Excess and Limiting Reactants Percent Yield

One reactant is the excess quantity and some of it will be lefy over. The second reactant is used up completely, and is the limiting reactant.

Here's the step to find the excess and limiting reactants:
Step1. Balanced equation
Step2. Convert one to another

and then you can find which one is left over. The one has more is excess reactants and the one that has less is limiting reactants

Here's a video that show an example and clearly explain about excess reactants and limiting reactants:

Percent Yield

Percent yield is the amount of product that is produced during an experiment verse the theoretical amount produced when using stoichiometry. It is simply the amount of product produced divided by the thereotical amount found by using stoichiometry then multiplied by 100% to find the percent.

If you have a theoretical value of 5 grams of water produced but only 3 grams produced when the actual experiment is done you simply divide 3 by 5 and then multiply by 100% to get a 60 percent yield.

The following video is similar to what we explain earlier:

Stoichiometry

Stoichiometry is can be thought of the ratio of moles in a chemical reaction between the reactants and products. The coefficients in a balanced equation tell you the ratios and with this you can find how much of each element or compound is produced theoretically.

For example:

2H2 + O2 -> 2H2O

If you have 10 grams of Hydrogen (H2) you can find out how much water is produced with sufficient amounts of Oxygen.


By simply converting to moles (10 grams of H2 is 10/2 or 5 moles of H2) and then transferring to the other side you will know that you get 5 moles of water and that converted to grams is (5x18=90) 90 grams.

So in one step its:

10 grams of H2 x 1mol/2grams x 2H2O/2H2 x 18 grams / 1mol of 2H2O = 90grams

Here is a video that explain stoichiometry: