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How would I find the half-reactions?

by Bipolarity
Tags: halfreactions
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Bipolarity
#1
Feb19-12, 09:27 PM
P: 783
[tex]2MoS_{2} + 7O_{2} \rightarrow 2MoO_{3} + 4SO_{2} [/tex]

So here I have a redox reaction, it's already balanced but just for kicks I'm trying to find the half-reactions so that I know what is happening. I'm having some trouble though as I don't know what's being oxidized and what's being reduced. Any advice?

Thanks!

BiP
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Borek
#2
Feb20-12, 01:44 AM
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P: 23,588
Two things are oxidized and one is being reduced.

The one that is being reduced should be obvious.
Bipolarity
#3
Feb20-12, 07:02 PM
P: 783
Sorry I don't catch it still. Which one is being oxidized and how do you know?

BiP

moouers
#4
Feb20-12, 11:50 PM
P: 81
How would I find the half-reactions?

Did you try assigning oxidation numbers?

If you're not sure about how to do that, this should help:
http://chemistry.about.com/od/genera...xidationno.htm

Also, khanacademy.org has some excellent videos (I think three in total) about redox reactions and oxidation states. Start with this one: http://www.khanacademy.org/video/int...opic=chemistry and work your way through the next few.

I also recently asked a question about balancing by half-reaction method here, and got some good help which may in turn help you: http://www.physicsforums.com/showthread.php?t=578120
Bipolarity
#5
Feb21-12, 10:46 AM
P: 783
The problem is both Molybdenum and Sulphur have variable oxidation numbers so I don't know what they are.

BiP
Borek
#6
Feb21-12, 01:24 PM
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Polysulfides are a little bit tricky. In general they have a form Sn2-. For S22- you can safely assume both sulfur atoms are identical and each has an oxidation number of -1. This is analogous to hydrogen peroxide where both oxygen atoms are assigned ON of -1.


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