GreenD - 30-3-2011 at 15:54
I understand electrochemistry basically, however it doesn't make too much sense to me the annotations they use, hence my confusion when I see
A + B -> C (-1.2 V)
F + H -> K (+3.4V)
So looking at those two equations, what am I suppose to get out of them?
With enthalpy and entropy it was easy - a negative enhtalpy gives off heat, while as a positive entropy is more... 'chaos', and preferred for a
reaction to take place.
However, it doesn't seem to be that way with electrochemistry. I know they are referencing these values against a standard, but what does the value
really tell you? Are large values mean that the reaction is favored? What if they are negative and large? Etc...
Help?
theflickkk - 31-3-2011 at 06:34
In electrochemistry, to determine if a reaction is feasible, the Ecell value has to be positive.
The Ecell value is calculated as:
Ecell = Ered + Eox
The standard electrode potential of a half cell is its electrode potential under standard conditions relative to a standard hydrogen electrode.
From the table of standard electrode potentials, the forward reactions are the reduction potentials. The higher (more positive) the reduction
potential, the more likely it is to be reduced.
Hence from the equations you gave, the reaction
F + H --> K (+3.4V)
will be the reduction reaction.
In order for a reduction reaction to happen, an oxidation reaction has to occur simultaneously. As such, the second reaction will be an oxidation
reaction (opposite of reduction) whereby:
C --> A + B (+1.2V)
Hence to calculate Ecell,
Ered + Eox = 3.4V + 1.2V = 4.6V
Since the Ecell value is positive, it indicates that the reaction is feasible (with regard purely to Ecell that is)
Hope this is of help (:
GreenD - 31-3-2011 at 07:56
So, if you want a reaction to go to completion, you would like a cell with [F] + [H] and your, I guess it would be cathode cell would have [C]....
correct?
I'm asking this because I'm trying to slowly understand the entire deal with electrolysis of water...
Know any good sources to learn about the electrolysis of water form the ground up? I understand the physics of it a lot better than the chemistry, but
still am in the dark about why hydrolysis only needs 1.3v (rather than my presumption of at least ~20v).
Eventually I think we will all have to move to storing energy locally - i.e. making your own hydrogen + oxygen from the sun, or in batteries. Both
require electricity, and I'd like to know as much about it as I can 