Mercury Battery Reaction: Determining the Oxidation Half Reaction

[Math Is Hard]

Howdy. I'm looking at a mercury battery reaction which goes like so:

HgO(l) + Zn(s) --> ZnO(s) + Hg(l)

I need to figure out the oxidation half reaction. What I can tell so far is that Zn is oxidized, since on the reactant side it has a charge of zero, and on the product side, Zn has an individual charge of 2+ in the ZnO compound. It must be losing electrons.

I believe the oxidation half reaction should have Zn on the reactant side and ZnO and some electrons (two?) on the product side, but I can't figure out how to work in the oxygen for the reactant side. Sorry, I'm totally new at this. And I kinda suck at it besides.

Any help is appreciated. Thanks in advance!

 

[Astronuc]

HgO(l) + Zn(s) --> ZnO(s) + Hg(l)

So one has

Hg²⁺ + Zn(s) --> Zn²⁺ + Hg(l)

and the oxygen does not change valence, it is simply transferred form Hg to Zn.

Half cell reactions

Hg²⁺ + 2 e^- --> + Hg

Zn --> Zn²⁺ + 2 e^-

 

[Math Is Hard]

Thanks, Astronuc. So when I write these half reactions, I shouldn't show the oxygen anywhere? I should only show the element that is getting oxidized or reduced? Sorry, I am still struggling with the concept of what I'm trying to represent.

 

[Astronuc]

So when I write these half reactions, I shouldn't show the oxygen anywhere? I should only show the element that is getting oxidized or reduced?

Yeah, that's pretty much what one does. One just writes the oxidation and reduction reactions.

Sorry, I am still struggling with the concept of what I'm trying to represent.

No problem, it took me awhile to get used to the conventions with respect to cathode/anode reactions.

Here is a nice little tutorial - http://www.science.uwaterloo.ca/~cchieh/cact/c123/halfcell.html

This might help too.

Spontaneity of REDOX Systems - http://members.aol.com/logan20/elecspon.html

http://www.life.uiuc.edu/crofts/bioph354/redox.html

 

[Math Is Hard]

Thanks - I really appreciate the help. And the links are great! Hopefully, I'll be able to finish up my homework now.