Writing balanced half reactions

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ckilkeary 2G
Posts: 68
Joined: Fri Aug 09, 2019 12:16 am

Writing balanced half reactions

Postby ckilkeary 2G » Sat Mar 14, 2020 11:12 am

For problem 6L 9. in the chemistry textbook (particularly part a), it wants you to write the balanced half reactions for the redox reaction of an acidified solution of potassium permanganate and iron (II) chloride.

I understand how in the half reactions we get Fe 2+ and MnO4 - because those are the charges we conclude from the molecules we were given, but how do we decide the other ions in the half reaction?
Like how do we know that in one half reaction it should be Fe 2+ ---> Fe 3+ + e- instead of say Fe 2+ + e- ----> Fe + ?

Jacob Motawakel
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Joined: Wed Sep 18, 2019 12:20 am
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Re: Writing balanced half reactions

Postby Jacob Motawakel » Sat Mar 14, 2020 11:47 am

It depends whether the half-reaction is oxidized or reduced. In oxidized half-reaction, the electrons will be on the right side of the reaction because of the loss of electrons. In reduced half-reaction, the electrons will be on the left side of the reaction because of the gain of electrons.

Jessica Chen 2C
Posts: 103
Joined: Thu Jul 11, 2019 12:17 am

Re: Writing balanced half reactions

Postby Jessica Chen 2C » Sat Mar 14, 2020 12:07 pm

We can also look at the reduction potential values for each half reaction to determine which side the electrons should be on for each half reaction. We want Ecell to be positive (in order to be spontaneous) so the more positive reduction potential is the reduction half reaction (with electrons on the left), and the less positive reduction potential is the oxidation half reaction (with electrons on the right).


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