molecular compoundsClassifying Chemical ReactionsSimilarities in written equations1) Combination reactions (CR)•often redox2) Decomposition reactions (DR)•often redox3) Single replacement (SR)•often redox4) Double displacement (DD)•Acid/base, precipitation, redoxLabFundamental rxn. similarities1) Precipitation2) Acid/base3) RedoxTextbookChemical EquationC2H5OH + 3O2  2CO2 + 3H2OCheck that the equation is balanced.Check that the equation is balanced.•1 mole of ethanol reacts with► 3 moles of oxygen•1 mole of ethanol reacts to produce► 2 moles of carbon dioxide► 3 moles of water__ NH3 + __ O2 → __ NO + __ H2O1. Balance the chemical equation2. For every 1 mole of NH3 reacted, how many moles of NO are produced?3. How many moles of O2 react with 2.0 moles of NH3Mole ratios:relating moles within chemical equationsC3H8 + O2 CO2 + H2O1 5 3 4• If we had 2 moles of C3H8- how many moles of CO2 would be produced?- how many moles of H2O would be produced?• If we had 0.5 moles of C3H8- how many moles of O2 would be needed?Solving Mass  Moles Reaction Problemsmoles massmolar massmassA (g) Generic Reaction: aA + bB → cC + dDmolesA molesD massD (g) Mm = gramsmoleda mole ratioStoichiometry ProblemC3H8 + O2 CO2 + H2O1 5 3 4If you burned 4.4 grams of propane in a plentiful supply of oxygen- how many grams of O2 would be consumed?- how many grams of carbon dioxide would be produced?Ethanol combusts to form CO2 & water.__ C2H5OH + __ O2  __ CO2 + __ H2O 1. Balance the chemical equation2. Identify as many mole ratios as you can3. How many moles of oxygen (O2) react with 15.0 moles of ethanol4. How many grams of O2 react with 15.0 moles of ethanol5. How many g of CO2 are formed when 1.00 kg of ethanol is burned with 1.00 kg of O2Sardine & Swiss on Rye Sandwich20sardines12slices20slicesAn Ice Cream Sundae Analogy for Limiting ReactionsFig. 3.10Ethanol combusts to form CO2 & water.__ C2H5OH + __ O2  __ CO2 + __ H2O 1. Balance the chemical equation2. Identify as many mole ratios as you can3. How many moles of oxygen (O2) react with 15.0 moles of ethanol4. How many grams of O2 react with 15.0 moles of ethanol5. How many g of CO2 are formed when 1.00 kg of ethanol is burned with 1.00 kg of O2Limiting Reactant (or reagent)The limiting reactant is the reactant in a chemical reaction which limits the amount of products that can be formed.The limiting reactant in a chemical reaction is present in insufficient quantity to consume the other reactant(s).This situation arises when reactants are mixed in non-stoichiometric ratios.76.15 g/mol 32.00 g/molLimiting Reactant Example 1Add: 14 mol 20 molLimiting Reactant Example 34NH3 + 5O2 → 4NO + 6H2OCould make14 mol NOCould make16 mol NONH3 is the limiting reagent.(Use this as basis for all further calculations)Using StoichiometryStoichiometry is used to answer two fundamental questions in chemical analysis:•What is the theoretical yield?•What is the limiting reactant?REMEMBER: stoichiometry shows molar ratios not mass ratiosPercent yield actual yield % yield =actual yield: observed yield of producttheoretical yield: calculated assuming 100% conversion of the LIMITING REAGENTBoth yields can be in moles or grams theoretical yield x 100Theoretical Yield: Which Reactant is Limiting?1) calculate moles (or mass) of product formed by complete reaction of each reactant.2) the reactant that yields the least product is the limiting reactant (or limiting reagent).3) the theoretical yield for a reaction is the maximum amount of product that could be generated by complete consumption of the limiting reagent.When 66.6 g of O2 gas is mixed with 27.8 g of NH3 gas and 25.1 g of CH4 gas, 36.4 g of HCN gas is produced by the following reaction: 16.04 17.03 32.00 27.03 g/mol2CH4 + 2NH3 + 3O2 → 2HCN + 6H2O1. What is the % yield of HCN in this reaction? 2. How many grams of NH3 remain?Limiting Reactant Example 2Mass to moles66.6 g of O2 → 2.08 mol O227.8 g of NH3 → 1.63 mol NH325.1 g of CH4 → 1.56 mol CH4Which reactant is limiting? 2.08 mol O2 can yield 1.39 mol HCN (or 37.5 g) 1.63 mol NH3 can yield 1.63 mol HCN (or 44.1 g) 1.56 mol CH4 can yield 1.56 mol HCN (or 42.2 g)Conclusion?O2 is the limiting reagent.moles could also be used% yield = actual yield theoretical yieldx 100% yield = 36.4 g HCN 37.5 g HCNx 100 = 97.1%O2 is the limiting reagent. Thus, theoretical yield is based on 100% consumption of O2.2.08 mol O2 can yield 1.39 mol (or 37.5 g) HCN2. How many grams of NH3 remain?36.4 g (or 1.35 mol) of HCN gas is produced2CH4 + 2NH3 + 3O2 → 2HCN + 6H2OSince the reaction stoichiometry is 1:1, 1.35 mol of NH3 is consumed: 1.63 mol NH3 initially present – 1.35 mol NH3 consumed 0.28 mol NH3 remaining0.28 mol NH3 x (17.03 g NH3/mol) = 4.8 g NH3