Chemical weathering refers to the decomposition of rock to create a new chemically different material. To understand chemical weathering, it is essential to understand the chemical properties of raw materials. The prime agents involved in chemical weathering are the gases in the atmosphere- Oxygen, Carbon Dioxide, and other gases along with the water from precipitation in the form of rain and snow. During a chemical weathering process, the internal molecular structure of a mineral is altered by a reaction with other elements to form a different element. For example, dissolved oxygen in water oxidises minerals containing iron through oxidation.
Read More: Biological Weathering
Chemical Weathering Definition
The process of decomposing rocks and soil chemically is known as chemical weathering. Chemical Weathering is the process through which the rock interacts with chemicals to change its composition of the rock. Rocks are dissolved or reduced to a fine condition by chemical weathering processes like dissolution, solution, carbonation, hydration, oxidation, and reduction.
Chemical Weathering Processes
- Due to denudation and other similar processes, they reach the surface after forming inside the Earth’s crust for millions of years.
- Once they are above ground, they encounter various ecological elements including air, water, etc.
- These elements influence how the Rocks evolve. Physical Weathering or chemical weathering are both examples of this.
- Due to a chemical reaction occurring on the rocks, chemical weathering modifies the structure of the rocks.
- Specific components in the rock can react with agents like water or acids (from acid rain), which weakens the rock and causes it to crumble.
- After breaking, these are either swept away by forces like wind or air, changed into another element, or consumed by the environment.
- The Rocks’ molecular structure is altered by them.
Read More: Types of Rocks
Chemical Weathering Types
Some of the major chemical weathering processes are Oxidation, Reduction, Solution, Carbonation, and Hydration.
Chemical Weathering Oxidation & Reduction
The mixing of minerals with oxygen to form oxides and hydroxides is called oxidation. Oxidation occurs when there is ready access to oxygenated water in the atmosphere. The oxidation process results in the fragmentation of rocks. The minerals that are affected by oxidation are Manganese, Sulphur, Iron etc.
The oxidised minerals are present in a situation where oxygen is absent, and reduction occurs. Such circumstances are found below the water table and stagnant water. These Weathering processes are interconnected.
Chemical Weathering Dissolution
Earth materials dissolve in acid or water to form a solution of water and the dissolved substance. The materials disintegrate to form a suspension in water after coming in contact with water. The disintegration of the solids depends upon the solubility of minerals in weak acids or water. Some rocks get affected by this process after coming in contact with water or acid rain.
For example, Rock-forming minerals like nitrates, potassium and sulphates dissolve and are leached out thus causing chemical weathering.
Read More: Mass Movement
Chemical Weathering Carbonation
Carbon dioxide is transformed into carbonates, bicarbonates, and carbonic acid through the process of carbonation. Carbonation weathering is the process of atmospheric carbon dioxide-causing solution weathering. Small amounts of atmospheric carbon dioxide are dissolved by rain, creating a weak acid that can dissolve rocks like limestone (calcium carbonate) (solution weathering).
Caves form when subsurface water that contains carbonic acid flows through limestone blocks, dissolves the limestone, and leaves behind empty pockets (caves) (E.g. Karst topography).
As the temperature decreases, the carbonation process quickens because cooler water holds more dissolved carbon dioxide gas. Carbonation is hence an important component.
Chemical Weathering Hydration
The chemical addition of water is called hydration. Minerals enlarge after coming in contact with water. The resulting enlargement increases the volume of the material or rock. The sustained recurrence of this process can lead to fatigue in the rocks. This may lead to the disintegration of rocks.
Chemical Weathering Hydration Diagram
The chemical process of hydrating a mineral involves the firm attachment of H+ and OH- ions to the mineral’s atoms and molecules. Here is an illustration of Hydration Weathering.
Chemical Weathering Hydrolysis
In biological hydrolysis, a water molecule is consumed to influence the division of a larger molecule into constituent parts. In biological hydrolysis, pure water reacts with silicate or carbonate minerals to totally dissolve the starting material (dissolution weathering). Climate change may be impacted by biological hydrolysis, which is a crucial response in controlling CO2 levels in the atmosphere.
Chemical Weathering Hydrolysis Diagram
A water molecule is consumed to influence the division of a larger molecule into constituent parts. Below is the diagrammatic illustration of Hydrolysis.
Chemical Weathering UPSC
The initial stage in the creation of soil is chemical weathering, particularly hydrolysis and oxidation. Chemical weathering happens as a result of the constant and progressive nature of weathering, which over time alters the mineralogy of eroding, cracking, or collapsing stones. Water and oxygen binding via procedures like hydrolysis and oxidation has a significant impact on changes in rock composition. Chemical weathering is crucial for several types of landforms and for the movement of minerals in the soil.
The topic “Chemical Weathering”, which is an important element of the UPSC Exam’s Geography Syllabus, should be thoroughly studied by candidates.