A chemical reaction is the transformation of the starting substance (reagent) into another, in which the nuclei of the 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 by physical contact of the reactants, or by themselves, or when the temperature rises, or when using catalysts, or when exposed to light, and so on.
The chemical processes that occur in matter are significantly different from physical processes and nuclear transformations. The physical process involves maintaining the composition, but 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 during the chemical processes atoms of new elements never form: this is due to the fact that all transformations occur only in the electron shell and do not affect the nucleus. Nuclear reactions change the atoms of the nucleus of all the elements that participate in this process, which is the reason for the formation of new atoms.
Chemical reactions
Chemical reactions help to get almost any substance that in nature may be in a limited amount or not occur at all. Using chemical processes, new, unknown substances can be synthesized that can be useful to a person in his life.
However, the 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 at the forefront and makes you 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, a change in the degree of oxidation, thermal effect, the type of transformation of the reactants, the direction of flow, the participation of the catalyst and the spontaneous criterion.
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 the result of which is the conversion of reactants into reaction products. These include combustion and reactions accompanied by the formation of a gas or precipitate - in other words, those that proceed "to the end."
Reversible - these are chemical reactions that occur in two directions opposite to each other at once. In equations representing 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 do not completely turn into a reaction product, which is why it is customary to say that reversible reactions go "not completely". The result of a reversible reaction is a mixture consisting of reactants and reaction products.
Reversible (both direct and reverse) interactions of reagents can be affected by pressure, concentration of reagents, and temperature.
Forward and reverse reaction rate
First you need to understand the concepts. The rate of a chemical reaction is the amount of a substance that reacts or forms during it per unit time in a unit volume.
Does the rate of the reverse reaction depend on any factors and can it be somehow changed?
Can. There are five main factors that can change the flow rate of direct and reverse reactions:
- substance concentration
- surface area of ββreagents
- pressure,
- the presence or absence of a catalyst,
- temperature.
According to the definition, one can obtain the formula: Ξ½ = Ξ / Ξt, in which Ξ½ is the reaction rate, Ξ is the change in concentration, and Ξt is the reaction time. If we take the reaction time for a constant value, it turns out that the change in its flow rate is directly proportional to the change in the concentration of the reactants. Thus, we find that the change in the reaction flow rate is also directly proportional to the surface area of ββthe reactants due to an increase in the number of reactant particles and their interaction. A similar effect is affected by temperature changes. Depending on its increase or decrease, the collision of particles of a substance either increases or decreases, as a result of which the flow rate of direct and reverse reactions changes.
What is the effect of the change in pressure exerted on the reactants? Changes in pressure will affect the reaction rate only in a gaseous medium. As a result, the speed will increase in proportion to changes in pressure.
The influence of the catalyst on the course of reactions, including direct and reverse, is hidden in the definition of a catalyst, the main function of which is just the same increase in the rate of interaction of the reactants.