[UCSC14]

Calculate Ksp for iron(II) sulfide given the following data.

FeS(s) + 2 e‾ → Fe(s) + S^2-(aq) E° = −1.01 V

Fe²⁺ (aq) + 2 e‾ → Fe(s) E° = −0.44 V

It starts by flipping the second half reaction. This is my question how do you know which one to flip? For spontaneous you always flip the smallest value but, this one is not spontaneous but I'm not sure how i can tell from the information given. I don't need anyone to solve I just need an explanation on how to know which to flip.

[Borek]

Hard to answer not seeing how it was solved, but - does it matter for the final result which reaction was flipped?

[UCSC14]

Yes, If flip -.44 the answer is 5.14e-20

but if you flip -1.01 it is 1.94e19

[UCSC14]

The problem uses the Nernst equation which I know I just need E°cell

[mjc123]

If flip -.44 the answer is 5.14e-20

That is K for what reaction?

if you flip -1.01 it is 1.94e19

That is K for what reaction?

[Borek]

5.14×10^-20×1.94×10¹⁹ = 1.

No accident here.

Actually it is the same hint mjc gave.

[UCSC14]

I was able to talk to my professor and he said when looking for the Ksp i need to use the form

Solid  Aqueous + Aqueous

This is how I'm supposed to know how to flip it he said.