Chemistry Chapter 17 Chemical Equations C O2 CO2 C s O2 g CO2 g Reactants on left products on right Each are balanced because same number of atoms of reactants as products Balancing 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 side Water balancing Rusting of Iron Fe O2 Fe2O3 not balanced start with oxygen Fe 3 O2 2 Fe2O3 next do iron 4 Fe 3 O2 2 Fe2O3 Problem 1 in class Balance the following equation on the worksheet provided Put your name on the back of the sheet please N2 H2 NH3 Problem 1 N2 H2 NH3 N2 H2 NH3 fix hydrogen N2 3 H2 2 NH3 When H is fixed N is already done Combustion of propane C3H8 O2 CO2 H2O fix hydrogen C3H8 O2 CO2 4 H2O need more carbon product C3H8 O2 3 CO2 4 H2O Do oxygen last because it is single C3H8 5 O2 3 CO2 4 H2O Problem 2 in class Balance the following chemical equation the combustion of methane CH4 O2 CO2 H2O Problem 2 CH4 O2 CO2 H2O CH4 O2 CO2 H2O fix hydrogen CH4 O2 CO2 2 H2O Work on oxygen CH4 2O2 CO2 2H2O Now check to see if you are done Volume 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 ratios Avogadro s hypothesis Combustion of propane C3H8 5 O2 3 CO2 4 H2O How much what volume of oxygen is needed to burn 0 5 L of propane Ratio of Oxygen molecules to propane molecules is 5 1 2 5 L Oxygen 0 5 L x 5 L O2 1 L Propane Problem 3 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 3 Combustion of propane C3H8 5 O2 3 CO2 4 H2O Ratio of Propane to CO2 1 3 2 L Propane x 3 L CO2 1 L Propane 6 L CO2 Atomic 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 0221367x1023 molecules Calculate Molecular Mass O atomic weight 15 9996 O 16 atomic mass 16 u Molecular oxygen O2 atomic mass 32 u Molecular O2 molecular mass 32 g mole CO2 molecular mass C 12 g mole O2 32 g mole CO2 12 32 44 g mole Problem 4 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 4 Molar mass of propane C3H8 assume molar mass of C 12 g mole 3 C x 12 g mole 36 g mole assume molar mass of H 1 g mole 8 H x 1 g mole 8 g mole 8 36 44 g mole C3H8 Grams calculated from Moles Can find the molar mass of substance Na 23 g mole Multiply molar mass times moles 23 g mole x 0 250 moles 5 75 g Moles calculated from Grams 176 g of CO2 Number of moles Molar mass of CO2 44 g mole If you multiply you get a mess 176 g x 44 g mole results in units of g2 mole UNITS Alert you that you made an error Moles calculated from Grams 176 g of CO2 Number of moles Molar mass of CO2 44 g mole Instead divide 176 g by 44 g mole Same as multiply by reciprocal 176 g x 1 mole 44 g 4 moles CO2 Problem 5 in class 132 g of propane C3H8 is how many moles 44 g mole propaneC3H8 1mole 3moles 132 g 44 g Mass to moles relationship Proportions Mathematical device to compare ratios Be sure you keep same same in columns and rows moles of a g of a Example moles of b or g of b moles of a moles of b g of a g of b Proportions correctly organized cross multiply to solve Problem NO O2 NO2 30 grams NO How many grams NO2 produced Balance Equation 2 NO O2 2 NO2 Problem 2 NO O2 2 NO2 30 grams NO How many grams NO2 produced Balance Equation Determine molar ratios 2 1 2 Find molar mass of each component NO 30 g NO2 46 g N 14 g O 16 g Problem 2 NO O2 2 NO2 30 grams NO How many grams NO2 produced Find molar mass of each component NO 30 g NO2 46 g N 14 g O 16 g How many moles is 30 grams NO One mole Problem 2 NO O2 2 NO2 30 grams NO How many grams NO2 produced Molar mass of each component N 14 g O 16 g NO 30 g NO2 46 g One mole of NO Molar ratios 2 1 2 So one mole of NO2 is produced How many grams is that Problem H 2 S O2 SO2 H 2O 32 grams SO2 How many grams O2 used 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 S 32 O2 32 H 2x1 O 16 H 2x1 2 S 32 O 2x16 64 g mol SO2 18 g mol H2O 34 g mol H2S 32 g mol O2 Problem 2 H 2 S 3O2 2SO2 2 H 2O 32 g SO2 needs how many grams O2 How many moles is 32 g SO2 1 mole 32 g SO 2 0 5 moles SO 2 64 g Problem 2 H 2 S 3O2 2SO2 2 H 2O 32 g SO2 needs how many grams O2 How many moles O2 is needed 0 5 moles SO2 in 2 3 ratio with O2 1 mole 32 g SO 2 0 5 moles SO 2 64 g Problem 6 C O2 CO2 Molar ratio 1 1 1 4 grams oxygen Grams carbon consumed Grams carbon dioxide produced Problem 6 C O2 CO2 Molar ratio 1 1 1 4 grams oxygen 1 mole O2 32 g 1 mole 4 g O2 0 125 moles O2 32 g Problem 6 C O2 CO2 Molar ratio 1 1 1 0 125 moles O2 in 1 1 ratio 0 125 moles C 0 125 moles CO2 Problem 6 C O2 CO2 0 125 moles C Grams carbon consumed 12 g 0 125moles C 1 5 g C 1 mole 44 g 0 125 mole CO2 5 5 g CO2 1 mole Reaction Speed Collision of molecules required for it to occur Increase concentration Increase temperature Catalyst can facilitate reaction Chlorine catalyst Energy of reactions Release energy EXOTHERMIC Methane combustion Consume energy ENDOTHERMIC …
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