What Is a Chemical Change?

Chemical change refers to the process of atomic or electronic conversion or transfer between molecules that come into contact with each other to generate new molecules accompanied by changes in energy. The essence is the breaking of old bonds and the generation of new bonds.

Chemical changes are common in production and life. The change that produces a new substance is a chemical change. As iron

There are many types of chemical changes, which can be classified according to different aspects.

Chemical changes with characteristics;

New substances must be generated;

Exothermic glow, color change;

Emit gas and generate precipitation;

At the same time of change, physical changes occur. ^[1]

Combustion must accompany the phenomenon of light emission and heat release, but there is not necessarily a flame. If it is combustible gas, it will produce flames, such as: the combustion of hydrogen, carbon monoxide, methane, sulfur and candles will generate sulfur vapor and paraffin vapor when burning, and there is flame; but charcoal is always solid during the combustion process, and cannot be Generates flammable vapors, so there is no flame. Among them, the explosion is more complicated, there are two cases. One is the explosion caused by the heat release from combustion and volume expansion in a limited space. It is a chemical change, such as: H ₂ and O ₂ mixed ignition and explosion, firecracker explosion, etc .; the other is an explosion caused by air pressure. For example: balloon explosion, tire explosion, etc., are physical changes. Endothermic and exothermic reactions can be judged by reaction conditions. "Ignition" is exothermic; "High temperature" is endothermic. In some reactions, conditions require a "catalyst" to carry out, but no matter what reaction, the law of mass conservation must be observed.