The chemical change refers to the mutual contact between molecules atom
Or electronic conversion or transfer process, generate new molecules and accompanied by changes in energy, its essence is the formation of the old bond breaking and new bond.
A total with the chemical change process Physical change
. In the process of chemical change in luminescence, usually also have the phenomenon of exothermic and endothermic. In accordance with the atom Collision theory
That intermolecular chemical changes in the collision by complete, to complete the molecular collision reaction need to meet two conditions (1) with enough energy and (2) the correct orientation. Because the reaction to overcome certain molecular energy barrier, so must have higher energy to overcome the energy barrier of molecules. Two of the collision of molecules must have the correct orientation can occur in old bond breaking.
Chemical changes The definition of the term
A chemical change ( Chemical change
) exists in the production and life. The changes of the new substance is a chemical change. Such as iron Rust
And the combustion neutralization, magnesium and so on. A macro can see all kinds of chemical changes have New material
This is a characteristic of chemical change. Summary: there are changes of the new material produced is a chemical change.
Chemical changes classification
The chemical changes of many types, which can be classified according to different aspects.
Chemical changes Type and quantity
And the resultant species and quantity were divided, can be divided into four kinds of basic chemical changes The type of reaction
: Chemical reaction
And decomposition reaction, Replacement reaction
and Double decomposition reaction
The name of the feature instance
The chemical reaction of S + O2= light =SO2
The decomposition reaction of 2H2O= power =2H2 = O2 = +
The replacement reaction H2 + =Cu + H2O CuO= high temperature
Double decomposition reaction of HCl + AgNO3 = AgCl +: HNO3
Chemical changes Change
If the reaction element valence change of point of view, can be divided into redox reaction and Non redox reaction
The redox reaction is divided into oxidation reaction
And the reduction reaction.
The essence of the redox reaction is the electron transfer or deviation. Oxidation reaction: reducing agent
(reactant), or loss of electrons Sharing a pair of electrons
To be elevated to deviate from the valence of oxidation and oxidation reaction to generate Oxidation products Reduction reaction:
The oxidant (reactant), electron or electron pairs to reduce the bias to be reduced to valence reducing reaction to generate The reduction product
Examples of redox reaction
Chemical changes Whether in ion
If the reaction is in the ion angle, can be divided into ionic and nonionic reaction reaction.
The essence of ionic reaction is certain ion concentration Change.
Chemical changes Energy change
If from the point of view of the energy change of reaction can be divided into endothermic and exothermic reaction.
Chemical changes Features
Chemical changes essence
Actually can understand the chemical change: chemical reaction
The types, the number did not change, just change the way of combination between atom and atom. For example, the molecular composition of the material, is the re combination of atoms molecules into new substances. Material Chemical property
Need chemical changes can be shown through the material, so we can use the method of physical and chemical properties of chemical reaction of substances, preparation of new material.
Chemical changes Example
Chemical changes often accompanied by light, heat, gas, precipitate or color smell change performance phenomenon, can refer to these phenomena to judge whether a chemical reaction occurs. But we should pay attention to Physical change
The difference between. Physical changes are often accompanied by light (light), heat (friction), gas (open the soda bottle, color change () oxygen
A liquid oxygen precipitates (alum), clean water), but no new substance is formed, which is the fundamental difference between physical changes and chemical changes. According to the reactant, product types can be different chemical reaction
Divided into the compound, decomposition, and replacement Double decomposition
4 basic types. But also from other angle to the classification of chemical reaction, such as oxidation into Reduction reaction
and Non redox reaction
; Endothermic reaction
and Exothermic reaction
Wait。 Nature of the object reflected in the chemical changes in chemical properties. Some chemical changes include physical change, no chemical change in a physical change.
Chemical changes The chemical forms of memory
Chemical change characteristic
The new generation of certain substances
The heat emitting color change
Gas generating precipitation
Change also changes
Chemical changes Specific examples
The combustion must be accompanied by light and heat, but not necessarily a flame.
If the flammable gas combustion, will produce flame,
Such as: hydrogen, carbon monoxide, methane combustion, sulfur and candles will be produced in combustion Sulphur vapour
There are fire and paraffin vapour;
But the charcoal in the combustion process is always solid, can not produce flammable vapor, so there is no flame.
Among them, the explosion is more complex, there are two cases.
One is due to combustion scattered away, in limited space Volume expansion
The explosion, it is a chemical change,
For example: H2 and O2 mixed light firecrackers explosion explosion, etc.;
Another is due to pressure caused by the explosion,
For example: balloon explosion, tire explosion, is a physical change.
Endothermic and exothermic reaction by reaction conditions. "Light" to "high temperature" is endothermic exothermic.
Some conditions reaction also needs "catalyst" can be carried out, but no matter what reaction, must abide by The law of conservation of mass