* New substances are formed: Natural gas (primarily methane) reacts with oxygen in the air. This chemical reaction produces carbon dioxide, water vapor, and heat. The original substances (methane and oxygen) are transformed into entirely new substances.

* Irreversible: The process of burning is not easily reversed. You can't simply recombine the carbon dioxide and water back into methane and oxygen.

Key characteristics of chemical changes:

* Formation of new substances

* Irreversible or difficult to reverse

* Often involve energy changes (heat released or absorbed)

Let me know if you have any other questions!