* New substances are formed: The wax (hydrocarbon) in the candle reacts with oxygen in the air. This chemical reaction produces carbon dioxide, water, and soot (carbon). These are entirely different substances from the original wax and oxygen.
* Irreversible change: Once the candle is burned, you can't simply reverse the process to get back the original wax. You can't easily separate the carbon dioxide, water, and soot to recreate the wax.
* Energy is released: Burning a candle releases energy in the form of heat and light. This is a clear indication that chemical bonds are being broken and new ones are forming.
Contrast with Physical Change:
A physical change alters the form or appearance of a substance but does not change its chemical composition. For example, melting ice is a physical change because the water molecules themselves remain the same, they are just arranged differently.
In summary: The burning of a candle involves a chemical reaction where new substances are formed, the process is irreversible, and energy is released. These are all hallmarks of a chemical change.
