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Balancing reactions with multiple oxidation state changes?
Posted: Fri Oct 07, 2016 2:41 am
by wutbat
I have learned to balance equations that have 2 or 3 changes in oxidation states, like:
Code: Select all
Zn + HNO3 = Zn(NO3)2 + NH4NO3
However I can't do this with equations like the one below that have more than 3 changes:
I know it can be balanced easily with other methods but, I want to learn this method completely, so... .
Could you explain this
using Oxidation states?
Thank you all.
Posted: Thu Oct 13, 2016 8:44 pm
by expert
Try to split it into two parallel reactions and then combine them back into one
CH4 + O2 = C2H2 + CO + H2
__________________________
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
Posted: Sat Oct 15, 2016 10:08 am
by wutbat
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?
Posted: Sat Oct 15, 2016 10:40 am
by expert
To identify parallel reactions follow elements that change oxidation state to different levels. For example, in this case
CH
4 + O
2 = C
2H
2 + CO + H
2
C
4- ==> C
2- (for CO)
C
4- ==> C- (for C
2H
2)
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/ar ... 6106000496
NH
3 + O
2 ==> NO + NO
2 + H
2O
Two distinct processes can be identified:
NH
3 + O
2 ==> NO + H
2O
NH
3 + O
2 ==> NO
2 + H
2O
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 + H
2O
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
Posted: Sat Oct 15, 2016 12:34 pm
by wutbat
That was awesome! Really enjoyed it, thank you a lot expert.
Posted: Mon Aug 21, 2017 5:28 am
by spadanco
expert wrote:To identify parallel reactions follow elements that change oxidation state to different levels. For example, in this case
CH
4 + O
2 = C
2H
2 + CO + H
2
C
4- ==> C
2- (for CO)
C
4- ==> C- (for C
2H
2)
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/ar ... 6106000496
NH
3 + O
2 ==> NO + NO
2 + H
2O
Two distinct processes can be identified:
NH
3 + O
2 ==> NO + H
2O
NH
3 + O
2 ==> NO
2 + H
2O
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 + H
2O
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