We explain what a product is in chemistry, the process by which a product is obtained, and how to calculate the yield of a reaction.
What is a product in chemistry?
In the chemistry and its branches, it is known as a product substances obtained after a chemical reaction occurs.
In a chemical reaction two or more substances (simple or compound) are involved, called reactants or reagents, and that contribute to the reaction the atomic or molecular material that will be altered or modified during the reaction.
Once the chemical links of reagents, and generated or consumed a certain quota of Energy when the reaction occurs, we will have one or more products available.
The products that are obtained from certain types of reagents will depend directly on the conditions in which the chemical reaction occurs and on the nature of the reagents. Conditions such as temperature or presence of catalysts (other substances that affect the speed of the reaction) are decisive in the weather it takes to produce a reaction.
However, regardless of the chemical reaction considered and the conditions in which it occurs, the amount of matter and energy must be conserved, that is, the amount of reactants (atoms, molecules, ions) that react must be equal to the amount of products formed, and the energy involved at the beginning of the reaction must be equal to the energy involved at the end of the reaction, whether this energy is consumed or released in any of the reaction stages .
It is very important to understand that during a chemical reaction the amount of matter and energy in the reactants is not created or destroyed to become products, it is only transformed into them.
Yield of a reaction
In the same way, the (real) amounts of product formed are never usually identical to those considered theoretically, since this is influenced by specific properties such as the purity of the reagents or the secondary reactions that occur, as well as the environmental conditions in the reaction is generated, for example, the temperature and the humidity.
The actual product amounts (those obtained in practice and not as a result of a theoretical calculation) are less than the theoretical because, due to the above reasons, product can be lost in purification steps subsequent to the reaction, in secondary reactions where these products intervene or in evaporations if they are volatile.
The maximum amount of product that can be obtained during a chemical reaction is called the theoretical yield. To calculate the theoretical yield it is necessary to know the limiting reagent in the reaction (reagent that is exhausted first during the reaction).
The amount of actual product that is obtained in a chemical reaction is called the percentage yield.
In the following example we will see how to calculate the theoretical yield and the percentage yield of a chemical reaction, in which the limiting reagent will have to be identified.
Suppose we have the following reaction where 2.80 g of aluminum react with 4.25 g of dichlor:
There are different methods to identify the limiting reagent and it is important to clarify that the limiting reagent is not necessarily the reagent that mass has to start the reaction. We will describe two of these methods:
Method 1. It consists of calculating the amount of moles reactants using real masses and molar masses (Evil) Y M (Cl2) in this case) of each reagent. Then the actual molar ratio (quotient between amounts of substances (moles)) between the reactants is calculated, that is, using the initial masses. This actual molar ratio is then compared to the stoichiometric ratio of the reactants in the balanced equation (calculated using the stoichiometric coefficients).
It can be seen that the real ratio is greater than the stoichiometric ratio, so aluminum (whose number of moles are located in the numerator of the quotient) is in excess and dichlor is the limiting reagent.
Method 2. In this method we use the definition of a reaction mole. A reaction mole is obtained when the stoichiometric coefficients of the balanced or adjusted chemical equation react. In the reaction we are analyzing, 1 mole of reaction is obtained when 2 moles of aluminum react with 3 moles of dichlor to produce 2 moles of AlCl3, which can be represented in the following equations:
In this way, a reaction occurs more times the more moles of reaction it has. The reagent with the least amount of reaction moles is the limiting factor, since with this reagent the reaction can occur fewer times.
Using the moles of reaction and the moles of reagent, the limiting reagent can be identified as follows:
According to this method, Cl2 is also the limiting reagent, since it generates fewer reaction moles.
Once we know that dichlor is the limiting reagent, we can calculate the theoretical yield as:
Then, we convert the moles from the theoretical yield to grams, using the molar mass of AlCl3 (M (AlCl3)), and then calculate the percentage yield:
Finally, the percentage or actual yield of a chemical reaction is calculated:
And for the example we are analyzing it would be: