Chemistry Reactions Reading Supplemental Textbook Materials Chapter 9 Pages 173 190 196 201 Avogadro s hypothesis Volume Relationships Gases react in small whole number quantities Avogadro s hypothesis chemicals react in consistent small whole number ratios Equal volumes of gases at the same temperature and pressure have the same number of molecules Combustion of propane C3H8 5 O2 3 CO2 4 H2O How much what volume of oxygen is needed to burn 0 556 L of propane Ratio of Oxygen molecules to propane molecules is 5 1 0 556 L C3H8 x 5 L O2 2 87 L O2 1 L C3H8 Problem 4 in class Combustion of propane C3H8 5 O2 3 CO2 4 H2O Calculate how much CO2 is produced when 2 L of propane is burned Atomic vs Molecular Weight Atomic weight is average in u atomic units Atomic mass specified by isotope Molecular mass is the mass of one mole of molecules in grams 6 0221367x1023 molecules Avogadro s 1 Molar mass of substances Mass of one mole of molecules of substance Numerically identical to molecular mass of molecules in atomic mass units Calculate Molar Mass CO2 molecular mass C 12 g mole O2 32 g mole Calculate Molar Mass O atomic weight 15 9996 O 16 atomic mass 16 u Molecular oxygen 16 O2 atomic mass 32 u Molecular O2 molar mass 32 g mole Molar Mass of C O2 CO2 1 mole C 12 g 1 mole O2 32 g 1 mole CO2 44 g C O2 CO2 CO2 12 32 44 g mole Example Problem NO O2 NO2 What is the molar mass of each substance in this equation What is the molar mass of each substance in this equation NO O2 NO2 14 16 30 g N2 16x2 32 g O2 14 32 46 g NO2 2 Problem 5 in class Calculate the molar mass of propane C3H8 assume molar mass of C 12 g mole assume molar mass of H 1 g mole Calculate Moles from Grams Number of moles of 176 g of CO2 Molar mass of CO2 44 g mole If you multiply you get a mess 176 g 44 g 7744 g 2 mole moles 176 g x 44 g mole results in units of g2 mole UNITS Alert you that you made an error Problem 6 in class Moles calculated from Grams Find the molar mass of substance Na 23 g mole Multiply molar mass times of moles 23 g mole x 0 250 moles 5 75 g Moles calculated from Grams Instead divide 176 g by 44 g mole 176 g 44 g mole 176 g x Or look at it as 144mole g 4 moles CO2 Moles of substances How many moles of Si 28 are there in 140 g of Si 28 Be SURE to include UNITS 3 Standard temperature and pressure Mass to moles relationship 0o C Sea level pressure 29 92 Hg 1 mole of gas 22 4 Liters about 0 8 ft3 Has mass of its formula mass Mass of materials in chemical equations Determine molar ratios from balanced equation Calculate molar mass of reactants and products Convert mass of quantity given to moles Convert moles of unknown from molar mass ratios Convert back to grams from this molar amount Problem C O2 CO2 Molar ratio 1 1 1 4 grams oxygen 1 mole O2 32 g 4 g O2 1 mole 0 125 moles O2 32 g Problem C O2 CO2 Molar ratio 1 1 1 4 grams oxygen Grams carbon consumed Grams carbon dioxide produced Problem C O2 CO2 Molar ratio 1 1 1 0 125 moles O2 in 1 1 ratio 0 125 moles C 0 125 moles CO2 4 C O2 CO2 Example Problem 0 125 moles C Grams carbon consumed 0 125moles C 12 g 1 5 g C 1 mole 0 125 mole CO2 44 g 5 5 g CO2 1 mole 2 NO O2 2 NO2 Problem Find moles of quantity given 30 g NO I mole Find moles of unknown Molar ratios 2 2 reduces to 1 1 1 mole NO2 How many grams 1 mole NO2 Problem NO O2 NO2 30 grams NO How many grams NO2 produced Balance Equation Determine molar ratios 2 1 2 Find molar mass of each component N 14 g O 16 g NO 30 g NO2 46 g Problem H 2 S O2 SO2 H 2O 32 grams SO2 How many grams O2 used 46 g 46 g NO2 1 mole Problem H 2 S O2 SO2 H 2O Balance first 2 H 2 S 3O2 2SO2 2 H 2O Then determine molar ratios 2 SO2 to 3 O2 Problem 2 H 2 S 3O2 2SO2 2 H 2O Find molar masses 2x1 H 2 32 S 2x16 O 32 S 32 O2 2x1 H 16 O 34 g mol H2S 32 g mol O2 64 g mol SO2 18 g mol H2O 5 Problem Problem 2 H 2 S 3O2 2 SO2 2 H 2O 2 H 2 S 3O2 2 SO2 2 H 2O 32 g SO2 needs how many grams O2 How many moles is 32 g SO2 32 g SO 2 1 mole 0 5 moles SO 2 64 g 32 g SO2 needs how many grams O2 How many moles O2 is needed 0 5 moles SO2 in 2 3 ratio with O2 32 g SO 2 Proportions Proportions Mathematical device to compare ratios Be sure you keep same same in columns and rows molar amount g Example molar amount or 1 mole 0 5 moles SO 2 64 g correctly organized cross multiply to solve g molar amount molar amount g g Solution to NO2 3 moles O2 x moles O2 2 moles SO2 0 5 moles SO2 correctly organized cross multiply to solve 0 75 moles of O2 react with 0 5 moles SO2 Solution 0 75 moles of O2 is how many grams 0 75 moles O2 32 g 24 g O2 1 mole 6
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