When weathering takes place as a result of chemical reactions, it is known as chemical weathering. In this process the rock disintegrates chemically as the chemicals in the atmospheric agents react with the chemicals of the rock and the resultant reaction brings about the weathering of the rock.
Chemical weathering involves five categories of reactions that take place and bring about the changes in the structure and composition of the rocks, namely:
The reaction takes place in a way that the free hydrogen and hydroxide ions of water replace the mineral ions to convert them in a solution. This conversion completely changes the structure of the mineral and the resultant is a clay mineral. Thus it can be said that the water ionizes and reacts with the rock minerals.
In this process, carbon dioxide is added to the rock minerals as Carbonic Acid. The carbon dioxide part of the acid is derived from the atmosphere and the flora of that particular region. Now the acid reacts with minerals like feldspar and other minerals and dissolves them, thus resulting in weathering.
This is the kind of weathering in which the water ions attach themselves to the particles of other minerals present in the rock. The attachment leads to the formation of minerals, the volumes of which are more than the volumes of original minerals, thus creating a mechanical pressure, which leads to weathering.
These oxides make the rock weak and it consequently crumbles to form smaller rock particles. This process can also be termed rusting
This is a process which is the common among all the methods of chemical weathering wherein the minerals combine with water and get washed away.
The factors that influence chemical weathering are the climate of the place, the vegetation and the physical nature of the rock. Water plays a major role as is evident from the description of methods, therefore in the absence of water, this process is nearly impossible.