braves09

the problem gives you a diagram of two electrodes immersed in a beaker with a wore connecting the electrodes (hopefully you can picture this).
then it gives you two reduction half reactions with E values for them.
the question asks, "on the diagram, indicate the direction of electron flow in the wire."

how would you decide which directions the electrons flow? i thought they went from the anode to cathode, but it doesnt in this problem, the answer says it goes from right to left, and that is the cathose to anode. please help thanks

niubie

electrons should flow from the anode to cathode, so maybe the answer to the problem had a typo?

pyrotix

Apologies if this thing is unnecessary:

High E values show tendency to be reduced (Fluorine). Low E values show tendency to be oxidized (Lithium).

The half reaction (if they are both forward) that is more negative is the one that will occur (in reverse) at the anode. Electrons will flow from the one you just selected to the opposite electrode which would be the cathode.

If that doesn't work note are you really asked to find direction of current or electron flow? Cause current goes cathode to anode for some braindead historical reason I believe...

It is also possible if it is from one of those cram books that a question was marked down wrong.

chaz90

Anode=oxidized
Cathode=reduced

PrescitedEntity

There's some buggery when electrolytic cells are involved, isn't there?

sushant269

no electrons flow opposite of something lol. I dont remember that something.

chaz90

Holy crap at that triple post at the same time.

tpaschoal

e-s definately flow from the anode to the cathode...thats where reduction occurs so they go there to help out with the reduction after they are kicked out in the oxidation.

sushant269

i know, i was wondering why mine is all the way down there!

PrescitedEntity

Wow.

And sorry, my bad. Electron flow is still anode to cathode; positivity is what changes.

Yeah, there's some weird thing about naming one or the other anode/cathode.

I'd say go with anode to cathode, though, since CB will probably use that.

chaz90

Make sure you calculated which is cathode and which is anode correctly.

awf7285

Hey a further thing on this question. For electrochemical cells, how do you know which of the metals, say Cu and Ag, will be the anode and which will be the cathode if you don't have the overall or half-cell reactions?? I'm stuck!

(I know that the overall reaction turns out to be Cu(g) + 2Ag+(aq) -> 2Ag(s) + Cu2+(aq). But why that way? Why not the other way round? )

THANKS.

PrescitedEntity

Reduction potential. The one with the higher reduction potential is oxidized, and therefore, the anode.

chaz90

It's all about the oxidation numbers you calculate.

PrescitedEntity

I guess that'd work too, if you're given the equation.