Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Araconan on September 06, 2012, 08:00:56 PM
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Hello,
So I'm currently attempting problems where I have to rank elements/compounds based upon how well they function as either an oxidizing agent or a reducing agent. When ordering compounds in terms of increasing strength as an oxidizing agent, I just ranked them in terms of increasing reduction potentials. When ordering compounds in terms of increasing strength as an reducing agent, I just took the negative of the same reduction potentials I used before, and then ranked them in increasing value. However, what I noticed was that my textbook were using different values when ordering the compounds for increasing strength as a reducing agent. It took the reduction potentials where the reaction had the compound on the right side without having to reverse the reaction, and the reduction potentials also had different values.
Ex. 2H2O + 2e :rarrow: H2 +2OH- -0.83V (I used this value when ordering in terms of increasing strength of oxidizing agent)
When then ordering compounds in terms of increasing strength in reducing agent, I just reversed the above equation, and used 0.83V.
However, my textbook used O2 + 4H+ + 4e :rarrow: 2H2O 1.23V.
What I'm wondering, is why can't I used 0.83V? Whenever I combine two half reactions together, I'm always reversing the value for one of the reduction potentials, so why is it wrong to reverse the reduction potential of the equation here?
Thanks in advance!
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When then ordering compounds in terms of increasing strength in reducing agent, I just reversed the above equation, and used 0.83V.
You can't just change sign. Both reduction and oxidation go at exactly the same potential. We list them in tables as reduction potentials for consistency.