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WOU ES 105 - Chemical Reactions

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Chemical ReactionsChemical EquationsBalancing Chemical EquationsWater balancingBalancing TipsRusting of IronProblem 1 in classCombustion of propaneProblem 2 in classVolume RelationshipsAvogadro’s hypothesisCombustion of propaneProblem 3 in classAtomic vs. Molecular WeightCalculate Molecular MassProblem 4 in classGrams calculated from MolesMoles calculated from GramsMoles calculated from GramsProblem 5 in classMass to moles relationshipTo convert between grams and molesProportionsProportions to find grams and molesProportionsProblemProblemProblemProblemProblemProblemProblemProblemProblemSet up proportionProblem 6Reaction SpeedChlorine catalystEnergy of reactionsChemical ReactionsChapter 17Chemical Equations•C+O2 ÆCO2•C(s) +O2 (g) ÆCO2 (g)• Reactants on left, products on right• Each are balanced because same number of atoms of reactants as products• Some equations show the phase of the substances also: solid, liquid, gasBalancing Chemical Equations• Molecules of reactants and products shown—– Cannot change the molecule– Can change how many of them• Cannot add or delete reactants or products• Balanced—equal number of same atoms on each sideWater balancingBalancing Tips• Never change the molecular formula of reactants or products• Count atoms in reactant and products• Always add whole molecules, not parts• Start by balancing atoms in compounds• Save element reactants or products for last—to make up any imbalanceRusting of Iron•Fe + O2Æ Fe2O3not balanced• start with oxygen• Fe + 3 O2Æ2 Fe2O3• next do iron•4 Fe + 3 O2Æ2 Fe2O3Problem 1 in classBalance the following equation, on the worksheet provided. (Put your name on the back of the sheet, please.)N2 + H2Æ NH3Combustion of propane•C3H8+ O2Æ CO2+ H2O• fix hydrogen first—it’s in two compounds•C3H8+ O2Æ CO2+ 4 H2O• need more carbon product•C3H8+ O2Æ 3 CO2+ 4 H2O• Do oxygen last, because it is single•C3H8+ 5 O2Æ 3 CO2+ 4 H2OProblem 2 in classBalance the following chemical equation, the combustion of methaneCH4+ O2Æ CO2+ H2OMethane oxygen carbon dioxide waterVolume Relationships• Equal volumes of gases at the same temperature and pressure have the same number of molecules• Gases react in small whole number quantities• Avogadro’s hypothesis: chemicals react in consistent, small whole number ratiosAvogadro’s hypothesisCombustion of propaneC3H8+ 5 O2Æ 3 CO2+ 4 H2O• What volume of oxygen is needed to burn 0.5 L of propane?• Ratio of Oxygen molecules to propane molecules is 5:1• 0.5 L x 5 L O2= 2.5 L Oxygen1 L PropaneProblem 3 in class• Combustion of propaneC3H8+ 5 O2Æ 3 CO2+ 4 H2OCalculate how much CO2 is produced when 2 L of propane is burnedAtomic vs. Molecular Weight• Atomic weight on periodic table is average of natural abundance of isotopes• Atomic mass is the number of nucleons in a particular atom—specified by isotope• Molecular mass is the mass of one mole of molecules– One atomic mass number of grams– 6.0221367x1023moleculesCalculate Molecular Mass• O atomic weight 15.9996 (round to 16 for this class)• O-16 atomic mass 16 u• Molecular oxygen O2 atomic mass 32 u• Molecular O2molecular mass 32 g/mole•CO2molecular mass C=12 g/mole, O2=32 g/mole CO2=12+32=44 g/moleProblem 4 in class• Calculate the molar mass of propane C3H8• Round atomic weight of C to 12• Round atomic weight of H to 1molegmolegGrams calculated from Moles• Can find the molar mass of substance Na=23 mole of Na • Multiply molar mass times moles• 23 x 0.250 moles = 5.75 gmoleg41molegMoles calculated from Grams• 176 g of CO2 = Number of moles?• Molar mass of CO2 = 44 • If you multiply,  176 g x 44 results in units of you get a unit mess UNITS alert you that you made an error KEEP UNITS WITH NUMBERS!!molegmoleg2molegMoles calculated from Grams• 176 g of CO2 = Number of moles?• Molar mass of CO2 = 44 • Divide 176 g by 44• Same as multiply by reciprocal• Now the grams cancel =)moleg176 g x (1 mole44 g)= 4 moles CO2molegProblem 5 in class132 g of propane is how many moles?Mass to moles relationshipTo convert between grams and moles• Make sure equation is balanced• So you know the molar ratios of them• Find molar mass of them• Set up proportions for moles and gramsProportions• Mathematical device to compare ratios• Cross-multiply to solve• Correctly organized• Be sure you keep same:same in columns and rowsProportions to find grams and moles• Correctly organizedExampleor• cross-multiply to solveb of a of b of molesa of molesgg=b of b of molesa of a of molesgg=Proportions• Correctly organized• It doesn’t matter how you write the first ratio, as long as you label the numbers• Try to put unknown on the top—easier to solve• The second ratio needs to match the firstProblem• 64 grams O2• How many grams NO2produced?22NOONO →+First: Balance Equation2222 NOONO →+Problem• 64 grams O2• How many grams NO2produced?Balance EquationDetermine molar ratios of them 1:2Find molar mass of each component NO2=46 g, O2=32 g, (NO=30 g)2222 NOONO →+Problem• 64 grams O2• How many grams NO2produced?Molar mass of each: O2=32 g, NO2=46 g How many moles is 64 grams O2?One mole2222 NOONO →+Problem• 64 grams O2• How many grams NO2produced?• Molar mass of eachO2=32 g, NO2=46 gMolar ratios O2:NO2 is 1:2Two mole of O2So four moles of NO2 is producedHow many grams is that?4 mol x 46 g/mol = 184 grams2222 NOONO →+ProblemOHSOOSH2222+→+• 32 grams SO2• How many grams O2used?Problem• Balance first• Then determine molar ratios•2 SO2 to 3 O2OHSOOSH2222+→+OHSOOSH22222232+→+• 32 grams SO2• How many grams O2used?Problem• Find molar masses SO2= 32 + 32 = 64 g/mol SO2 O2 = (2x1) +16 = 32 g/mol O2 H2O= (2x1) +16 = 18 g/mol H2O H2S= (2x1) +32 = 34 g/mol H2S OHSOOSH22222232+→+• 32 grams SO2• How many grams O2used?ProblemOHSOOSH22222232+→+• 32 g SO2needs how many grams O2?• How many moles is 32 g SO2?22SO 5.0g 64 1SO g 32 molesmole=⋅• 32 grams SO2• How many grams O2used?ProblemOHSOOSH22222232+→+• How many moles O2 is needed?• 0.5 moles SO2in 2:3 ratio with O2• 0.75 moles O222SO 5.0g 64 1SO g 32 molesmole=⋅• 32 grams SO2• How many grams O2used?Set up proportionwith the unknown on top (the O2)[][][] O g ?2=• 32 grams SO2• How many grams O2used?Problem 6Is it balanced?Molar ratio 1:1:1 4 grams oxygen


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WOU ES 105 - Chemical Reactions

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