Is combustion a physical or chemical change? Why?

1 Answer
Simon Moore
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_2O(s)# and after is #H_2O(l)#. 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(s) + O_2(g)#, and end up with carbon dioxide #CO_2(g)# 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!)

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