The rotting of wood is a chemical change. A chemical change or reaction is when the substance has been altered chemically and displays differences in both chemical and physical properties.
A chemical changes include burning, rotting, cooking or rusting. After a chemical change has occurred, the substance presents a new chemical makeover. There are many signs of a chemical change or reaction, such as the formation of gas bubbles, the appearance of cloudiness, a change in color or the release of an odor. Though the signs are accurate, the only way to completely know if a change is chemical or physical is to perform chemical analyses on the substance.