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Limiting Reagent

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Reagent It is an adjective that is used to qualify what generates a reaction . In the field of chemistry , reagent is used as a noun to name the substance that establishes a link with another and that serves to reveal its presence and produce a new one.

In this sense, we can say that a limiting reagent is he who, within the framework of the reaction , he consume in its entirety . In this way, it defines the amount of product that can be formed.

Take the case of two substances that interact and produce a chemical reaction. If one of the substances is finished, since it is consumed during the process, the reaction will will stop (cannot continue to develop). The reagent consumed acts as a limiting reagent: it limits the possibility that the reaction takes its course and, therefore, also limits the amount of the product that is generated by the reaction.

It is said that the limiting reagent is based on a balanced or balanced chemical equation . It is possible to know the moles of the product obtained by knowing the number of moles of the reagent. The concept of reaction rate defines the relative amounts of products and reagents that are part of a reaction, and it is possible to express it in masses, millimoles or moles.

The mole, meanwhile, is a unity recognized by the International System of Units that serves to measure the amount of a given substance. It is worth mentioning that it is one of seven basic units (also known as fundamental physical units), which means that any of the others can be derived from these seven, which is why they are included in the set of derived units.

The limiting reagent, in short, ends and stops the reaction. At this point, those reagents that still remain, since they are only partially consumed, are called excess reagents .

The level of product obtained once all the limiting reagent is consumed marks the chemical yield of each reaction. Because of these properties , a scientist can maximize the use of reagents, using the right amount of limiting reagent and avoiding waste of resources.

This concept is of interest to the stoichiometry , he calculation of the quantitative relationships that chemistry contemplates for the products and reagents that participate in chemical reactions. It is possible to deduce these relationships from the atomic theory (which states that matter is composed of atoms, discrete units, and had its origins in Ancient Greece), although they have generally been enunciated without mentioning the composition of the subject, as observed in certain principles and laws throughout history.

It should be noted that it is not correct to think that a chemical reaction progresses to the point where its limiting reagent is consumed completely; This gives rise to two concepts: theoretical performance , the one that would take place if the product continued to form until the limiting reagent was finished; he reaction yield (or simply, the performance), which represents the actual amount of product obtained during the process.

To calculate the yield of a limiting reagent it is possible to divide the quantity obtained in reality as much as possible according to theory; if the real yield is multiplied by 100 and then divided by the theoretical one, we talk about percentage yield . It is important to note that the inequality between the reaction yield and the theoretical, for the following reasons:

* some of the products may not react;
* certain can take place side reactions that they return a different product to the desired one;
* retrieve the sample in its entirety it is almost impossible.

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