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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.

  1. The reaction is reversible and due to reversibility of the reaction, all reactants may not have converted into products.
  2. There may be a parallel or chain reaction and some of the reactants may have converted to some other product.
  3. 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.
  4. 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.


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