Question

Explain why the burning of wood and cutting it into small pieces are considered as two different types of changes.

Answer 1

Hint: Try to recall that in a physical change, no new substances are formed whereas in a chemical change, bonds are broken and new substances are formed. Now, by using this you can easily answer the given question.

Complete step by step solution:
-It is known to you that in a physical change, no new substance is formed and it is a temporary change (it can be reversed) except in some cases. The substance interacting with another will retain their characteristics.
-Physical changes cause a change in shape and size or phase and these changes are reversible. In a chemical change, a new substance is formed and is a permanent change.
-The substance involved changes their identity in a chemical change.
-The mass of substance does alter in a chemical change and also, a lot of heat energy or light is given out or absorbed.
-Chemical changes affect both chemical and physical properties and are irreversible.
-Now, coming to the question, burning wood is a chemical change because new substances (carbon dioxide and ash) are formed and cannot be changed back. A lot of energy in the form of light is given out. This is a combustion reaction and the components of the wood are oxidized.
-Whereas in cutting of wood no new substance is formed and the original properties of the substance, here wood, are intact. So, this is a physical change.

Note: In a chemical change, the bonds of the molecules that make up the material may change in nature i.e. may be broken or created. Here, when the wood is burned, the evolution of a gaseous substance does take place, but this cannot be called a mere phase change since the constituent molecules of wood have to be broken down to form carbon dioxide (evolved during combustion). Carbon dioxide is not present in the wood in the solid-state.