[dystorsion]

Hail my fellow scholars!

I was presented with this question in an assignment. It seems to be of a thinking type:

Use the oxidation number concept, and other considerations, to explain why CO2 makes an effective fire extinguisher.

The answer seems to elude me. Can you helpful people help me out?

Thanks a bunch,
Dystorsion

[Atome]

Good question. I am not entirely sure, but the CO₂ would replace O₂, which is an oxidising agent. Thus, the combustion reaction (a redox reaction) would cease.

Also, C

[Atome]

Good question. Here's my guess: Since CO₂ is denser than air, it would replace O₂, an oxidising agent. Thus, the combustion reaction (a redox reaction) would cease.

Also, carbon dioxide is a covalent compound and has nonpolar bonds, so it would not conduct electricity in the event of an electrical fire.

Lastly, carbon dioxide would leave no harmful residues after the fire has been extinguished.

Please let me know if I am missing something; I don't think that I have fully delved into the oxidation number concept in this reply.

[LQ43]

Atome seems to have covered the "other considerations"

Oxidation numbers are calculated according to the rules:

http://www.chemistry.nmsu.edu/studntres/exercises/ox_rules.html

Using these, calculate the oxidation number for O in O2, then calculate and compare the oxidation number in O in CO2.

Can CO2 be used as an oxidizing agent then?

[Atome]

Thanks for your reply, LQ43.

In O₂, oxygen's oxidation number is 0 as it is in its standard state. In CO₂, oxygen's oxidation would be -2.

Consequently, I believe that CO₂ would not be an oxidising agent because the O₂CO₂ already has the two extra electrons needed to fill its other shell according to the octet rule. Thus, carbon dioxide would generally stop combustion.

Would this answer be correct?

[LQ43]

Yes, in CO₂, the O is already reduced and can't be reduced further (at least under ordinary combustion conditions) unlike its state in O₂.