How can you tell the change in the energy of a chemical reaction?

1) Exothermic, endothermic reactions are related to the bond energy of the substance, but it cannot be linked to the mass. This is a chemical change, which is a reaction between atoms and does not involve the inside of the atoms. The mass change occurs during a nuclear reaction, so the two are unrelated.

2) Why do some chemical reactions emit heat, while others need to absorb heat? This is due to the fact that the energy possessed by various substances is different. If the total energy of the reactant is higher than the total energy of the product, then when a chemical reaction occurs, a part of the energy will be converted into heat energy and other forms of release, which is an exothermic reaction.

If the total energy possessed by the reactant is lower than the total energy possessed by the product, then when a chemical reaction occurs, the reactant needs to absorb energy to convert into the product, which is an endothermic reaction. It can be seen that the process of chemical reaction can also be regarded as the process of converting the energy "stored" in the substance into heat energy and being released, or the heat energy being converted into the energy inside the substance and being "stored".

To determine or measure the heat of reaction, you can use a calorimeter, which is an instrument that measures the physical or chemical effects of a sudden occurrence, that is, it can measure the change in the heat capacity of a substance (including the heat of reaction).

In terms of the type of reaction: the following four types of reactions are exothermic reactions.

1) Acid-base neutralization reaction.

2) Reactive metals react with acids.

3) Combustion reaction of combustibles.

4) Most chemical reactions.

Change in energy in a chemical reaction: The change in the heat of a chemical reaction.

Chemical reaction. The main forms of change in the residual capacity of the medium energy:

Chemical energy vs thermal energy.

Chemical energy and electrical energy of skin destruction mode.

Chemical energy vs light energy.

The reason for the energy conversion of chemical reactions: The essence of chemical reactions is the chemical bonds in the reactant molecules.

Breakage, the process of forming new chemical bonds The breaking of old bonds requires the absorption of slow energy, and the formation of new bonds requires the release of energy.

In general chemical reactions, the total energy absorbed by the breaking of the old bond is not equal to the total energy released by the formation of the new bond, and this difference is the change of energy in the reaction, so there will be a change in energy during the chemical reaction.

In electrochemistry, chemical energy is converted into electrical energy, in thermochemistry, chemical energy is converted into internal energy, which is transferred in the form of heat, and in biochemical reactions, biological energy is converted into chemical energy, which is eventually lost in the form of heat.

It can be judged according to the type of reaction, heat change, bond energy, and common reactions, as follows.

1) Exothermic reaction:

The total energy possessed by the reactant The total energy possessed by the product.

The sum of bond energies of the reactants The sum of bond energies of the products.

Stability: reactant product (the lower the energy, the more stable the principle) h 0, that is, h is " ".

Typical reactions: general combustion, neutralization reaction, reaction between active metal and dilute acid, thermite reaction, conversion from unstable substance to stability, oxidation of metal, most chemical reactions, etc.

2) Endothermic reaction:

The total energy possessed by the reactant The total energy possessed by the product.

The sum of bond energies of the reactants The sum of bond energies of the products.

Stability: Reactant product.

h 0, i.e. h is " ".

Typical reaction: C (scorching) Co

2. Calcined limestone, water gas, BA (OH).

8HO with NH

CL reactions, ionization of weak electrolytes, hydrolysis of salts, conversion from stable to unstable substances, most decomposition reactions, etc.

Hope it helps.

Depending on the reaction conditions, the total energy of the product is greater than the total energy of the reactant when heated. The second is to judge whether it is exothermic or endothermic, and the total energy of the product is greater than the total energy of the reactant. Endothermic is the opposite.

The change in energy in a chemical reaction usually manifests itself as a change in heat. The heat of combustion and the heat of neutralization refer to the heat emitted when the stable oxide is completely burned and the heat of the reaction when the neutralization reaction is used to form 1 mol of water.

