Electrolysis reactions

[lovingit]

Can someone please explain to me all the steps in predicting electrolysis reactions
-how to predict what will occur at the cathode and anode
thanks in advance

[Martoman]

Yep.

List all the species present.

Then on your electrochemical series locate them. On the left hand side pick the highest up. On the right hand side the lowest. The left side will reduce, that is move to the right, the right will go to the left, that is, oxidise.

[crayolé]

Just to hijack this thread for a bit

Can spontaneous reactions still occur in non-spontaneous conditions/electrolytic cells?

[Studyinghard]

Just to hijack this thread for a bit

Can spontaneous reactions still occur in non-spontaneous conditions/electrolytic cells?

Yes
However it is not called a galvanic cell. If there is a spontaneous reaction and a power supply is connected it is still known as an electrolytic cell. The power supply is just present to quicken the reaction.

[Martoman]

Just to hijack this thread for a bit

Can spontaneous reactions still occur in non-spontaneous conditions/electrolytic cells?

What exactly do you mean? Of course they can! Putting something into the system which will spontaneously react will spontaneously react (at standard conditions).

[scocliffe09]

Just to hijack this thread for a bit

Can spontaneous reactions still occur in non-spontaneous conditions/electrolytic cells?

Just be careful because in electrolysis sometimes spontaneous reactions which may otherwise have occurred can be prevented by putting current through a cell.
e.g. if Cu is the electrode at the cathode in an electrolytic cell, it cannot act as a reductant and be oxidised to Cu2+ as electrons are constantly being thrown at it...

[crayolé]

Just to hijack this thread for a bit

Can spontaneous reactions still occur in non-spontaneous conditions/electrolytic cells?

Just be careful because in electrolysis sometimes spontaneous reactions which may otherwise have occurred can be prevented by putting current through a cell.
e.g. if Cu is the electrode at the cathode in an electrolytic cell, it cannot act as a reductant and be oxidised to Cu2+ as electrons are constantly being thrown at it...

Yeah what Sco said is where I'm getting confused. How do we know what spontaneous reactions wont occur? Whats stopping the products of electrolytic reactions from spontaneously reacting back

[Martoman]

usually a porus barrier blocks this, otherwise its VCE chemistry, you don't ask deep meaningful qiuestions questions or no rice for you.

[grace10111]

usually a porus barrier blocks this, otherwise its VCE chemistry, you don't ask deep meaningful qiuestions questions or no rice for you.

hahah true

[crayolé]

Aha, heres the question i was referring to;

So the H+ ions are being reduced to H₂ reacting with F^- ions oxidised to F₂

If an Iron electrode is added, solutions say it will oxidise prferentially in place of the F^-. This is a spontaneous reaction and will occur even though we are trying to force the other reaction to go ahead?

[LinusX]

Yeah, so in this situation, you have H+ and F-. Circle these on your electrochemical series.
Realise that there is no water, so you'd expect F2 and H2 to be produced.

But if you use iron electrodes, you're going to get a negative gradient between H+ and
Fe (s). This means that a reaction will occur, thus interfering with the cell.

[masonnnn]

just had a mental blank.
with galvanic cells is it the same, left-reduction= you choose the highest up and right-oxidation= lowest, aslong as they produce a positive 'emf'?

[samiira]

just had a mental blank.
with galvanic cells is it the same, left-reduction= you choose the highest up and right-oxidation= lowest, aslong as they produce a positive 'emf'?

yup.. thats correct