Chem Ch 9 Notes• 9.1 Stoichiometry- calculation of quantities in chemical reactions• From the coefficients in a BALANCED equation you can get: • N2+3H2 2NH3• 1. # particles (molecules, formula units, atoms) • 1 molecule N2: 3 molecules H2 : 2 molecules NH3• 2. # moles • 1 mole N2: 3 mole H2 : 2 mole NH3
• 3. Mass- Obeys Law of Conservation of Mass • 1 mol N2 = 28.0 g • +3 mol H2 = 6.0 g • 2 mol NH3 = 34.0 g• 4. Volume- GASES at STP 1 mol= 22.4L• 3 mol H2 = 3(22.4)=67.2L• 1 mol N2 = 1(22.4) = 22.4 L• 2 mol NH3 = 2(22.4) = 44.8 L• Notice that the number of atoms & mass are always conserved, but the volume & molecules may not be!!
• Mole-Mole calculations • N2+3H2 2NH3 • 1mol N2 1moleN2 2 mol NH3 3 mol H2 2mol NH3 3 mol H2 These are your mole conversion factors How many moles of NH3 are in 0.60 mol N2?
• Mass:Mass• 1. Convert mass to moles (1mol/ g)• 2. Convert moles of what you have to moles of what you want• 3. Convert mol to mass ( g/1mol)• How many g NH3 are produced when 5.40 g of H2 react w/ excess N2?• For all problems• Convert to mol, use mol:mol, convert to wanted units
• How many moles O2 are produced when 29.2 g H2O decomposed into O2 & H2?• Assuming STP, how many L O2 are needed to produce 19.8 L SO3? • 2SO2(g) + O2(g) 2 SO3(g)
• Use ratios from coefficients b/c the volumes relate from 22.4L=1mol • 2NO(g) + O2 (g) 2 NO2(g) • How many mL NO2 are produced when 3.4mL O2 react with excess NO at STP? • 1mL O2=2 mL NO2=2 mL NO
• Limiting reactant & % Yield• Limiting Reagent- determines amt. Of product formed, runs out 1st• Steps: (if given 2 reactants) • 1. Solve for same product • 2. One w/least amount of product is limiting • 3. Other is excess (left over) • 4. Limiting determines the amount of product
• 2 Na(s) + Cl2 (g) 2NaCl (s)• Suppose 8.70 mol Na react w/3.20 mol Cl2. • What is limiting reactant? • How many moles of NaCl are produced? • How many g NaCl are produced? • How much of the excess reactant is left?
• 2Cu (s) + S (s) Cu2S(s) • What is the limiting reactant when 80.0 g Cu reacts with 25.0 g S? • How many g Cu2S can be formed? • How much of the excess reactant is left?
• % yield- measures the efficiency of reaction • Normally can’t be larger than 100% • Most are less than 100 % b/c: • Reactions don’t go to completion • Impure reactants • Competing side reaction • Loss of product during transfer or filtration • Human error (bad measurement, miscalculation)
• Actual yield- amt. of product formed in lab• Theoretical yield- amt. product that could be formed from calculations• % Yield: actual yield X 100 theoretical yield• CaCO3 (s) CaO (s) + CO2 (g) • What is the theoretical yield of CaO if 24.8 g CaCO3 is heated? • What is the % yield if 13.1 g CaO is produced?