Chemical weathering occurs as minerals in rocks are chemically altered, and subsequently decompose and decay. Increasing precipitation (rain) speeds up the chemical weathering of minerals in rocks, as seen on tombstones and monuments made of limestone and marble. In fact, water is an essential factor of chemical weathering. Increasing temperature also accelerates the chemical reaction that causes minerals to degrade. This is why humid, tropical climates have highly weathered landforms, soils, and buildings.
Carbonation and Solution: this weathering process occurs when precipitation (H20) combines with carbon dioxide (CO2) to form carbonic acid (H2CO3). When carbonic acid comes in contact with rocks that contain lime, soda, and potash, the minerals calcium, magenesium and potassium in these rocks chemically change into carbonates and dissolve in rain water.
Hydrolysis: this chemical weathering process occurs when water (H20), usually in the form of precipitation, disrupts the chemical composition and size of a mineral and creates less stable minerals, thus less stable rocks, that weather more readily.
Oxidation: this process occurs when oxygen combines with compound elements in rocks to form oxides. When an object is chemically altered in this manner it is weakened and appears as "oxidized”. A good example of this is a "rusting" sign post . The iron in the metal post is oxidizing. Increased temperatures and the presence of precipitation will accelerate the oxidation process.