* Decomposition: Rotting is caused by bacteria and fungi breaking down the complex molecules in the tomato (sugars, proteins, etc.) into simpler substances. This involves chemical reactions that alter the composition of the tomato.

* New Substances: The rotting process produces new substances like acids, gases (like methane), and alcohols, giving the tomato a distinct smell and mushy texture.

* Irreversible: Unlike a physical change (like freezing or melting), the chemical changes involved in rotting are irreversible. You can't easily "unrot" a tomato.

In summary: Rotting involves breaking down the original tomato molecules into new substances, indicating a chemical change.