Why is it necessary to exothermic for the formation of chemical health, and must the chemical reacti

Let's give you a visual explanation.

When a chemical bond is formed, the distance between atoms or molecules is reduced, and they are bound by a force.

So think about it, if the distance between 2 objects becomes smaller, do they release energy, or absorb energy? - Giving off energy, of course. Because of the conservation of energy.

Correspondingly, if two objects that were originally a certain distance are now made more apart, do they absorb energy or release energy? - Absorbing energy, of course. It's as if two big men are twisted together, and it takes force to separate them.

To study chemistry, you must have visual thinking, and you can also think of a way to understand and memorize it yourself.

Think about it the other way around.

Since it is a chemical bond, it is definitely present in a stable compound. If you want to break a chemical bond, you need energy, so the formation of a chemical bond is the release of energy.

The unstable energy is higher, the stable energy is lower, the two unstable synthetic stable energy decreases, and the excess energy is of course released.

There is a difference in the bond energy of each bond, if it is a substance with high bond energy and a substance with relatively low bond energy, a certain energy difference will be formed in the middle, so as to release energy, if the energy is lower and the formation is higher, it will absorb energy, and there is almost no constant, but the general reaction of exergation must first absorb a certain amount of energy, and it can only be carried out if certain conditions are met.

1. The hydride formation reaction is an exothermic reaction.

For example, hydrogen and fluorine are exothermic in the dark: H2 +F2 = 2HF2, and the formation of oxides is an exothermic reaction.

For example, charcoal is burned in air or oxygen to exothermic: C+O2 = CO23, the formation of oxygenated acids.

For example, sulfur trioxide dissolved in water to form sulfuric acid is an exothermic reaction: SO3 + H2O = H2SO44, and the formation reaction of strong alkali is an exothermic reaction.

For example, sodium oxide reacts with water to form sodium hydroxide and is exothermic: Na2O+H2O=2NaOH<>

Common types of endothermic reactions:

1. Most decomposition reactions:

CaCO3 = (high temperature) CaO+CO2

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

3. Ionization. 4. A small number of chemical reactions: C (S) + CO2 (G) = (high temperature) 2Coi2 + H2 = 2Hi (this reaction is a reversible reaction because the generated hydrogen iodide is unstable) 5. Others: the relative size of the total energy of the reactants and products of the endothermic reaction c + H2O (g) = (high temperature) CO + H2

The above content refers to Encyclopedia - Exothermic Reaction.

Encyclopedia—endothermic reactions.

Exothermic chemical reactions refer to chemical reactions that emit heat during the reaction.

An exothermic chemical reaction releases energy so that the energy of the reactants is lower than before the reaction and the energy of the products is lower than before the reaction. Exothermic reactions usually have a significant temperature increase, and experimental equipment such as a calorimeter can also be used to measure the temperature change before and after the reaction and the amount of heat released.

Exothermic reaction is a chemical reaction that occurs in nature and industry, through the use of exothermic reaction, people can obtain a certain substance or energy, such as energy from fuel, water heating or air conditioning and refrigeration. In industrial production, exothermic reaction is also widely used, such as the production process of chemical fertilizers, polyester, paraffin, etc.

Acid-base reactions are also common exothermic reactions, which use heat energy to promote the formation or decomposition of reactants to release energy. For example, when hydrochloric acid and sodium hydroxide react, a large amount of heat will be released, resulting in an increase in the temperature of the reaction solution. Similarly, redox reactions can also be exothermic reactions, such as when iron reacts with acid, it releases a large amount of heat energy.

Points to note for exothermic reactions:

1. Safety: The heat released by the exothermic reaction is very large, and the safety issues that need to be paid attention to are not limited to the high temperature and high pressure factors generated in the reaction process, but also take into account the characteristics of the reaction substance, accidents and other factors to ensure the safety of the reaction process and avoid damage to personnel and the environment, so it is necessary to maintain sufficient air ventilation and safety protection equipment during the reaction process.

2. Temperature destruction and energy utilization: The heat generated by the exothermic reaction may lead to an increase in the temperature and fiber of the reaction and an acceleration of the reaction rate, so it is necessary to control the reaction temperature during the reaction process to avoid the danger caused by the rapid and violent reaction. The heat generated by exothermic reactions can be utilized, for example, for heating, power generation, energy storage, etc.

