How to see if substances can react, and how to judge whether substances can react with each other

There are five main chemical reactions that are as follows:

Isomerization: (a b): The compound forms a structural recombination without changing the chemical composition.

Chemical synthesis: chemical reactions.

Abbreviation: A + B = C: Two or more elements or compounds to form a complex product. (i.e., a reaction in which two or more substances produce a new substance.) ）

Chemical decomposition: decomposition reactions.

Abbreviation: A = B + C: The compound is broken down into constituent elements or small molecules. (i.e., the reverse reaction of the chemical reaction.) It refers to the reaction in which a compound is broken down into two or more simpler elements or compounds under specific conditions. ）

Displacement reaction (monosubstitution reaction).

Abbreviation: A+BC=B+AC: Indicates an additional reactive element to replace one of the elements in the compound. (i.e., refers to the reaction of one element and one compound to produce another element and another compound.) ）

The displacement relationship is when an element that makes up a compound is replaced by an element that makes up an element. The displacement reaction must be a redox reaction, but the redox reaction is not necessarily a displacement reaction. ）

Depending on the type of elemental matter in the reactants and products, there are 4 types of displacement reactions:

The more reactive metal replaces the less reactive metal or hydrogen.

The more reactive non-metals replace the less reactive non-metals.

Non-metals replace metals.

Metals replace non-metals.

For details, see the Substitution Reaction entry ......）

Metathesis reaction (double substitution reaction).

Ab cd = ad cb: In an aqueous solution (also known as ionized), two compounds exchange elements or ions to form different compounds. (i.e., a reaction in which two compounds exchange components with each other to produce two other compounds.) )

The essence of the metathesis reaction is that the ions in the solution combine into substances that are difficult to ionize (such as water), insoluble substances or volatile gases, so that the metathesis reaction tends to be completed. The reaction between acid, alkali and salt solutions is generally formed by the exchange of components between two compounds, that is, the compounds participating in the reaction are ionized and dissociated into free-moving ions in the aqueous solution, and the ions are recombined into new compounds, so the reaction between acid, alkali and salt solutions is generally a metathesis reaction. Because the valency of each element does not change before and after such a reaction, none of the metathesis reactions are redox reactions.

Of course, there are more complex cases, but they can still be gradually simplified to be regarded as successive reactions of the above reaction categories. Chemical reactions are so varied that it is difficult to establish a simple classification standard. But some similar chemical reactions can still be classified.

Depends on whether the substance can reflect a formula, not so complicated, the true drop g= h-t* s

h refers to the enthalpy change of the reaction, s refers to the entropy change, and t refers to the temperature. When g is less than 0, it can react, when g=0, the reaction reaches equilibrium, and when g is greater than 0, it cannot react.

By the way, remember the unit conversion.

I think if you want to help the landlord explain this issue clearly, you need to know the landlord's academic qualifications, otherwise you will be more confused if you don't have enough knowledge. If you only know what the reactants are but don't have any other data or knowledge, it's completely empty to know if you can reflect it. Information about the properties of the reactants themselves, as well as the reaction conditions, is very important.

In fact, based on the usual memories and analysis, it is easy to distinguish whether the general reaction can be carried out.

If it is chemistry at the middle school level, there are some rules to follow to determine whether substances react with each other. If the force is weak, the strong acid and strong alkali produce a weak acid and weak alkali, so that it can react, and in turn, the weak acid and weak alkali cannot make a strong acid and strong alkali. It can also be judged by the relative redox strength, which is also coercive.

However, whether specific substances can react with each other depends on whether there is such a reaction in reality, and these laws cannot be used to fabricate non-existent reactions. In addition, in middle school, it is also necessary to memorize more reactions and do more questions, which can make analogies in judging whether you can react, which is also very helpful.

For example, metathesis reactions need to generate precipitation, gas, and water. This is best understood.

