1. Limiting & Excess

2. Cookie Stoichiometry To make one batch, it requires:
2 eggs
2 cups of flour
2/3 cups of butter
How many batches could you make with…
4 eggs
6 cups of flour
2/3 cups of butter
The cups of butter was your limiting reagent
The eggs and flour were your excess reagents
But how could you show this mathematically…?

3. 2 Together…. 3 on your Own!
Whiteboard!

4. Example 1
20.00 g of H2 react with g of O2 according to the reaction 2 H2 + O2  2 H2O Which reactant is limiting and which reactant is in excess?

5. Example 1 1. Calculate the number of moles of a product formed.
Mole of H2O (based on H2) =
20.00 g H2 x
1 mol H2
2 mol H2O
10.0 mole H2O
2.0 g H2
2 mol H2
Mole of H2O (based on O2) =
100.0 g O2 x
1 mol O2
2 mol H2O
6.25 mol H2O
32.0 g O2

6. Example 1
Determine the limiting and excess reactants. O2 is the limiting reactant. H2 is the excess reactant. 2. How much H2 (in grams) is left after O2 runs out?

7. Example 1
3. To find mass of H2 in excess, find the mass of H2 which will react based on the mass of the limiting reactant.
Mass of H2 (based on O2) =
100.0 g O2 x
1 mol O2
2 mol H2
2.0 g H2
12.5 g H2
32.0 g O2
1 mol H2

8. Example 1
4. Then, subtract the mass of H2 which reacts from the starting mass of H2. Mass of H2 (in excess) = mass H2 (at start) – mass H2 (reacted) = g – 12.5g = 7.5 g
Take Attendance

9. FeCl2 + KNO3 + HCl  FeCl3 + NO + H2O + KCl
Example 2
If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction
FeCl2 + KNO3 + HCl  FeCl3 + NO + H2O + KCl
What is the limiting reactant?
How many grams of each “excess” reactant left in the reaction vessel?

10. 3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl
Example 2
If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction
3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl
What is the limiting reactant?
How many grams of each “excess” reactant left in the reaction vessel?

11. 3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl
Example 2
If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction
3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl
What is the limiting reactant? KNO3
How many grams of each “excess” reactant left in the reaction vessel?

12. 3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl
Example 2
If 56.8 g of FeCl2, 14.9 g of KNO3 and 40.0 g of HCl are mixed according to the reaction
3 FeCl2 + KNO3 + 4 HCl  3 FeCl3 + NO + 2 H2O + KCl
What is the limiting reactant? KNO3
b) How many grams of each “excess” reactant are actually present in excess? FeCl2 = 0.8g, HCl = 18.5g

14. Example 3
If 3.2 g of CuSO4, 2.5 g of water and 3.0 g of SO2 are reacted together in the reaction:
CuSO H2O SO2  Cu H2SO4
Which reactant is the limiting reactant?
What is the mass of each of the excess reactants?

16. Example 4
700. mL of M ammonia (NH3) solution is mixed with 15.0 g of solid magnesium to produce magnesium nitride and hydrogen gas.
Which reactant is in excess?
How much (in grams) of the excess reactant remains after the reaction is complete?

18. Example 5: For the reaction:
TiO2(aq) + B4C(g) C(s)  TiB2(aq) CO(g)
If L of M TiO2, 455 g of solid carbon and 184 L of B4C gas at STP react together. Find the amount (based on the original units given) of the reactants left over.

19. Example 5: For the reaction:
2TiO2(aq) + B4C(g) C(s)  2TiB2(aq) CO(g)
If L of M TiO2, 455 g of solid carbon and 184 L of B4C gas at STP react together. Find the amount (based on the original units given) of the reactants left over.