1. Limiting & Excess Reactants
How do you know which one is which?

2. What does limiting & excess mean?
Limiting Reactant - the reactant that runs out first in a chemical reaction, thus determining the amount of product produced
Excess Reactant - the reactant that there is a quantity of left over after a chemical reaction
*The excess reactant should be the cheaper reactant since we do not like to waste unused chemical
*The excess reactant should be easy to isolate from the product(s) once the reaction is complete since we do not want contamination

3. Vinegar (5% by mass acetic acid) and Baking Soda Demo
NaHCO3 (s) + HC2H3O2 (aq)  NaC2H3O2 (aq) + H2O (l) + CO2 (g)
Flask #1
Flask #2
Flask #3
Mass of Baking Soda
1.50 g
3.50 g
5.50 g
Mass of Vinegar
50.00 g
(2.5 g HC2H3O2)

4. Outcome from Demo
Flask #1 showed the smallest amount of CO2 produced in the balloon with a clear solution in the flask.
Flask #2 showed the same amount of CO2 produced in the balloon as in flask #3, which was a larger amount compared to flask #1. The solution in the flask was still clear like in flask #1.
Flask #3 showed the same amount of CO2 produced in the balloon as in flask #2. However, the solution in the flask was cloudy.

5. Which reactant was limiting and which reactant was excess in each flask based off observations?
Baking Soda
limiting
theoretical amount
excess
Vinegar

6. The proof is in the stoichiometry
50.0 g vinegar
5 g HC2H3O2
1 mol HC2H3O2
1 mol NaHCO3
84.01 g NaHCO3
3.50 g NaHCO3
100 g vinegar
60.06 g HC2H3O2
The theoretical amount of baking soda needed to react
completely with the 50.0 grams of vinegar is 3.50 g.

7. Practice Problem 2NaI + Cl2  2NaCl + I2
1. You are given 22.1 g of NaI and 4.13 g of Cl2. What is the limiting reactant?
Pick one of the values given for your reactants and through stoichiometry find out how much you need of the other reactant.

8. You need 5.23 g to react completely with 22.1 g NaI
1 mol NaI
1 mol Cl2
70.90 g Cl2
5.23 g Cl2
g NaI
2 mol NaI
You have 4.13 g Cl2 available
You need 5.23 g to react completely with 22.1 g NaI
Therefore, Cl2 is the limiting reactant which will run out first
in the reaction and determine the amount of product produced.

9. How much NaCl is produced?
*Remember that you must always start with the limiting reactant quantity that you have because this is what determines the amount of product produced.
4.13 g Cl2
1 mol Cl2
2 mol NaCl
58.44 g NaCl
6.81 g NaCl
70.90 g Cl2
1 mol NaCl

10. How much excess reactant will be left over?
*Remember that you must always start with the limiting reactant quantity that you have because this is what determines the amount of the excess reactant you will need.
4.13 g Cl2
1 mol Cl2
2 mol NaI
g NaI
17.5 g NaI
70.90 g Cl2
1 mol NaI
You have 22.1 g available
You need 17.5 g
22.1 g NaI – 17.5 g NaI = 4.6 g NaI will be left over
after the reaction is complete

11. % Yield Chemists like to know how right we are 
% yield = (actual/theoretical) x 100
Actual  lab results
Theoretical  mathematical prediction through stoichiometry
% error = |theoretical – experimental|/theoretical x 100
% error + % yield = 100