Limiting Reactants and Percent Yields

Objectives:

1.    Define limiting reactant.

2.    Explain how the quantities of products are determined in a chemical reaction.

3.    Explain how to calculate the percent yield of a reaction.

Notes: (11-3)

Limiting Reactant:

The limiting reactant in a chemical equation is defined as the reactant that limits the amount of product that can be produced.  On a simpler level the concept of the limiting reactant can be applied to the practice of cooking.  Lets say that you want to make some French toast.

 The recipe that you have calls for 3 eggs, 1/4 cup of whole milk, and 6 slices of bread. In your house you currently have a loaf of bread, a gallon of milk, and 3 eggs. When you cook using a recipe the quantity of food that you are able to prepare is limited to the ingredient that you have the least of. In this situation the eggs are the limiting reactant.

Percent Yield:

The actual yield (amount of product) of a chemical reaction rarely matches the predicted yield calculated through stoichiometric calculations.  This could be due to a number of different situations including testing conditions, side reactions, and errors in recovering the products.  The calculation for percent yield is as follows:

Percent Yield = (actual yield /expected yield) x 100%