1. Excess Reactant and Percent Yield

2. Excess Reactant
During a chemical reaction the limiting reactant will be all used up.
When the reaction has run its course, what will be present?
Products
Excess reactant
We will have to calculate how much of these compounds are present.

3. Percent Yield The real world does not work as perfectly as theoretical
We will never get the same amount of a product in an experiment as we have calculated using stoichiometry.
If we did we would have 100% yield.
% yield = experimental result x 100%
stoichoimetric result

4. Percent Yield and Percent Error
Are similar but not the same thing
Percent error is calculated using the difference. We want it to be 0%
We want % yield to be 100%
% error = 100% – % yield

5. Reasons for Losing Yield
Accuracy
Competing reaction
Poor technique
Poor experimental design
Impure reactants
Faulty measuring devices
Precision
Precision of instruments
Experimental technique

6. Example Al(s) + O2(g)  Al2O3(s)
10.0g of Al is combusted with 20.0L of oxygen and 12.3g of Al2O3 is produced. Calculate all theoretical values and % yield.