Balancing reactions with multiple oxidation state changes?
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wutbat
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Balancing reactions with multiple oxidation state changes?


I have learned to balance equations that have 2 or 3 changes in oxidation states, like:
Zn + HNO3 = Zn(NO3)2 + NH4NO3

However I can't do this with equations like the one below that have more than 3 changes:
CH4 + O2 = C2H2 + CO + H2
I know it can be balanced easily with other methods but, I want to learn this method completely, so... .

Could you explain this CH4 + O2 = C2H2 + CO + H2 using Oxidation states?
Thank you all.
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Try to split it into two parallel reactions and then combine them back into one

CH4 + O2 = C2H2 + CO + H2
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CH4 + O2 = CO + H2
CH4 = C2H2 + H2

In reality these are two separate processes, and they can occur in different ratios, depends on conditions: temperature, catalyst, etc.

For example, on every 10 first reactions only one second reaction occur. For simplicity (for school task) combine them with the lowest numbers.
Please try by yourself and give us the answer
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wutbat
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Thanks, I got it!
I balanced the two reactions and the sum of them balanced the first equation. 4 1 2 1 7
Another question came to my mind; How can I find out the way to divide the equation?
Should I know the reactions or is there another way to do it?
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To identify parallel reactions follow elements that change oxidation state to different levels. For example, in this case
CH4 + O2 = C2H2 + CO + H2

C4- ==> C2- (for CO)
C4- ==> C- (for C2H2)

these are to independent processes of oxidation of the same molecule: methane

For example, in this real case vanadium-catalyzed oxidation of ammonia http://www.sciencedirect.com/science/article/pii/S0920586106000496

NH3 + O2 ==> NO + NO2 + H2O
Two distinct processes can be identified:

NH3 + O2 ==> NO + H2O
NH3 + O2 ==> NO2 + H2O

You can easily balance each and them mix them in any ratio

In general case look for changes of the same element into different compounds and analyze for a possibility of mixed reaction. Here is a simple example
NaOH + KOH + HCl ==> NaCl + KCl + H2O
in this particular case Cl- plays role in both independent reactions

Here is another example (read GrahamKemp's answer)
http://chemicalforum.webqc.org/viewtopic.php?t=19314
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wutbat
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That was awesome! Really enjoyed it, thank you a lot expert.
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spadanco
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expert wrote:
To identify parallel reactions follow elements that change oxidation state to different levels. For example, in this case
CH4 + O2 = C2H2 + CO + H2

C4- ==> C2- (for CO)
C4- ==> C- (for C2H2)

these are to independent processes of oxidation of the same molecule: methane

For example, in this real case vanadium-catalyzed oxidation of ammonia http://www.sciencedirect.com/science/article/pii/S0920586106000496

NH3 + O2 ==> NO + NO2 + H2O
Two distinct processes can be identified:

NH3 + O2 ==> NO + H2O
NH3 + O2 ==> NO2 + H2O

You can easily balance each and them mix them in any ratio

In general case look for changes of the same element into different compounds and analyze for a possibility of mixed reaction. Here is a simple example
NaOH + KOH + HCl ==> NaCl + KCl + H2O
in this particular case Cl- plays role in both independent reactions

Here is another example (read GrahamKemp's answer)
http://chemicalforum.webqc.org/viewtopic.php?t=19314

The post has good info
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