3. Technical requirements: Different exothermic reactions have different technical requirements, and it is necessary to master the appropriate reaction conditions and operation skills according to the characteristics of the specific reaction substances and the characteristics of the reaction process, so as to ensure the smooth progress of the reaction and get the desired results. There are different technical control requirements for different types of exothermic reactions.

Not necessarily. A chemical reaction is a reaction in which two or more substances react to form a new substance, some of which are redox reactions and some are non-redox reactions. In addition, chemical reactions generally release energy.

Chemical reaction: One of the reactants is O2

Magnesium burns in the air [2mg+o2==ignition==2mgo].

Iron burns in oxygen [3Fe + 2O2 = = Ignition = = Fe3O4].

Aluminum burns in the air (or slowly oxidizes on the surface) [4Al+3O2==Ignite==2Al2O3].

Precautions for chemical reactions.

If the concept is not clear, the principle is not clear, and the law of change of matter is not very clear, the question will be wrong. For example, if the relative molecular weight of H2O is only the relative molecular weight of one chemical formula, such as H2O with a relative molecular weight of 18, the relative molecular weight of water in 5H2O is still 18 instead of 90. Another example is that the relative molecular mass ratio of C and D in A+2B=C+2D is known to be 22:

9。If 4 grams of C are generated, how many grams of D are generated at the same time?where the mass ratio of c and d must be 22:2 9=22:

18, and then proceed with the relevant calculations. It would be a mistake to calculate the mass ratio of c and d at 22:9, reflecting that you do not know the difference between relative molecular weight and mass.

The molecules formed by the interaction between atoms (ions) to form chemical bonds are more stable than atoms, and the energy of the system is reduced, so energy is released.

The energy of the so-called state is the various particles in the atom or molecule (e.g., the electron, the nucleus. The sum of all the energies. For example, the potential energy of the electrons in a covalent compound molecule attracted to two nuclei is lower than that of an atom when it is attracted to one nucleus, and the increase in the range of electrons in the fascicle macron also reduces its kinetic energy (delocalization effect).

Why are some chemical changes exothermic while some chemical changes are endothermic.

Because chemical energy is converted into heat energy.

When the chemical changes, the chemical energy of the product is higher and it will absorb heat, and the chemical energy of the product will be low and it will be exothermic, and the more unstable the substance, the greater the chemical energy and the smaller the bond energy.

The bond energy corresponding to the molecular reaction, the state of the bond energy of the Shengfan Xinghu is also exothermic when the state of the bond energy is large, and the sum of the bond energy is endothermic when it becomes smaller.

Later, when you learn about enthalpy change in college, you will understand that enthalpy decreases heat release, and enthalpy increases heat absorption.

1) Changes in matter and energy in chemical changes.

The essence of the change of matter (chemical and chemical reactions): the breaking of old chemical bonds and the formation of new chemical bonds.

The essence of energy change: the destruction of old chemical bonds requires the absorption of energy, and the formation of new chemical bonds requires the release of energy.

3) Whether a chemical reaction absorbs or releases energy depends on the relative magnitude of the total energy of the reactants to the total energy of the products.

Exothermic reaction and endothermic reaction: The reaction that releases energy during a chemical reaction is called an exothermic reaction; The reaction that absorbs energy during a chemical reaction is called endothermic reaction.

Exothermic reaction. Endothermic reaction.

Manifestations. h 0 or h is " ".

h 0 or h is " ".

Energy changes. Total energy released by the product The total energy absorbed by the reactant.

Total energy released by the product The total energy absorbed by the reactant.

The bond energy changes. Total bond energy of the product Total bond energy of the reactant.

Total bond energy of the product Total bond energy of the reactant.

Contact. The greater the bond energy, the lower and more stable the material energy, and vice versa, the smaller the bond energy, the higher the material energy and the more unstable.

The energy released or absorbed in the process of chemical reaction can be expressed in terms of heat (or converted into corresponding heat), which is called anti-bridge Li heat.

A Some exothermic chemical reactions need to be heated to occur, such as thermite reactions, so A is wrong; Some endothermic reactions will also occur without mold heating, such as the reaction of ammonium chloride and barium hydroxide crystals, so b is wrong;

c The chemical reaction must be accompanied by the change of energy such as luminescence and heat generation when the material changes, so C is correct;

d The total energy of the reactant is not equal to the total energy of the product, such as an exothermic reaction, the total energy of the reactant is greater than the total energy of the product, so D is wrong

Therefore, C