What is the definition of chemical weathering?

Answer 1

Weathering is the first step for a number of other geomorphic and biogeochemical process. The products of weathering are the major source of sediments for erosion and deposition.

There are 3 broad categories of mechanisms for weathering:
Chemical
Physical
Biological

Chemical weathering - involves the alteration of the chemical and mineralogical composition of the weathered material.

Answer 2

It could be found easily by looking it up in your textbook glossary or index or lab manual.