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# Mod 5 (A2) - Difference between feasibility and spontaneity?

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1. I know that if dG is less than 0 then a reaction is feasible, and if the Ecell is positive then a reaction is spontaneous, but is there a link between these two things? And actually, what is the difference between a reaction being feasible and a reaction being spontaneous?

Thanks!
2. Feasible: thermodynamically possible

Spontaneous: can happen without any energy input.

Obviously If something is spontaneous it is also feasible.
3. A reaction may be feasible, but it might not be spontaneous cause it needs an energy input - ie could have a high activation energy.
4. How does E(cell) values relate to feasibility / spontaneity?
5. E(cell) is positive for a feasible reaction, but again, if it has a high activation energy (or maybe another reason which I don't think we need to know).. it doesn't mean it will be spontaneous.

And tbh, the only high activation reaction I've come across so far is the formation of MgO, cause burning Mg needs a high activation energy.

And if that's right, I was just thinking.. is it cause Mg need higher temperatures than standard conditions on 298k? If it is, isn't it that higher tempratures doesn't affect the activation energy? - or is it just the number of particles greater than it?

Meh, I hope I'm not talking rubbish
6. (Original post by ABF)
How does E(cell) values relate to feasibility / spontaneity?
Well we can relate ΔG to Ecell:

ΔG = - nFE, where F is the faraday constant and n is the number of electrons

if E > 0 <=> ΔG < 0

(this is not A-level by the way)
7. (Original post by EierVonSatan)
Well we can relate ΔG to Ecell:

ΔG = - nFE, where F is the faraday constant and n is the number of electrons

if E > 0 <=> ΔG < 0

(this is not A-level by the way)
But we dont need this for A2 right?
8. (Original post by EierVonSatan)
Well we can relate ΔG to Ecell:

ΔG = - nFE, where F is the faraday constant and n is the number of electrons

if E > 0 <=> ΔG < 0

(this is not A-level by the way)
(Original post by irfy)
But we dont need this for A2 right?
9. So if you have two sides of a electrode system together, and you work out the E value, and it's positive, the reaction will happen, and if its negative, nothing will happen?
10. (Original post by ABF)
So if you have two sides of a electrode system together, and you work out the E value, and it's positive, the reaction will happen, and if its negative, nothing will happen?
Yup
11. The LORA rule makes more sense now.
12. (Original post by ABF)
The LORA rule makes more sense now.
Tell LORA I love her....

The words spontaneous and feasible are used interchangeably in several boards. Both are used to mean thermodynamically possible.
Feasible means that there are no theoretical objections to the reaction postulated.
Spontaneous means that the thermodynamics of the proposed process offer no obstacle.

A reaction may be spontaneous (and feasible) although the kinetics make it too slow for practical purposes.

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