determining cathode from anode

[Abigail Urbina 1K]

If we are given two half reactions with their standard cell potentials, how exactly are we supposed to know which is the cathode and which is the anode, and thus which reaction we would need to reverse?

For example on question 3C of the 2014 Final:
Fe3+ + e- --> Fe2+
Zn2+ + 2e- --> Zn(s)

It says that the second reaction is the anode and the first reaction is the cathode. How are we sure of this?

[Michaela Capps 1l]

You would look at the standard cell potentials. The most positive is the cathode. Also, cathode-(anode) should be positive.

[Curtis Wong 2D]

I am pretty sure that the only way to determine the cathode from the anode is based on their standard cell potential. Cathodes are the ones that are reduced and the the Anodes are the ones that are being oxidized. And we know our Galvanic cell needs to be a positive number so whichever combination of the two leads to the greatest positive cell potential determines the anode and cathode.

[Michael Downs 1L]

It is similar to the reducing and oxidizing agents

[Rishi Khettry 1L]

Calculate cathode - anode substituting both numbers and the combination that gives the most positive output is the correct one

[snehabhargava]

Check the standard cell potentials.

[Gwen Peng 1L]

The final most likely had a sheet with all of the standard cell potentials which then allows you to determine your anode and cathode. The anode is always the half reaction that has a more positive standard cell potential (higher voltage) because it will be flipped and the sign will become negative, therefore once it is plugged into the equation E standard (cell)= E standard (cathode) - E standard (anode) the double negative will turn into addition.

[Caroline LaPlaca]

RED CAT= reduced cathode

[Troy Tavangar 1I]

The one with the greater cell potential is the cathode.

[Megan_Ervin_1F]

Also it is just standard for the anode to appear on the left

[haleyervin7]

Also it is just standard for the anode to appear on the left

You can remember this because it is alphabetical from left to right (anode-cathode).

[805087225]

The cathode is where it is reduction, and thus, the potential will be positive(because it is always written in terms of reduction potential) and the other one will be the anode(which causes oxidation to occur - loss of electrons which we can see from the equation given), and thus we know that is the one to reverse.