The reaction of salt with salt in aqueous solution is actually a reaction between ions ionized after the salt is dissolved in water. If no gas or precipitate is formed, the original ions are still present in the solution, i.e., no chemical reaction has occurred; If a gas or precipitate is formed, the ions in the solution will change, i.e., a chemical reaction will occur.

Analysis: If it is an ionic reaction, it belongs to the metathesis reaction, as long as there are insoluble substances, difficult ionization substances and volatile substances to be generated, if it is a redox reaction, generally only need to see that this substance has strong oxidation and another substance has strong reductive property and may occur after mixing, which is mainly determined by the properties of the substance, for example, nitric acid has strong oxidation, and can react with reducing substances such as: in addition to PT, Au, almost all metals can react, and there are like H2SFE2+and so on.

If it is a reaction between metals and non-oxidizing acids, just look at the activity of the metal, the metal before h can react with dilute sulfuric acid or hydrochloric acid, in the metal activity table, the metal in front can replace the metal in the back from their salt solution (k, ca, na, etc. to react with water, can not replace the metal), as long as you look at some reactions at the beginning, you can find out the law.

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Idea analysis: material reactions are often accompanied by some phenomena, which can be judged according to the phenomena. In addition, if you are familiar with the properties of matter, you can judge whether the two are reacting.

Combined with the analysis of the properties of different substances, for example, oxidizing substances are easy to react with reducing substances; Acidic substances are easily neutralized with alkaline substances, etc.

1. For metathesis reaction: see if one of these conditions is met, "there is precipitation, gas, water, and substances that are difficult to ionize (weak acid, weak alkali, etc.)".

2. For the displacement reaction: to see whether the metal activity sequence table is satisfied, the metal in front of the row replaces the metal behind it. P.S

Metal activity order table: k, ca, na, mg, al, zn, fe, sn, pb, (h), cu, hg, ag, pt, au for example: mg, fe, zn, al can replace cu2+, ag+ to generate the corresponding metals.

Whether it satisfies the strong non-metallic replacement of the weak non-metallic: for example, the non-metallic F>Cl > the base backup Br>i, so Cl2 can replace the Br in the KBR to generate Br2.

3. For redox reaction: only the oxidant can react with the reducing agent. It is necessary to remember some oxidizing fiber front cover agents and reducing agents, as well as their reducing products and oxidation products.

Chemical reactions must follow reality, and the products will not be fabricated out of thin air. By remembering the chemical reactions in the textbook, you should be able to know which reactions can be carried out and the products of which reactions. The reaction between two substances first depends on oxidation, and the one with strong oxidation reacts first, and in the same way, the one with strong metallicity reacts first, that is, whoever is strong has priority.

Next, look at solubility. Chemical reactions tend to produce more stable and insoluble substances.

S cannot react with HCI. If we can, the reaction equation is: S+2HCI=H2S+CI2

However, the oxidizing property of chlorine is stronger than that of sulfur, so sulfur cannot lose electrons, and chlorine will seize electrons of hydrogen sulfide, and the correct direction of the above chemical reaction should be from right to left; Besides, the reaction is carried out in solution, and the solubility of chlorine gas is greater than that of hydrogen sulfide (one volume of water can dissolve 400 volumes of chlorine gas, while one volume of water can only dissolve 40 volumes of hydrogen sulfide), and there will be no hydrogen sulfide gas, because after the formation of chlorine gas, chlorine gas immediately reacts hydrogen sulfide away.

To judge the strength of oxidation and metallicity, you can see it from the periodic table. In the periodic table, each column represents a family (except for the eighth group), the main group elements are required to be learned in high school chemistry, the family number is represented by Roman letters, and the letter a is written after it. In the same family, the metallicity gradually increases from top to bottom.

Each row of the periodic table represents a period, and during the same period, the metallicity of the elements gradually decreases from left to right. That is, the most metallic element in the periodic table is in the lower left corner, and the most oxidizing element is in the upper right corner.