Chemical vs. Physical Changes: Why Burning Wood Is Chemical

Burning wood is a chemical change because it irreversibly transforms cellulose and lignin into new substances: carbon dioxide, water vapor, ash (calcium carbonate, potassium carbonate), and numerous organic compounds (creosote, polycyclic aromatics). The original wood cannot be recovered.

In contrast, physical changes (e.g., cutting, freezing, dissolving) alter form or state without changing chemical identity. Key discriminators:

• New substance formation (color change, gas evolution, precipitate, heat/light emission)
• Irreversibility under normal conditions
• Energy change (exothermic/endothermic)

Thus, combustion exemplifies a chemical reaction; sawing wood is physical.