Which of the four major chemical reactions has a certain valency does not change

Metathesis reaction, because it is composed of two compounds exchanging components with each other to generate two other compounds, its essence is: the two substances that undergo metathesis reaction exchange ions with each other in aqueous solution, and combine into substances that are difficult to ionize--- precipitation, gas, water, so that the ion concentration in the solution is reduced, and the chemical reaction is carried out in the direction of the reduction of ion concentration, which does not involve valency change.

Whether it is a chemical reaction or a decomposition reaction or a displacement reaction, it actually contains a part of redox, and the valency will change.

Chemical reaction: A reaction in which two or more substances produce another substance, called a chemical reaction. 2h2+o2=2h2o

Decomposition reaction: A chemical reaction in which two or more other substances are produced from one substance is called a decomposition reaction.

2kclo3（mno2） = 2kcl＋ o2↑

Displacement reaction: The reaction of one element and one compound to produce another element and another compound is called a displacement reaction. fe＋cuso4===feso4+cu

Metathesis reaction.

There is also an acid-base neutralization reaction.

The metathesis reaction is a reaction in which two compounds exchange components with each other to produce two other compounds, which is called a metathesis reaction. Its essence is: the two substances that undergo metathesis reaction exchange ions with each other in the aqueous solution, and combine into substances that are difficult to ionize--- precipitation, gas, and water, so that the ion concentration in the solution is reduced, and the chemical reaction is carried out in the direction of the reduction of ion concentration.

It can be abbreviated as ab cd = ad cb in which the valence of each element remains unchanged before and after the valence reaction.

Metathesis reaction. The reaction of two compounds to form the other two compounds is called metathesis reaction, and the valency of each element in the reaction remains unchanged before and after the reaction.

The valency of the chemical reaction changes.

In chemical reactions, the valency of the elements must change is the chemical reaction reaction, decomposition reaction and displacement reaction, because the state of the elements in these three reactions is from elemental to compound or from compound to elemental, so the valency of the element must change.

In a metathesis reaction, the valency of an element is constant because the element is simply transferred from one compound to another.

Compound reaction is a very important type of reaction in chemistry, in which the change in valency is one of its most basic characteristics.

Valency refers to the atomic value of an element in a compound, usually expressed in Arabic numerals, such as hydrogen has a valency of +1 and oxygen has a valency of -2. In a chemical reaction, atoms form compounds by sharing or transferring electrons, so the valency also changes.

For example, when hydrogen and oxygen undergo a fusion reaction to form water, the hydrogen atom loses one electron and the oxygen atom gains two electrons, so the valency of hydrogen changes from +1 to 0, and the valency of oxygen changes from 0 to -2. The reaction formula can be expressed as: 2H2 + O2 2H2O.

However, in some chemical reactions, the valency does not change, and in this case the compound is still stable. This is because the way in which electrons are shared between atoms keeps their valency constant.

For example, when oxygen and nitrogen react to form nitrous oxide, the valency of oxygen is still -2 and the valency of nitrogen is still -3. The reaction formula can be expressed as: N2 + 2O2 2NO2.

The change in valency is closely related to the change in the energy of the chemical reaction. In some chemical reactions, the change in valency is accompanied by the release or absorption of energy. This change in energy can be used to fuel a chemical reaction or to store energy.

In conclusion, the change in valency in a chemical reaction is one of the basic characteristics of a chemical reaction, but not all of the reaction is accompanied by a change in valency. This change is closely related to the energy change of the reaction, which is of great significance for the research and application of chemical reactions.

The valence of the elements that does not change before and after a chemical reaction is a decomposition reaction, metathesis reaction, or chemical reaction.

It may be a decomposition reaction.

For example, calcium carbonate decomposes to produce calcium oxide and carbon dioxide. --

It may also be metathesis reactions and chemical reactions, and displacement reactions are not possible.

In chemical reactions, reactions in which the valency of an element does not change are: non-redox reactions.

