Cause-Biological weathering is weathering caused by plants and animals. Plants and animals release acid-forming chemicals that cause weathering and also contribute to the breaking down of rocks and landforms.
Effects-Some of the effects of biological weathering are the breaking of particles, movement of minerals, mixing of materials and production of carbon dioxide.

Chemical weathering is caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic.Chemical weathering changes the molecular structure of rocks and soil. For instance, carbon dioxide from the air or soil sometimes combines with water in a process called carbonation. This produces a weak acid, called carbonic acid, that can dissolve rock.

These chemical processes need water, and occur more rapidly at higher temperature, so warm, damp climates are best. Chemical weathering (especially hydrolysis and oxidation) is the first stage in the production of soils.

       Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind or water. A similar process, weathering, breaks down or dissolves rock, but does not involve movement.

Differences  of erosion and weathering 

So, if a rock is changed or broken but stays where it is, it is called weathering. If the pieces of weathered rock are moved away, it is called erosion.

             Chemical erosion

Chemical erosion involves weathering done by interactions between chemicals in water (usually a dilute form of acid, as in acid rain) and in rocks or sediments, especially carbonate sediments like limestone that dissolve in acid.