Is it an exothermic reaction, or an endothermic reaction

If you want an answer, it is: most chemical reactions are exothermic reactions, for example: for example, many combustion reactions are chemical reactions, which belong to exothermic reactions

First, common exothermic reactions include: 1. Combustion phenomenon; 2. Most chemical reactions are exothermic reactions. 3. Reaction between metal and acid; 4. The neutralization reaction of all strong acids and strong bases (strictly speaking, weak acids and weak bases are also counted, but because the exothermic phenomenon is not obvious, middle schools generally do not get them).

Second, the common endothermic reactions include: 1. Chemical reactions with ammonium salts - such as Ba(OH)2+NH4CI in textbooks and other ammonium salts such as NH4NO3 or NH4HCO3 (the main component of chemical fertilizers), such as homemade travel "ice packs" are used to react with sodium carbonate and ammonium nitrate to absorb heat, so ammonium salts and alkali or acid salts can absorb heat; 2. Most of the decomposition reactions, such as the laboratory preparation method of O2 in textbooks. Generally, the decomposition reaction that needs to be heated is also an endothermic reaction; 3. There is also a typical reaction between red-hot carbon C and CO2 or H2O (the former is a chemical reaction).

Endothermic reactions: most of the decomposition reactions, C, Co, H2 reduction of metal oxides, barium hydroxide with eight crystalline water and ammonium chloride reaction, most of the salt hydrolysis reactions, a few chemical reactions (generally not required to master) exothermic reactions: most of the chemical reactions, acid-base neutralization reactions, metal and acid reactions, metal and water reactions, combustion reactions, ** reactions, there should be no problem in mastering these questions, I hope it will help you!

The exothermic and endothermic reactions are as follows:

An exothermic reaction is the release of heat, which is the process of releasing heat, i.e., the temperature of the surrounding gas will increase accordingly, and the object (the exothermic object) may heat up. The representative reaction types are: combustion (oxidation), neutralization. The equation for the exothermic reaction: δh<0.

The endothermic reaction is the process of absorbing heat, that is, the temperature of the surrounding gas will decrease accordingly, and the object (the endothermic object) may cool down. Representative reaction types are: calcium carbonate decomposition, carbon and carbon dioxide reaction, barium hydroxide crystal reaction with ammonium chloride, hydrolysis.

The equation for endothermic reaction: δh> 0.

Methods for judging exothermic reactions and endothermic reactions:

1. Judge according to the relationship between the total energy of the reactant and the total energy of the product.

2. Judge according to the relationship between the sum of bond energy of reactants and the sum of bond energies of products.

3. Judge according to the basic type of chemical reaction.

4. Combustion, neutralization, metal oxidation, thermite reaction, more active metal and acid reaction, and most of the chemical reactions from unstable substances to stable substances are exothermic (but it should be noted that the transformation of graphite into diamond under high pressure is an exothermic reaction, although it is the opposite under normal pressure).

5. Most decomposition reactions are endothermic (but none can be absolute, such as potassium chlorate decomposition to produce potassium chloride and oxygen is a common exothermic reaction) can be spontaneously carried out redox reactions are exothermic reactions, common reactions in combustion reactions, neutralization reactions are all exothermic reactions, acid-base neutralization reactions, metal and acid reactions, metal and water reactions, combustion reactions.

**The reaction is all exothermic reactions, and it is often necessary to combine the facts in memory in specific judgments. The reverse reaction of an exothermic reaction must be an endothermic reaction.

1. Decomposition reaction - endothermic reaction.

The decomposition reaction is generally an endothermic reaction, such as sodium bicarbonate is decomposed into sodium carbonate, water and carbon dioxide when heated; Calcium carbonate can be decomposed into calcium oxide and carbon dioxide under high temperature conditions.

2. A small number of chemical reactions - endothermic reactions.

For example, carbon and carbon dioxide react at high temperatures to form carbon monoxide, which is an endothermic reaction.

3. Combustion reaction - exothermic reaction.

The combustion reaction usually occurs when hydrocarbons react with oxygen to produce carbon dioxide and water. The combustion reaction is a process in which the combustible components in the mixture react sharply with oxygen to form a flame that emits a large amount of heat and intense light.

4. Neutralization reaction - exothermic reaction.

Acid-base neutralization is a reaction in which acids and bases exchange components with each other to produce salt and water, and heat is released. The essence of the neutralization reaction is that hydrogen ions and hydroxides combine to form water, or acids and bases react to form salts and water.

