Product in Chemistry
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 chemistry and its branches, the substances obtained after a chemical reaction occurs are known as products.
In a chemical reaction, two or more substances (simple or compound) intervene, 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 bonds of the reactants are modified, and a certain amount of energy is generated or consumed when the reaction occurs, we will have one or more products available.
The products that are obtained from a certain type 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 the presence of catalysts (other substances that affect the speed of the reaction) are determining factors in the time it takes for a reaction to occur. What is it Adjective, concept, examples
However, whatever 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 start 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 stages of the reaction.
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 specific properties such as the purity of the reagents or the secondary reactions that occur, as well as the environmental conditions in the environment, influence this. reaction to occur, for example, temperature and humidity.
The actual amounts of product (those obtained in practice and not as a result of a theoretical calculation) are lower than the theoretical ones 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 reactant in the reaction (reactant that is exhausted first during the reaction).
The amount of actual product obtained in a chemical reaction is called the percent 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 reactant must be identified.
Suppose we have the following reaction where 2.80 g of aluminum react with 4.25 g of dichloro:
There are different methods to identify the limiting reactant and it is important to clarify that the limiting reactant is not necessarily the reactant with the greatest mass at the start of the reaction. We will describe two of these methods:
Method 1. It consists of calculating the number of real moles of the reactants using the real masses and the molar masses (M(Al) and M(Cl2) in this case) of each reactant.
Then, the real molar ratio (ratio 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 actual 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 dichloro is the limiting reactant.
Method 2. In this method we use the definition of mole of reaction. One mole of reaction is obtained when the stoichiometric coefficients of the balanced or balanced 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 dichloro to produce 2 moles of AlCl3, which can be represented by the following equations:
In this way, a reaction occurs more times the more moles of reaction it has. The reagent with the least number of moles of reaction is the limiting one, since with this reagent the reaction can occur fewer times.
Using the moles of reaction and the moles of reactant, the limiting reactant can be identified as follows:
According to this method, Cl2 is also the limiting reagent, since it generates fewer moles of reaction.
Once we know that dichloro is the limiting reagent, we can calculate the theoretical yield as:
Finally, the percentage or actual yield of a chemical reaction is calculated:
And for the example we are analyzing it would be:
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