In chemistry, there is also Geis's law, the heat of reaction of a chemical reaction is only related to the initial state and the final state of the reaction, and not to the pathway of the reaction. The characteristic of chemical reaction is that new substances are generated, and the total energy of new substances and reactants is different, and the energy of each substance is different. **The essence of exothermic and endothermic chemical reactions should always be paid attention to.

There are thermal changes in energy changes in chemical reactions: endothermic reactions and exothermic reactions. heat of combustion and heat of neutralization; Heat of combustion:

At 101 kPa, 1 mol of combustibles is completely burned to form a stable oxide. Heat of neutralization: In a dilute solution, the heat of reaction when the neutralization reaction of acid and base occurs to produce 1mol of water.

The relationship between the change of the gas, liquid, and solid states of a substance and the heat of reaction.

1. Common endothermic reactions: hydrolysis of salts, ionization of weak electrolytes, most decomposition reversal 2 special chemical reactions N2 + O2 = discharge = 2NO CO2 + C = high temperature = 2co Two special displacement reactions C(S) + H2O(G) = high temperature = Co (G) + H2 (g) Cuo(s) + H2(G) = high temperature = Cu (S) + H2O(G) Ba (Oh) 2·8H2O crystal reaction with NH4Cl crystal Dissolution of ammonium nitrate (physical change, endothermic phenomena).

2. Common exothermic reactions, combustion, neutralization reactions, metal reactions with acids or water, general chemical reactions (except for the above two special cases) focus on three balances: N2, H2 synthesis NH3, SO2 catalytic oxidation to generate SO3, NO2 dimerization to N2O4 are exothermic reactions, general displacement reactions (except for the above two special cases) basic oxides (such as Na2O, K2O), strong alkali soluble in water, dilution of concentrated sulfuric acid (physical change exothermic phenomenon) most oxidation.

People realize in production and life that almost all chemical changes are accompanied by energy changes. The change in energy in a chemical reaction usually manifests itself as a change in heat. Energy changes include exothermic, endothermic, luminous, discharge, etc.

The old chemical bond is broken, the new chemical bond is formed, the bond is broken to absorb energy, and the new bond is formed to release energy, so the reaction process must be accompanied by energy changes, the form of energy changes is mainly heat changes, but also energy changes in the form of light energy, electrical energy, etc., chemical reactions are either endothermic reactions or exothermic reactions, so chemical reactions must be accompanied by changes in heat correctly.

Chemical reactions are characterized by the formation of new substances, and the total energy of new substances and reactants is different, because the energy possessed by each substance is different.

The essence of energy conservation in the reaction is that the energy released by the formation of new chemical bonds is greater than the energy of the old chemical bond breakage and is released in the form of other energy.

If the total energy possessed by the reactant is higher than the total energy generated, then a part of the energy will be released in the form of heat energy in the reaction, which is an exothermic reaction, and vice versa, an endothermic reaction.

1. The essence, characteristics and laws of chemical reactions: substance: the breaking of the chemical bonds of reactants and the formation of chemical bonds of products.

Characteristics: There is both the generation of new matter and the change of energy. Laws to follow:

Conservation of mass and conservation of energy. 2. The form of energy in the process of chemical reaction: it is often expressed in the form of heat energy, electrical energy, light energy, etc.

The change in energy in a chemical reaction usually manifests itself as a change in heat. **The essence of exothermic and endothermic chemical reactions should pay attention to four points: Chemical reactions are characterized by the formation of new substances, and the total energy of new substances and reactants is different, because the energy of each substance is different (the essence of chemical reactions is the breaking of old chemical bonds and the formation of new chemical bonds, and the energy absorbed by the breaking of old chemical bonds is different from the energy released by new chemical bonds, resulting in energy changes); The essence of energy conservation in the reaction is that the energy released by the formation of new chemical bonds is greater than the energy of the old chemical bond breakage and is released in the form of other energy. If the total energy possessed by the reactant is higher than the total energy generated, then a part of the energy will be released in the form of heat energy in the reaction, which is an exothermic reaction, and vice versa, an endothermic reaction. It can be represented by an image.