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Topic: Chemical Equation Naming

Posts 21 to 23 of 23

iKhan

baba_944 wrote:

Now for combustion, does it have to be both CO2 and H2O or one or the other?

Both.

Octane wrote:

iKhan wrote:

Octane wrote:

unrandomsam wrote:

I thought combustion could happen with elemental fluorine instead of oxygen.

(I am interested in Chemistry but haven't done any for 12 years).

It is possible. Any reaction with an oxidant is technically a combustion. Actually, all halogens are able to take the role of an oxidant during a combustion. However most combustions occur in the presence of oxygen.

Hmm. Didn't know that. So how can you distinguish combustion from any redox reaction?

Since electrons are transferred during a combustion reaction; they are considered redox reactions as well. Take the example of a combustion reaction I gave earlier:

CH4 + 2 O2 -> CO2 + 2 H2O

Even though it seems difficult to keep track of the electrons during a reaction like this; they are in fact moving around. Use oxidation numbers to keep track of the electrons:

CH4 + 2 O2 -> CO2 + 2 H2O
(-4)(+4) + 2 (0) -> (+4)(-4) + 2 (+2)(-2)

With this knowledge, we can easily identify the half-reactions:

Oxidation reaction: CH4 -> CO2 + 8 e-
Reduction reaction: 2 O2 + 8 e- -> CO2 + 2 H2O

The rule of thumb that is usally given when explaining combustion reactions is that CO2 and H2O are reaction products. Although this is the case in the combustion reaction of methane in oxygen, this doesn't apply to the combustion of methane in, say, fluorine. Fluorine has a high electronegativity, causing it to react instantly with most other elements. Since a combustion is nothing more than a rapid redox reaction, the instant and violent reaction caused by fluorine in the presence of a reducing agent (fuel) will ignite the fuel, just like it would in the presence of oxygen.

Now, fluorine doesn't naturally occur in high concentrations, and since storing it is quite difficult, a combustion reaction with fluorine as the oxidant isn't very common. Therefore, the rule of thumb still applies in the majority of combustion reactions.

I get that combustion is redox. What I don't get is what distinguishes it from any old redox reaction?

Currently Playing: Steamworld Heist, The Legend of Zelda: Majora's Mask, Tales of Graces F

Octane

iKhan wrote:

I get that combustion is redox. What I don't get is what distinguishes it from any old redox reaction?

The reaction products of a combustion reaction contain the element of the oxidizing agent, whereas this is not the case in other redox reactions.

Combustion reaction:

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O (Note that oxygen is the oxidant, and that both end products contain oxygen)

(non-combustion) Redox reaction:

Ag + H2S -> Ag2S + H2 (In this example hydrogen is the oxidant, however it is not present in both reaction products)

Edited on by Octane

Octane

baba_944

Thanks for the help. I understand it now. Also, it's funny how I ask for help for a specific Chem. problem, it goes into a very well discussion for Chem.

Who are you?

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