chemical reaction is the process of transformation of substances, during which time there is a change in their structure or composition.As a result of this process is a transition starting materials or reagents into the final products.To date, it formed a very clear classification of chemical reactions.
Description reactions using equations.Signs of chemical reactions
There are several classifications, each of which takes into account one or more features.For example, chemical reactions can be separated by paying attention to:
- quantity and composition of the reagents and the final products;
- aggregate state of the initial and final substances (gas, liquid, solid form);
- number of phases;
- nature of the particles, which are transferred in the reaction (ion, electron);
- thermal effect;
- possibility of reaction in the opposite direction.
It should be noted that the chemical reaction is usually written with the help of formulas and equations.The left side of the equation describes the structure of the reactants and the nature of their interaction, and the right side you can see the final product.Another very important point - the number of atoms of each element on the right and left side should be equal.Only in this way it respected the law of conservation of mass.
As already mentioned, there are many classifications.It will discuss the most commonly used.
Classification of chemical reactions on the composition, the number of initial and final products
reactions compounds: they enter more substances are combined to form a more complex substance.In most cases, this reaction is accompanied by heat.
decomposition reactions: starting reagent is a complex compound which forms in the process of disintegration of several simpler substances.Such reactions may be either redox or occur without changing the valence.
Substitution reactions - is the interaction between complex and simple substance.The process is a replacement of an atom of a compound.Schematically, the reaction can be displayed as follows:
A + BC = AB + C
Reactions exchange - a process during which the two original reagent exchanged between the constituent parts.For example:
AB + CD = AD + CB
transfer reactions - are characterized by the transfer of an atom or group of atoms from one substance to another.
Classification of chemical reactions: reversible and irreversible processes
Another important characteristic of reactions - is the ability to reverse the process.
So called reversible such reaction products which may interact with each other, forming the same starting materials.As a rule, in the equation have to be displayed this trait.In this case, the left and right part of the equation put two opposing arrows.
in irreversible chemical reaction products it is not able to react with each other - at least under normal conditions.
Classification of chemical reactions on the thermal effect
thermochemical reaction is divided into two main groups:
- exothermic processes, during which there is heat (energy);
- endothermic processes that require the absorption of energy from the outside.
Classification of chemical reactions on the number of phases and phase featured
As mentioned, the physical state of matter is also of great importance for the complete characterization of the chemical reaction.On these grounds usually distinguished:
- gas reactions;
- reaction solution;
- chemical processes between solids.
But the initial and final products do not always refer to any one state of aggregation.Therefore, the reaction and classified according to the number of phases:
- single phase or homogeneous reactions - a process, the products are in the same state (in most cases, the reaction proceeds in either gaseous phase or in solution);
- heterogeneous reactions (multiphase) - reagents and the final products can be in different states of aggregation.
