Question

spontaneous and nonspontaneous question
Sorry, it's been so long since i've done these need a little refreshing.
A redox reaction occurs between aluminum and chromium with the half-reactions shown. What can you conclude about the spontaneity of the reaction?

Answer 1

@praxer hoping you can help me on this one too

Answer 2

I think it's either B or C but I might have the equation the opposite way

Answer 3

Okay, here I would like to introduce you to a formula involving gibbs free energy, nF which is the amount of charge passed.

according to the law

$$\triangle _rG^0=-nFE^0_{(cell)}$$

now, here n means number of electrons involved and F is the faraday's constant= 964857 C/mol)

for the equation if we set up it will be $$Al^3++Cr \rightarrow Cr^3++Al$$
hence the E^0 cell = -1.66+0.92=-0.92

hence, find the gibbs free energy. If it is less than zero than it is spontaneous or it non spontaneous.

If you need the derivation of the formula above tell me I will provide you.

Answer 4

Provided here n will be 3 as 3no.s of electrons are involved.

Answer 5

is the -0.92 the number of electrons? I'm a little lost on where that came from. @praxer

Answer 6

i get the E^0 cell and the equation but what does it have to do with the delta G equation?

Answer 7

yes the E cell is 0.92 so gibbs free energy is $$-3*96487*-0.92$$= some positive number hence the option B . Hence the process as non spontaneous. as the gibbs energy is +ve.
This question is involving concepts of gibbs free energy and electrochemistry I will provide you the details of gibbs free energy and the formula.


OPTION B IS CORRECT.

Answer 8

Gibbs free energy give us the spontaneity and non spontaneity

Answer 9

Did you understand it. If you are having any problem than do say, we will try to sort it out. :)

Answer 10

ohhh got it! thank you so much! I was a little confused but you cleared that up thank you so much!

Answer 11

This is the what the use of GIBBS energy is.

Answer 12

yeah i went online and found that too :) thank you!

Answer 13

Thank you for letting me to serve you. Keep using OS. :)