1. limiting reactant: excess reactant:
How many complete cars can be made from these available parts?
1 Complete Race Car
only 2 Engines
available:
In chemistry, the amount of product that can be made is limited by the amount of one reactant.
Image from POGIL (Flinn HSPI) Limiting Reactants
limiting reactant:
(completely consumed)
determines the amount of product formed
excess reactant:
(left over)

2. ? N2(g) + 3 H2(g) 2 NH3(g) excess limiting “left over” “runs out”
0 H2 molecules
“left over”
“runs out”
3 mol N2 is enough to make 6 mol NH3 , but…
H2 runs out after making only 2 mol NH3 .

3. Mg + 2 HCl → MgCl2 + H2 Determining Limiting Reactant
(with Math not Pics)
Determining Limiting Reactant
convert each reactant to mol of same product
the one that makes less product is LR
Which is limiting?
Mg HCl → MgCl2 + H2
48.6 g Mg g HCl
1 mol Mg
24.31 g Mg
1 mol H2
1 mol Mg
48.6 g Mg x x =
2.00 mol H2
1 mol HCl
36.46 g HCl
1 mol H2
2 mol HCl
110 g HCl x x =
1.51 mol H2
limiting
produced
1 mol HCl
36.46 g HCl
1 mol Mg
2 mol HCl
24.31 g Mg
1 mol Mg
110 g HCl x x x =
36.7 g Mg
consumed 3

4. Mg + 2 HCl → MgCl2 + H2 Determining Limiting Reactant:
(with Math not Pics)
Determining Limiting Reactant:
convert each reactant to mol of same product
the one that makes less product is LR
Which is limiting?
Mg HCl → MgCl2 + H2
48.6 g Mg g HCl
initial
–36.7 g –110 g consumed (reacted)
11.9 g Mg g HCl left over
excess
limiting
limiting
1 mol HCl
36.46 g HCl
1 mol Mg
2 mol HCl
24.31 g Mg
1 mol Mg
110 g HCl x x x =
36.7 g Mg
consumed 4

5. C2H4 + 3 O2 → 2 CO2 + 2 H2O Determining Product with LR:
How many grams CO2 can be formed from
2.70 mol C2H4 and 6.30 mol O2?
C2H O2 → 2 CO H2O
2 mol CO2
1 mol C2H4
2.70 mol C2H4 x =
5.40 mol CO2
2 mol CO2
3 mol O2
6.30 mol O2 x =
4.20 mol CO2
limiting
44.01 g CO2
1 mol CO2
4.20 mol CO2 x =
185 g CO2
produced 5

6. Quick Quiz!
1. How many grams of H2O can be formed from 64 g O2 and 3 mol H2?
2 H2 + O2  2 H2O
90.1 g H2O
72.1 g H2O
54.1 g H2O
36.0 g H2O
18.02 g H2O
1 mol H2O
3 mol H2O x =
1 mol O2
32 g O2
2 mol H2O
1 mol O2
64 g O2 x x =
4 mol H2O
2 mol H2O
2 mol H2
3 mol H2 x =
3 mol H2O
limiting