Redox reaction: refers to a type of reaction in which the oxidation number of an element changes before and after a chemical reaction. The essence of a redox reaction is the gain or loss of electrons or the shift of shared electron pairs.

In contrast to "redox reactions", in chemical reactions, reactions in which the valency of elements does not change are called "non-redox reactions."

None of the metathesis reactions are redox reactions.

Displacement reactions are all redox reactions.

A chemical reaction with the participation of elemental elements is not necessarily a redox reaction.

For example: Fe + 5Co = Fe(Co)5, oxygen produces ozone, and the decomposition reaction with no change in valency and elemental generation is not necessarily a redox reaction.

For example, hypofluoric acid decomposes: 2HOF==2HF+O2, and the valency does not change.

Displacement reaction (one element participates and another element is generated).

The chemical reaction is not necessarily, for example, Na2O+H2O=2NaOH does not have a decomposition reaction, for example, 2NaHCO3=Na2CO3+H2O+CO2 does not.

The displacement reaction must change, because the definition of the displacement reaction is that there are elements participating in the reaction and there are elemental substances, and the elemental reaction of the reactants must become compounds, that is, the valency changes from 0 valence to other valences;Before the elemental reaction of the product, it must be a compound, that is, the valency changes from other valence states to 0 valence.

The metathesis reaction must not change because it is an exchange between ions or clusters of atoms, and since the clusters of atoms do not change, their valency does not change.

The answer is C. Because before and after the reaction of the displacement reaction, the elemental elements participating in the reaction will inevitably become compounds, and the valency will change from zero valence to non-zero valency in the compound;The compounds participating in the reaction will become elemental, and the valency will change from the valency that is not zero in the compound to the zero valence in the element. So the displacement reaction will inevitably cause a change in valency.

ca.Chemical reaction: CaO+H2O=Ca(OH)2No;O2+c=CO2 Yes (not necessarily).

b.Decomposition reaction: 2Hgo=2Hg+O2 (yes);caco3 = cao + co2 (no) (not necessarily).

c.Displacement reaction: Fe+CuCl2=Cu+FeCl2 (yes);h2+cuo=cu+h2o(have)(right)

b.Metathesis reaction: NaOH+HCl=NaCl+H2O (none), NH4HCO3+2NaOH = Na2CO3+NH3+2H2O (none).

The chemical reaction does not necessarily change (e.g., HCl+NH3=NH4Cl).

Because the chemical reaction is not necessarily a reaction from the element. But a chemical reaction with elemental involvement in the reaction must be a chemical reaction. Because the product of the chemical reaction must be a substance.

There must be a change in valency in the displacement reaction. It should be that there must be an element that becomes part of the compound, and there must be a part of the compound that becomes elemental. (To put it bluntly, there must be a transfer of electrons).

Of course, the valency of each element in the metathesis reaction (including the neutralization reaction) must not change. Because the metathesis reaction is the interaction of the ions, then combined, if they can be combined to form a difficult ionization substance, it will precipitate in the form of this difficult ionization substance, and become gas or water.

So, in general, as long as there is a transfer of electrons, there must be a change in valency.

The decomposition reaction also does not necessarily have a change in valency. (For example, potassium permanganate is decomposed by heat to produce oxygen, and there is a change in chemical addition.) Calcium carbonate is not decomposed by heat. However, the decomposition reaction is more complex, and it is not necessarily none, but only generated, there must be no change in valency. Let's say nitrite.

3hno2===hno3+2no↑+h2o

Anyway, it's annoying. When you get to high school, it's easy.

My chemistry class is very good.

Ask me any questions.

Don't forget about me hehe.

The change of valency may occur in the chemical reaction, and if there is an element participating in the reaction, it must be changed by the valency; Changes in valency may occur in the decomposition reaction, such as the formation of a single loss of chiral quality in the canopy fruit, there must be a change in valency; In the displacement reaction, because of the participation and generation of elemental elements, there must be a change in valency; In metathesis reactions, there must be no change in valency because the compounds exchange components with each other to form new compounds

Therefore, choose a balance and empty rule.