1. Honors Chem Unit 12 Stoich Notes
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

2. 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!!

3. Notes
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?

4. 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

5. 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)

6. 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
Write up Stoich lab pg 251

7. 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

8. 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?

9. 2Cu (s) + S (s)  Cu2S(s)
What is the limiting reactant when g Cu reacts with 25.0 g S?
How many g Cu2S can be formed?
How much of the excess reactant is left?

10. % 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)

11. Actual yield- amt. of product formed in lab
Theoretical yield- amt. product that could be formed from calculations
% Yield: actual yield X 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?