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| A reductionist approach towards redox |
Here goes...
If there's one thing you must know about how I learn, it's that I do so really slowly. And I'm serious about it! No sarcasm, no hypocrisy.
When I learn something new, I take a long time to process the new information.
And this is significant because the topic I would like to share today is one that I have only just recently had an epiphany on; prior to this Eureka moment, I was confused and lost despite having learnt the topic first back in 2013. And it makes me really happy now to be able to share with you guys what I took so long to realise.
p.s. It may very well turn out that my conclusive revelation is WRONG and perpetually misleading so please don't use the content in this post as a factual guide - I am looking for my post to serve as merely an inspiration or thought-provoker for lost students.
Okay, enough of clarification - time to tackle the subject on hand: Galvanic and Electrolytic Cells.
Let me just dive into the burning question that I had been asking myself for the past few weeks:
Why is the anode negative, and the cathode positive in a Galvanic cell?
I know that some of you out there might be rubbing their eyes to re-read the question above, and possibly passing a judgement of my intelligence level right now: "Wait, did she really just ask such a simple question?" ... But nevertheless I know that there has to be other students who are as lost as I was before I (presumably) came up with a solution.
Now a little background information just to facilitate our understanding:
Galvanic Cells are electrochemical cells that convert chemical potential energy into electrical energy (think of a battery) ... This is driven by a spontaneous redox reaction that occurs between two metals of differing reduction potentials. What this means is that
Electrolytic Cells on the other hand are electrochemical cells that convert electrical energy into chemical energy. This requires an external output of energy (so you could imagine a galvanic cell being connected to an electrolytic cell....somehow)
The main similarity between these two cells is that the electrons ALWAYS flow towards the cathode. So how is it that electrons can flow to positive and negative electrodes?
I choose to look at it from a chronological perspective and determine the sequence of events in the chemical reaction: What leads to what occurring?
In a galvanic cell, it is the difference in reduction potential that drives the flow of electrons. This means that within the two electrodes, the charges have already been assigned. How do we know what charges these are? The electrode with the lower reduction potential will be oxidised, whereas the electrode with the higher reduction potential will be reduced, meaning that electrons will be migrating towards that electrode.
Working backwards, we need to acknowledge that there must have been a certain force that drove the electrons towards that certain electrode instead of the other...
And it is none other that its positivity.
Bear with me for a while! I know there are other issues with this assumption, including the fallacy that a positive electrode cannot attract positive ions because of the similar charge (remember RED CAT, AN OX --> The reduction occurs at the cathode, which should be attracting positive cations) However, this can be explained by once again looking at the sequence of events. In this case, the cathode is positive, leading to the flow of electrons towards it. The cations are attracted to the electrons, therefore flowing towards the cathode. And we also need to bear in mind that the 'positivity' of the cathode is not an actual charge, more like one that is characterised as static charges (I hope I remember my Physics) ... We can imagine the electrons going towards the cathode, and the electrons within the cathode fleeing to the opposite end due to repulsion. The cations are then attracted to the electrons within the cathode....
I feel like I'm writing a bunch of bull-crap here.
But all is well! My blog is after all a mere avenue for me to unleash my thoughts (quite queer that I think about stuff like this during my free time, no?)
Anyway, you could also think of the cathode as a piece of paper that is not participating in the 'attraction' at all, and rather just allowing the electrons to be attracted to the cations and vice versa. Let's just say that the positive ions are attracted to the electrons which are attracted towards the positive electrode. Therefore, positive ions flow to the positive cathode.
Now how this is different from an electrolytic cell is that in the latter, you have an input of electricity that drives the chemical reaction. That means that the direction of flow of electrons are already fixed, and the oncoming traffic of electrons towards the cathode makes it the negative electrode (it is not positive because it did not attract the electrons over. Rather the electrons were 'forced upon' them) ...
And there you have it. My explanation as to why the cathode is positive and the anode is negative in an galvanic cell (I did not address this part but it's simply the polar opposite ... get the pun?)
To be honest, I had expected my explanation to go better than this, but I guess I overestimated myself. Anyhow, I hope I have helped some of you out there! If I have failed to, I sincerely apologise for your wasted time.
Maybe leave a suggestion in the comments below, or if you'd prefer, my Ask.fm to tell me how I can improve on my Nerdalicious series (Yes! I have decided to arrange my posts in series [omg another pun] so as to make my blog more structured and hopefully more interesting - and Nerdalicious is my label for the series of academics-related content)
I wonder what my next post will be about?
xoxo
Valerie
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