Question 6: Why the actual yield is usually less than the theoretical yield of a reaction?
Theoretical Yield: The quantity of product (in moles or grams) obtained when the limiting reagent is completely converted (consumed). This amount of product can be produced in 100% efficient reactions.
Actual yield: It is the amount of product obtained actually in the experiment. This is also called experimental or practical yield.
Actual yield of a reaction is less than the theoretical yield
It is found that the actual yield of a chemical reaction is always less than the experimental yield. The reasons for such decrease are many. However, some more frequent reasons are given below.
- The reaction is reversible and due to reversibility of the reaction, all reactants may not have converted into products.
- There may be a parallel or chain reaction and some of the reactants may have converted to some other product.
- Usually it is difficult to recover all the products of the reaction. This makes the quantity of the product reduced. This is called mechanical loss of the product.
- Reaction conditions, like pressure and temperature, may have disturbed.
This is therefore, suggested to the chemists to check the efficiency of the reaction in terms of percentage yield.
Percentage yield: It is the percent of ratio of actual yield to theoretical yield. It tells us, for example, if we actually obtain 80 g of the product in a chemical reaction and theoretically (on the basis of calculation) it should be 100 g, then the percentage yield is 80 g.