# Is combustion a physical or chemical change? Why?

Mar 27, 2017

Chemical.

#### Explanation:

Look at the chemical make-up of the substances after the change, and compare them with the chemical make-up before the change. Is it different?

When ice melts, the chemical makeup before is ${H}_{2} O \left(s\right)$ and after is ${H}_{2} O \left(l\right)$. The physical state has changed, but the chemical make-up is the same. Thats a physical change.

Combustion, however.....start with carbon, and oxygen $C \left(s\right) + {O}_{2} \left(g\right)$, and end up with carbon dioxide $C {O}_{2} \left(g\right)$ a completely different molecule - that's a chemical change.

(Don't get sucked into the "physical changes are reversible, chemical changes aren't" nonsense....you'll eventually regret it if you do!)