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 Chapter 17 One atomic mass number of grams 6.0221367x1023 molecules CO molecular mass Calculate Molecular Mass 2 O atomic weight 15.9996 (round to 16 . C=12 g/mole, O2=32 g/mole for this class) . CO2=12+32=44 g/mole O-16 atomic mass 16 u Molecular oxygen O2 atomic mass 32 u Molecular O2 molecular mass 32 g/mole Na2CO3 molecular mass Write these down Na = 23 g/mole C = 12 C = 12 g/mole H = 1 O = 16 g/mole O = 16 2N2 Na, 3O3 O, so mu ltilltiply N14N = 14 2(23) + 12 + 3(16) = 106 g/mole K = 39 Cl = 35.5 Use for some questions 1 How many grams of oxygen can be How many grams of oxygen can be produced from 122.45 g of KClO3? produced from 122.45 g of KClO3? 2 KClO3 2 KCl + 3 O2 2 KClO3 2 KCl + 3 O2 1. First find molecular masses of substances 1. 32.00 g 2. Convert 122.45 g of KClO3 to moles 2. 48.00 g 3. Find molar ratios from balanced equation 3. 61. 22 g 4. Calculate moles of O2 4. 122.45 g 5. Convert that to grams of O2 0% 0% 0% 0% 1234 How many grams of water are produced from 1.25 moles of methane? Moles calculated from Grams 1 CH4 + 2 O2 2 H2O+ 1 CO2 176 g of CO2 = Number of moles? 1. 11.25 grams g Molar mass of CO2 = 44 mole 2. 22.5 grams If you multiply, g g2 . 176 g x 44 results in units of 3. 45 grams mole mole 4. 90 grams . you get a unit mess . UNITS alert you that you made an error . KEEP UNITS WITH NUMBERS!! 0% 0% 0% 0% 1234 Mass to moles relationship To convert between grams and moles Find molar mass Divide grams by molar mass 2 Proportions Proportions Mathematical device to compare ratios Correctly organized Cross-multiply to solve Label the numbers Correctly organized Be sure you keep molar ratio on one side of the Try to put unknown on the top—easier to solve equal sign The secon d ra tio nee ds to hbtihave substances in Put the ratio of unknown to known on the other same position as the first side Be sure same substance is on top on both sides…so the other substance is on bottom on both sides… Problem Problem 2NO O2 2NO2 NO O2 NO2 64 grams O2 64 grams O2 How many grams NO2 produced? How many grams NO2 produced? First: Balance Equation Balance Equation Determine molar ratios of them 1:2 Find molar mass of each component NO =46 g, O =32 g, (NO=30 g) 2NO O2 2NO2 2 2 Problem 2NO O2 2NO2 Problem 2NO O2 2NO2 64 grams O2 64 grams O2 How many grams NO2 produced? How many grams NO2 produced? Molar mass of each O2=32 g, NO2=46 g Molar mass of each: O2=32 g, NO2=46 g Molar ratios O2:NO2 is 1:2 How many moles is 64 grams O2? Two mole of O2 One mole So four moles of NO2 is produced How many grams is that? 4 mol x 46 g/mol = 184 grams 3 • 32 grams SO2 Problem Problem • How many grams O2 used? H S O SO H O 2 2 2 2 H2S O2 SO2 H2O Balance first • 32 grams SO2 • How many grams O used? 2 2H2S 3O2 2SO2 2H2O Then determine molar ratios 2 SO2 to 3 O2 • 32 grams SO • 32 grams SO 2 Problem 2 Problem • How many grams O2 used? • How many grams O2 used? 2H 2S 3O2 2SO2 2H 2O 2H2S 3O2 2SO2 2H2O • 32 g SO2 needs how many grams O2? Find molar masses • How many moles is 32 g SO2? . SO = 32 + 32 = 64 g/mol SO 2 2 1 mole . O = (2x1) +16 = 32 g/mol O 32 g SO2 0.5 moles SO2 2 2 64 g . H2O= (2x1) +16 = 18 g/mol H2O . H2S = (2x1) +32 = 34 g/mol H2S • 32 grams SO2 • 32 grams SO2 Set up Problem • How many grams O2 used? • How many grams O2 used? proportion 2H 2S 3O2 2SO2 2H 2O • How many moles O is needed? 2 with the unknown on top (the O2) •0.5 moles SO2 in 2:3 ratio with O2 • 0.75 moles O ? g O 2 2 1 mole 32 g SO 0.5 moles SO 2 64 g 2 4 Problem 6 C O2 CO2 Problem 6 C O2 CO2 Is it balanced? Molar ratio 1:1:1 Molar ratio 1:1:1 4 grams oxygen 4 grams oxygen 1 mole O2 = 32 g . Grams carbon consumed? . Grams carbon dioxide produced? 1mole 4g O 0.125 moles O 2 32g 2 Problem 6 C O2 CO2 Problem 6 C O2 CO2 Molar ratio 1:1:1 0.125 moles C Grams carbon consumed? 0.125 moles O in 1:1 ratio 2 12g 0.125moles C 1.5g C 0.125 moles C 1 mole 0.125 moles CO2 44g 0.125 mole CO 5.5g CO 2 1 mole 2 Reaction Speed Chlorine catalyst Collision of molecules required for it to occur Increase concentration Increase temperature Catalyst can facilitate reaction 5.