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?