* Physical change: A change in the form or appearance of a substance but not its chemical composition. Examples include melting ice, cutting paper, or dissolving sugar in water.

* Chemical change: A change that results in the formation of new substances with different chemical compositions. Examples include burning wood, rusting iron, or cooking an egg.

Why manure formation is a chemical change:

* Decomposition: The leaves undergo decomposition by microorganisms, breaking down the complex organic molecules into simpler substances.

* New substances: The process creates new substances like humus, a rich organic matter that enriches the soil. This is a change in chemical composition.

* Irreversible: The process is irreversible; you cannot easily turn manure back into leaves.

Therefore, the formation of manure from leaves involves a breakdown of the original chemical structure and the creation of new substances, making it a chemical change.