* Burning wood: The wood reacts with oxygen in the air, producing ash, smoke, and heat. The original wood is gone, transformed into new substances.

* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust). This is a slow process, but the iron changes its composition and properties.

* Baking a cake: The ingredients mix and react chemically, resulting in a completely new substance with different properties.

* Digesting food: Enzymes in your body break down the food into smaller molecules, changing its composition.

* Photosynthesis: Plants use sunlight, water, and carbon dioxide to create glucose and oxygen. This is a fundamental chemical change vital for life.

Key characteristics of chemical changes:

* Formation of new substances: The original substances are transformed into different substances with different properties.

* Difficult or impossible to reverse: While some chemical changes can be reversed (like cooking an egg), many are permanent.

* Energy is often released or absorbed: This can be in the form of heat (burning wood), light (photosynthesis), or other forms of energy.