5. Thermite reaction - exothermic reaction.

The thermite method is a method that uses the reducibility of aluminum to obtain high melting point metal elements. It can be simply thought of as the reaction of aluminum with certain metal oxides (such as ferric oxide, chromium trioxide, manganese dioxide, etc.) under high thermal conditions. The thermite reaction is often used to smelt metals with high melting points, and it is an exothermic reaction in which magnesium strips are the ignition agent and potassium chlorate is the accelerant.

Exothermic reactions: combustion of combustibles; acid-base neutralization reaction; Most chemical reactions; Metal and acid displacement reaction; slow oxidation of substances, etc. Endothermic reaction:

Most of the decomposition reactions; hydrolysis of salts and ionization of weak electrolytes; Ba(OH) reacts with NH4Cl; Reaction of carbon and water vapor, C and CO2, etc.

Heat of reaction of the neutralization reaction:

The heat emitted by the acid-base neutralization reaction.

Heat of neutralization: In dilute solution, the amount of heat neutralization heat released when acid and base are neutralized to form 1 mol of water is independent of the amount of reactants.

Enthalpy: The energy possessed by the substance itself is expressed in enthalpy.

Symbol: H enthalpy change H = h product - h reactant.

When h<0, it is an exothermic reaction.

When h>0, it is an endothermic reaction.

Factors influencing enthalpy and the magnitude of enthalpy.

1. Different substances, H is different, H is also different.

2. The same substance, the larger the amount of the substance, the greater the h, the greater the h 3. For the same substance, h (gas) > h (liquid) > h (solid) enthalpy change is different from the heat of reaction

The size of h depends on the symbol, and the size of q does not depend on the symbol.

Comparison of exothermic and endothermic reactions.

Common exothermic reactions:

1) All combustion or ** reactions.

2) Acid-base neutralization reaction.

3) Most of the chemical reactions.

4) The reaction of active metals with water or acid to form H2.

5) Many redox reactions (but not absolute). For example, hydrogen, charcoal or oxygen turbine carbon reduction copper oxide are typical exothermic reactions.

6) NaOH or concentrated sulfuric acid dissolved in water (note: these two points only say that they will be exothermic, but strictly speaking, they are not considered chemical reactions, and should be paid attention to during the exam).

Common endothermic reactions:

1) Most decomposition reactions:

CaCO3 = (high temperature) CaO+CO2

The relative magnitude of the total energy of the reactants and the products of the endothermic reaction.

The relative magnitude of the total energy of the reactants and the products of the endothermic reaction.

CuSO4·5H2O=CuSO4+5H2O2), salt hydrolysis reaction.

3) Ionization.

4) A small number of chemical reactions.

c(s)+CO2(g)quiet=(high temperature)2COi2+H2=2Hi (this reaction is reversible, because the generated hydrogen iodide is unstable)5), others:

2nh4cl（s）+ba（oh）2·8h2o（s）=bacl2+2nh3↑+10h2o

c + H2O (g) = (high temperature) CO + H2

In general, the following reactions are exothermic reactions:

1.Combustion of combustibles (exothermic, for sure).

2.Acid-base crack shouts and (definitely exothermic).

3.The metal reacts with the acid.

4.The reaction conditions are:"Ignition at the source of ignition"such as the combustion of iron in chlorine gas.

In general, the following reaction is endothermic reaction:

1.The reaction conditions are:"Heating"

2.The reaction conditions are:"High temperatures"

3.Some special reactions, such as the mixed grinding of macroridge ammonium chloride solids with barium hydroxide crystals.

The above generalization is just"General", in which some special reactions will also occur, such as:

Fe + S = Heating = Fes

This reaction is conditioned on:"Heating", but the reaction itself is an exothermic chemical reaction.

The endothermic reactions and exothermic reactions that junior high school requirements to know mainly include:

1. All combustion reactions (exothermic reactions).

2. The reaction between acid and metal (filial piety exothermic reaction).

3. Reaction (exothermic reaction) with metal oxides

4. All slow oxidation, such as iron rusting, brewing, food decay, and the respiration of people and animals and plants, etc., should be cautious. (exothermic reaction).

5. CaO+H O==Ca(OH) (exothermic reaction) 6. Co+C=2Co (endothermic reaction).

7. Caco = Cao + Co (endothermic reaction) <>