1. Stoich V
Limiting Reagents

2. - Cars need tires. Every car needs 4 tires
- Cars need tires. Every car needs 4 tires. What if I only have 45 tires and 10 cars? What if there are only 6 cars and 20 tires? Which are the limiting reagents?

3. Just as in the tire problem, in chemistry, one of the reactants can be in excess and the other can be called limiting (it will run out before the other one). This limiting reagent will inhibit the amount of product being formed.

4. Example
A 2.00 g sample of ammonia is mixed with 4.00 g of oxygen.  Which is the limiting reactant and how much excess reactant remains after the reaction has stopped?
4 NH3(g) + 5 O2(g)4 NO(g) + 6 H2O(g)

5. Next we can use stoichiometry to calculate how much product is produced by each reactant.  NOTE:  It does not matter which product is chosen, but the same product must be used for both reactants so that the amounts can be compared.

6. 4 NH3(g) + 5 O2(g)4 NO(g) + 6 H2O(g)
2.00 g NH3(g)
4.00 g O2

7. Excess reactant?
Find out how much ammonia should have reacted with 4.00 g O2.
4.00 g O2
Subtract that from the original amount used.

8. Example Suppose you were given the following problem:
A 50.6 g sample of Mg(OH)2 is reacted with 45.0 g of HCl according to the reaction:
Mg(OH)2 + 2 HCl --> MgCl2 + 2 H2O