A chemical reaction is a transformation of the initial substance (reagent) into another, in which the nuclei of atoms remain unchanged, but the process of redistribution of electrons and nuclei occurs. As a result of such a reaction, not only the number of atomic nuclei does not change, but also the isotopic composition of chemical elements.
Features of chemical reactions
Reactions occur either by mixing or physical contact of reagents, or by themselves, or by raising the temperature, or by using catalysts, or by exposure to light, and so on.
Chemical processes that occur in matter are largely different from physical processes and nuclear transformations. The physical process implies the preservation of the composition, however, the form or state of aggregation may change. The result of a chemical reaction is a new substance that has special properties that are significantly different from the reagents. But it is worth noting that in the course of chemical processes, atoms of new elements are never formed: this is due to the fact that all transformations occur only in the electron shell and do notaffect the core. Nuclear reactions change the atoms of the nucleus of all elements that participate in this process, which is the reason for the formation of new atoms.
Using chemical reactions
Chemical reactions help to get almost any substance that can be found in nature in limited quantities or not at all. With the help of chemical processes, it is possible to synthesize new, unknown substances that can be useful to a person in his life.
However, inept and irresponsible impact on the environment and all natural processes with chemicals can significantly disrupt the existing natural cycles, which puts the environmental issue in the forefront and makes us think about the rational use of natural resources and the preservation of the environment.
Classification of chemical reactions
There are many different groups of chemical reactions: by the presence of phase boundaries, changes in the degree of oxidation, thermal effect, type of transformation of reagents, direction of flow, participation of a catalyst and the criterion of spontaneity.
In this article, we will consider only the group in the direction of flow.
Chemical reactions in the direction of flow
There are two types of chemical reactions - irreversible and reversible. Irreversible chemical reactions are those that proceed in only one direction and result inwhich is the conversion of reactants into reaction products. These include combustion and reactions accompanied by the formation of gas or sediment - in other words, those that proceed "to the end".
Reversible - these are chemical reactions that proceed in two directions at once, opposite to each other. In equations showing the course of reversible reactions, the equal sign is replaced by arrows pointing in different directions. This type is divided into direct and reverse reactions. Since the starting materials of a reversible reaction are consumed and formed at the same time, they are not completely converted into a reaction product, which is why it is customary to say that reversible reactions do not go to completion. The result of a reversible reaction is a mixture of reactants and reaction products.
The course of reversible (both direct and reverse) interactions of reagents can be influenced by pressure, concentration of reagents, temperature.
Forward and backward reaction rates
First of all, it is worth understanding the concepts. The rate of a chemical reaction is the amount of a substance that enters into a reaction or is formed during it per unit of time per unit volume.
Does the rate of the reverse reaction depend on any factors and can it be somehow changed?
You can. There are five main factors that can change the rate of flow of forward and reverse reactions:
- substance concentration,
- surface area of reagents,
- pressure,
- presence or absence of a catalyst,
- temperature.
According to the definition, you can get the formula: ν=ΔС/Δt, in which ν is the rate of the reaction, ΔС is the change in concentration, Δt is the time of the reaction. If we take the reaction time as a constant value, then it turns out that the change in the rate of its flow is directly proportional to the change in the concentration of the reagents. Thus, we find that the change in the reaction rate is also directly proportional to the surface area of the reactants due to an increase in the number of reactant particles and their interaction. Changes in temperature also affect the same. Depending on its increase or decrease, the collision of particles of a substance either increases or decreases, as a result of which the rate of flow of direct and reverse reactions changes.
What effect does a change in pressure have on reactants? Changes in pressure will affect the reaction rate only in a gaseous environment. As a result, the speed will increase in proportion to changes in pressure.
The effect of a catalyst on the course of reactions, including direct and reverse reactions, is hidden in the definition of a catalyst, the main function of which is just the same increase in the rate of interaction of reagents.
