Chemical R Reactions ti Chapter 17 click here for 9 page to print Atomic vs vs Molecular Weight Atomic weight on periodic table is average of natural abundance of isotopes p Atomic mass is the number of nucleons in a particular atom atom specified 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 round to 16 for this class O 16 atomic mass 16 u Molecular M l l oxygen O2 atomic t i mass 32 u Molecular o ecu a O2 molecular o ecu a mass ass 3 32 g g mole oe CO2 molecular mass C 12 g mole O2 32 g mole CO2 12 32 44 12 32 44 g mole Na2CO3 molecular mass Na 23 g mole C 12 g mole O 16 g mole 3 O so multiply 16 x 3 23 12 48 83 g mole Write these down C 12 H 1 O 16 Use for the next question What is the sum of the atomic masses of all the atoms in sucrose C12H22O11 1 2 2 3 4 182 amu 270 amu 342 amu none of the above 0 1 0 0 2 3 0 4 Grams calculated from Moles Find the molar mass of substance g Na 23 mole 1 4 mole of Na Multiply molar mass times moles g 23 mole x 0 250 moles 5 75 g Moles calculated from Grams 176 g of CO2 Number of moles g Molar mass of CO2 44 mole If you multiply g mole l 176 g x 44 results in units of you get a unit mess g2 mole UNITS alert you that you made an error KEEP UNITS WITH NUMBERS Moles calculated from Grams 176 g of CO2 Number of moles g Molar mass of CO2 44 mole g Divide 176 g by 44 mole Same as multiply by reciprocal 176 g x 1 mole 44 g Now the grams cancel 4 moles CO2 Mass to moles relationship To 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 grams Proportions Mathematical device to compare ratios Cross multiply to solve Correctly organized Be sure you keep same same in columns and rows Proportions to find grams and moles Correctly organized Example moles of a g of a moles of b g of b or moles of a moles of b g off a g off b cross multiply cross multiply to solve Proportions Correctly organized It doesn doesn tt matter how you write the first ratio ratio as long as you label the numbers Try T to t putt unknown k on the th top easier t i tto solve The second ratio needs to match the first Problem NO O2 NO2 64 grams O2 How manyy g grams NO2 p produced First Balance Equation 2 NO O2 2 NO2 Problem 2 NO O2 2 NO2 64 grams O2 How manyy g grams NO2 p produced Balance Equation Determine molar ratios of them 1 2 Find molar mass of each component NO2 46 46 g O2 32 32 g NO NO 30 30 g Problem 2 NO O2 2 NO2 64 grams O2 How manyy g grams NO2 p produced Molar mass of each O2 32 g NO2 46 g How many moles is 64 grams O2 One mole Problem 2 NO O2 2 NO2 64 grams O2 How manyy g grams NO2 p produced Molar mass of each O2 32 g NO2 46 g Molar ratios O2 NO2 is 1 2 Two mole of O2 So four moles of NO2 is produced How many grams is that 4 mol x 46 g mol 184 grams Problem H 2 S O2 SO2 H 2O 32 grams SO2 How many grams O2 used Problem 32 grams SO2 How many grams O2 used 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 32 grams SO2 How many grams O2 used 2 H 2 S 3O2 2SO2 2 H 2O Find molar masses SO2 32 32 O2 2x1 16 H2O 2x1 16 H2S 2x1 32 64 g mol SO2 32 g mol O2 18 g mol H2O 34 g g mol H2S Problem ob e 32 grams SO2 How many grams O2 used 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 32 grams SO2 How many grams O2 used 2 H 2 S 3O2 2SO2 2 H 2O How many moles O2 is needed 0 5 moles SO2 in 2 3 ratio with O2 0 75 moles O2 1 mole 32 g SO 2 0 5 moles SO 2 64 g 32 grams SO2 How many grams O2 used Set up proportion with ith th the unknown k on ttop th the O2 g O2 Problem 6 C O2 CO2 Is it balanced 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 32g 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 0 125 l 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 Formation of water
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