Answer – Burning wood is a chemical change. When wood is heated in the presence of oxygen, an irreversible reaction occurs, leading to the formation of new substances—carbon dioxide, water vapor, and ash.

Explanation: 

A physical change is temporary and results in a substance’s physical properties, such as shape, size, etc., being altered but not its chemical composition. Such a change does not lead to new products being formed. A chemical change, on the other hand, is permanent as it involves a chemical reaction. It leads to new substances being produced due to the original substance’s physical and chemical properties changing.

When it burns, wood reacts with oxygen in the air. This can be expressed in the form of a chemical reaction with wood being represented by its primary component cellulose:

$$\begin{gathered} {\mathrm{C}}_6{\mathrm{H}}_{10}{\mathrm{O}}_5 \left(\mathrm{s}\right) + 6 {\mathrm{O}}_2 \to 6{\mathrm{CO}}_2 \left(\mathrm{g}\right) + 5 {\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right) \\ \mathrm{Cellulose} \mathrm{Oxygen} \mathrm{Carbon} \mathrm{Water} \\ \mathrm{dioxide} \mathrm{vapor} \end{gathered}$$

Cellulose, which is the original component, undergoes combustion (a reaction with oxygen to generate heat and light) to result in the new products carbon dioxide and water vapor. The burnt wood also leaves behind ash as a byproduct. Since burning wood is a reaction that is hard to reverse and leads to new substances being formed from the original one, it is considered a chemical change.

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