entropy a2 ocr feasibility and free energy

hi
can someone confirm my understanding is correct?
when free energy delta G is less than 0 the reaction is feasible
and spontanenous (whats the difference) for exothermic reactions
for endothermic reactions delta S must be positive and the temperature is high enough so temp* delta S is more negative/greater than delta H??

also with electrode potentials -its feasible when the answer is a positive voltage- i think thisis where i got abit confused



thank you so much! pos rep

hi
can someone confirm my understanding is correct?
when free energy delta G is less than 0 the reaction is feasible
and spontanenous (whats the difference) for exothermic reactions
for endothermic reactions delta S must be positive and the temperature is high enough so temp* delta S is more negative/greater than delta H??

also with electrode potentials -its feasible when the answer is a positive voltage- i think thisis where i got abit confused



thank you so much! pos rep

The difference between feasible and spontaneous is how easily it is done. A feasible reaction is a reaction which is thermodynamically possible, but might not happen at a given temperature, while a spontaneous reaction is a reaction which will just happen of its own accord at that temperature.
And yes, when G<0 a reaction is feasible.

Electrode potentials which are greater than +0.6V will happen. Below 0 they are impossible. Inbetween i'm a bit fuzzy on, i think they can happen under certain circumstances but are unlikely to.

Enthalpy deals with whether a reaction is spontaneous. If deltaS total is positive it is spontaneous. [DeltaS]

For the second to last line: deltaG = DeltaH - T(DeltaS system), so you want T*DeltaS of system to exceed Delta H. In other words, you want T*DeltaS to be a bigger positive number than DeltaH

Hope this helps!

Edit: FSM damn it, double sniped!

Sorry, that isn't strictly true.... A reaction is spontaneous if it satisfies DeltaGr (gibbs free energy) < 0, not enthalpy.

Edexcel A2 Chemistry, page 42:

'It is the total entropy change which determines whether this reaction is spontaneous or not'

It follows on page 45:

' Since DeltaS must be positive for a change to occur spontaneously, it follows that such changes have DeltaG less than zero'

Seems like there you can take from both, none taking priority

Edexcel A2 Chemistry, page 42:

'It is the total entropy change which determines whether this reaction is spontaneous or not'

It follows on page 45:

' Since DeltaS must be positive for a change to occur spontaneously, it follows that such changes have DeltaG less than zero'

Seems like there you can take from both, none taking priority

That must be out of context as that is just wrong.... Sorry but university level chemistry is more reliable than exam board specifications.

Considering the amount of lies i discovered were told to me in gsce, i'll buy that :L But i tried to keep it as in context as possible

Entropy does not make a reaction spontaneous. It is Gibbs free energy for systems at constant pressure, or Helmholtz free energy at constant volume.
Entropy is just a constituent term for both of these free energies.
The physical requirement of entropy is that for any process the entropy of the universe must increase. This applies to both spontaneous and non-spontaneous reactions.

I can run you through a bit of thermodynamics quickly if you would like? It really is not covered well at A-level so you don't get a real idea of what the functions actually are.

I'm doing entropy for my Unit four exam / I've got some good notes - if you want them?
By the way how can you send images via I phone ? (I'm new on here!)

thank you! yes please!
I can PM you my email?
To upload it on here, the box you type in with the reply has a little row above it with font, colour, bold and one of the icons is an image and you can upload via that.

It won't let me - upload the images ������- when I click the icon and upload image it remains blank ?

I know that 0.3V is the actual value at which an EC cell will go to completion, but at a-level, or in OCR A at least, I've been taught, and it says, that it's 0.4V

What do you mean by go to completion? This never came up when I did A-level and doesn't make sense from the point of view of thermodynamics.