Which reactions are endothermic and what can be distinguished??? 5

1. Common substances to be exothermic and endothermic: exothermic: strong oxidizing acids, soluble bases, oxides to react with water (CAO, BAO, K2O, Na2O).

Endothermic: nitrate, most ammonium salts.

2. In addition to the neutralization reaction, there will be exothermic reaction, and there is also an oxidation reaction.

Exothermic reaction: a chemical reaction that emits heat, and exothermic reaction can often be manifested as an increase in the temperature of the reaction system. For example, charcoal is burned in oxygen to produce carbon dioxide, and at the same time, it also releases a certain amount of heat.

Many chemical reactions, neutralization reactions are exothermic reactions. Some exothermic reactions can only occur at a certain temperature, such as carbon does not react with oxygen at room temperature, it must be heated to a certain temperature before reacting, and the heat added does not occur in the reaction process, so do not mistakenly confuse the heat that initiates the reaction with the heat that occurs in the reaction process. In a reaction, when the energy absorbed by the molecule with average energy to the activated molecule is less than the energy emitted by the product produced by the activated molecule, the reaction is called an exothermic reaction.

The total energy of the reactant is greater than the total energy of the product. In addition to the oxidation reaction that will be exothermic, there is also a neutralization reaction.

Endothermic reactions: The chemical reactions that absorb heat during the reaction are known as endothermic reactions. Such as:

When water vapor comes into contact with hot carbon, the reaction to produce water gas is endothermic reaction. Many decomposition reactions are endothermic reactions. Heating is often used to provide the heat required for the reaction, but endothermic reactions do not necessarily have to be heated, such as the hydrolysis of salts is an endothermic reaction, and the reaction can generally occur under normal circumstances.

In a reaction, when the energy absorbed by the molecule with average energy becomes an activated molecule is greater than the energy emitted by the product of the activated molecule, this reaction is called endothermic reaction. The total energy of the reactant is lower than the total energy of the product.

Judging by the enthalpy, the enthalpy of formation of the product minus the enthalpy of formation of the reactant, if it is greater than zero, it is endothermic, and less than zero is exothermic! The enthalpy of formation of various chemicals can be checked!

There is a decomposition reaction of ammonia.

High temperatures don't necessarily trap heat, they just need temperature to initiate a reaction, like thermite.

In high school, you just need to remember that there are only typical endothermic reactions, and for ammonium ions, high temperatures are required, except for most of them, they are exothermic. If it's a university, of course, it's like the one upstairs, and it can be calculated.

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.

An endothermic reaction is a chemical reaction that absorbs heat in the process.

In a chemical reaction, a reaction in which the total energy of the reactants is greater than the total energy of the products is called an exothermic reaction.

Endothermic reactions: most of the decomposition reactions, C, Co, H2 reduction of gold Bai oxide, barium hydroxide with eight crystal 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.

The endothermic reactions are:

1. Most decomposition reactions.

2. Reaction of carbon and water vapor, C and Co, etc.

3. Hydrolysis of salts and ionization of weak electrolytes.

4. Barium hydroxide octahydrate reacts with ammonium chloride.

5. The reactions that need to be heated are endothermic reactions, but some people will misunderstand the endothermic reactions, you must know that not all reactions that require the use of catalysts are endothermic reactions, and most of the combustion reactions are exothermic reactions.

Difference Between Exothermic Reaction and Endothermic Reaction:

1. Common exothermic reactions: combustion of all combustibles, reaction of all metals with acids, all neutralization reactions, vast majority of chemical reaction reactions, minority decomposition reactions, most displacement reactions, and some metathesis reactions.

2. Common endothermic reactions: very few chemical reactions (reactions of Co and C), most of the decomposition reactions, a few displacement reactions [C+Ho(G), Fe+Ho(G)], and some metathesis reactions (reactions of ammonium salts and strong bases).

3. It can be judged according to the relative stability of reactants and products: the reaction of forming an unstable substance from a stable substance is an endothermic reaction, and vice versa is a reaction that releases energy.

Fourth, judging from the reaction conditions, all reactions that can be carried out by continuous heating are generally endothermic reactions, and vice versa, reactions that release energy.

Most of the decomposition reactions; salt hydrolysis reaction; ionization reactions; A small number of chemical reactions. An endothermic reaction is a chemical reaction that absorbs heat in the process. For example, the reaction of red-hot charcoal and water vapor to produce water gas. Only a few chemical reactions are endothermic.

1.Most of the decomposition reactions;

CaCO3 = (high temperature) CaO+CO2

cuso4·5h2o=cuso4+5h2o2.Salt hydrolysis reaction: The process of ionizing salt ions with H+ or OH- in a solution to form a weak electrolyte is called salt hydrolysis.

And the ionization balance of water is shifted in a positive direction, thereby promoting the ionization of water.

3.Ionization. 4.A small number of chemical reactions.

c(s) + CO2 (g) = (high temperature) 2CO

i2 + H2 = 2hi (this reaction is reversible because the hydrogen iodide produced is unstable).

5.Others: 2NH4Cl(S) + BA(OH)2·8H2O(S) = BACL2 + 2NH3 +10H2O

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

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

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) <>

Chemically, the chemical reaction that eventually manifests itself as absorbing heat is called an endothermic reaction. The total energy of the reactants in an endothermic reaction is lower than the total energy of the products.

The stronger the energy (bond energy) of the chemical bond in the product, the stronger the stability; The weaker the energy, the worse the stability.

For example, the C+H2O=CO+H2 decomposition reaction is generally an endothermic reaction, such as 2NaHCO3 (heating) Na2CO3+H2O+CO2Note:

Reactions that do not need to be heated are endothermic reactions, and most of the combustion reactions are "ignited", which are exothermic reactions. An endothermic reaction is a reaction that continuously absorbs a large amount of heat during chemical changes. It is not necessary that only the reactions that use a catalyst are endothermic reactions, and C+CO2=2CO is an endothermic reaction.

At the beginning of some reactions, it is necessary to provide certain conditions, such as heating, ignition, etc., once the reaction is opened, remove the conditions and the reaction continues, such a reaction is an exothermic reaction.

Sometimes as needed, indicate on the right side of the equation of the chemical reaction whether it is endothermic or exothermic, usually +q exothermic, -q is endothermic 1 Exothermic reaction: (+q) (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) Slow oxidation of substances.

6) Spontaneous redox reactions.

2 Endothermic reaction: (-q).

1) Several common reactions, such as: 2NH4Cl(S)+BA(OH)2·8H2O(S)=BACl2+2NH3 +10H2O C+H2O(G)=CO+H2 C(S)+CO2(G)=2CO Most of the decomposition reactions, such as: CaCO3=(high temperature)CaO+CO2 CuSO4·5H2O=CuSO4+5H2O Dissolution of some substances, such as ammonium nitrate dissolution, etc.

It can also be said to be the hydrolysis of salts, which must be an endothermic reaction at this time. For example, ammonium root hydrolysis is endothermy).

2) Special endothermic reactions, such as: C+CO2=2COi2+H2=2HI (this reaction is reversible, because the generated hydrogen iodide is unstable) (3) Ionization reaction. (4) Salt hydrolysis.

5) Barium hydroxide crystals are mixed with ammonium chloride crystals. (6) C is the reaction of reducing agent.