Burning of wood is a chemical change. Reasons are giving below:
(i) New substance ash is formed which is irreversible to wood.
(ii) Heat is produced when it burns.
(iii) Light is produced when it burns.
(iv) Smoke or gas is produced when it burns.
(v) Sound is also produced when it burns.
Cutting it into small pieces is a physical change. Reasons are giving below:
(i) Small pieces are pieces of wood also.
(ii) Size of wood changed. It becomes small.
(iii) Shape of wood changed. Any shape can be get from the log.
Hence, burning of wood and cutting it into small pieces are considered as two different types of changes.