1. Limiting & Excess Reactants

2. Limiting Reactants – Method 1
1. Write a balanced equation.
2. For each reactant, calculate the amount of product formed.
3. Smaller answer indicates:
limiting reactant
amount of product

3. Limiting Reactants
How much product would be made if we begin with 100 g of aluminum and chlorine gas?
2 Al(s) Cl2(g)  AlCl3
100 g g x g
1 mol Al
2 mol AlCl3
x g AlCl3 = 100 g Al
3.70 mol AlCl3
27 g Al
2 mol Al Al
AlCl3
1 mol Cl2
2 mol AlCl3
x g AlCl3 = 100 g Cl2
.939 mol AlCl3
71 g Cl2
3 mol Cl2
Cl2
AlCl3
1 mol Cl2
2 mol AlCl3
133.5 g AlCl3
x g AlCl3 = 100 g Cl2
= 125 g AlCl3
71 g Cl2
3 mol Cl2
1 mol AlCl3
Cl2 is limiting and only 125 g of AlCl3 is made

4. Limiting Reactants – Method 2
Begin by writing a correctly balanced chemical equation
Write down all quantitative values under equation (include units)
Convert ALL reactants to units of moles
Divide by the coefficient in front of each reactant
The smallest value is the limiting reactant!

5. Limiting Reactants
How much product would be made if we begin with 100 g of aluminum and chlorine gas?
2 Al(s) Cl2(g)  AlCl3
100 g g x g
1 mol Al
2 mol AlCl3
133.5 g AlCl3
x g AlCl3 = 100 g Al
= 494 g AlCl3
27 g Al
2 mol Al
1 mol AlCl3 Al
AlCl3
1 mol Cl2
2 mol AlCl3
133.5 g AlCl3
x g AlCl3 = 100 g Cl2
= 125 g AlCl3
71 g Cl2
3 mol Cl2
1 mol AlCl3
Cl2
AlCl3
Cl2 is limiting and only 125 g of AlCl3 is made

6.       C3H8    +    O2    ------->     CO2      +     H2O
If you start with 14.8 g of C3H8 and 3.44 g of O2, determine the limiting reagent
b)  determine the number of moles of carbon dioxide produced
c)  determine the number of grams of H2O produced
d)  determine the number of grams of excess reagent left

7. C3H8    + 5 O2    ------->  3 CO2      +    4 H2O
a)  O2
b)  mol CO2
c)  1.56 g H2O
d)  g C3H8

8. b) Determine the number of moles of Al(OH)3 produced
  Al2(SO3)3   +  6 NaOH  > 3 Na2SO3    +  2 Al(OH)3
a) If 10.0 g of Al2(SO3)3 is reacted with 10.0 g of NaOH, determine the  limiting reagent
b)   Determine the number of moles of Al(OH)3 produced
c)   Determine the number of grams of Na2SO3 produced
d)   Determine the number of grams of excess reagent left over in the reaction

9. a) Al2(SO3)3
b)   mol Al(OH)3
c)   g Na2SO3
d)   1.84 g NaOH