Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: LucaZombini on February 10, 2021, 06:25:36 PM
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determinate the direction of the reaction 2Fe3+ + 2I- ::equil:: I2 + 2Fe2+ when every specie is 1 mol/dm-3 and find the concentration of every ionic specie when the equilibrium is reached. T = 25 °C
EFe3+/Fe2+ = 0,771V
EI2/I- = 0,536V
given the Nernst's formula i find the Keq
E = RT/zF * logKeq
Keq = 10(zE/0,05916) = 8,8*107
[Fe3+] = [I-] = 1-2x
[Fe2+] = 1+2x
then i don't know how to proceed. i've tried to substitute the results above in the Keq equation but i wasn't able to find the results.
for example
Keq = 1+2x/(1-2x)2
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What is the expression for Keq for the reaction
2Fe3+ + 2I- ::equil:: I2 + 2Fe2+ ?
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Keq = [Fe2+]2 [I2]/ [Fe3+ ]2 [I-]2
I2 should be solid, i think.
EDIT:
I forgot to write the solutions
Fe3+ = I- = 1,44E-2
Fe2+ = 2-1,44E-2
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Yes (leaving out [I2] which is a solid). That is not (1+2x)/(1-2x)2, is it?
You could simplify it by writing
Fe3+ + I- ::equil:: 1/2 I2 + Fe2+
for which z = 1 in the Nernst equation. Then
Keq = [Fe2+]/[Fe3+][I-]
but this Keq has a different value from the one you calculated.
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I've managed to solve it by making an approximation which eliminated some terms!! :)
i counted z as 2, that's how i found that value for Keq