how physical/mechanical and chemical weathering different?
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Physical/mechanical weathering and chemical weathering are two different processes that contribute to the breakdown and alteration of rocks and minerals. Here's an explanation of each process and how they differ:
1. Physical/Mechanical Weathering:
Physical/mechanical weathering involves the physical breakdown of rocks into smaller pieces or fragments without changing their chemical composition. It occurs through various mechanisms, including:
a. Frost Wedging: Water collects in cracks of rocks, then freezes and expands, exerting pressure on the surrounding rock and causing it to crack.
b. Abrasion: The wearing down or breaking of rocks through friction caused by wind, water, or other rocks rubbing against them.
c. Pressure Release: Overlying material is eroded or removed, leading to the expansion and fracturing of rocks beneath due to the release of pressure.
d. Biological Activity: Plant roots, burrowing animals, and other organisms can exert physical stress on rocks, leading to their fragmentation.
In physical/mechanical weathering, the chemical composition of the rocks remains the same. The process primarily breaks down rocks into smaller pieces, increasing their surface area for subsequent weathering processes.
2. Chemical Weathering:
Chemical weathering involves the alteration of rocks and minerals through chemical reactions, leading to the transformation of their composition. It occurs through various chemical processes, including:
a. Hydrolysis: Rocks react with water, leading to the breakdown of minerals and the formation of new minerals.
b. Oxidation: Oxygen in the air reacts with certain minerals, such as iron, resulting in the formation of oxides and rust.
c. Carbonation: Carbon dioxide dissolves in water, forming a weak acid that reacts with rocks containing carbonate minerals, such as limestone, causing them to dissolve.
d. Acid Rain: Rainwater containing acids, formed due to pollution, reacts with rocks and minerals, leading to their dissolution or alteration.
Chemical weathering can change the composition and structure of rocks on a molecular level, making them more susceptible to physical weathering processes. Over time, chemical weathering can lead to the significant alteration and decomposition of rocks.
In summary, physical/mechanical weathering refers to the physical breakdown of rocks without changing their chemical composition, while chemical weathering involves the alteration of rocks through chemical reactions, resulting in changes to their composition. These processes often work together, with chemical weathering weakening rocks, making them more susceptible to physical weathering.