## Ecell values

Sarah Blake-2I
Posts: 153
Joined: Fri Aug 30, 2019 12:16 am

### Ecell values

How can you tell which half reaction is being reduced or oxidized based on the Ecell value? There was a question like this on test 2 and I am confused as to how you would distinguish this based on just the standard potential value.

Christine Honda 2I
Posts: 116
Joined: Sat Sep 14, 2019 12:17 am

### Re: Ecell values

The higher Ecell value is usually reduced!

Nicholas Chin 1G
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

### Re: Ecell values

You can use the appendix to look at the E values for the two half reactions. Since the equation for Ecell is E(c) = E(cath) - E(anode), then you can determine which reaction is cathode and which one is anode.

Amanda Lin 2I
Posts: 101
Joined: Sat Aug 17, 2019 12:15 am

### Re: Ecell values

The one with a higher, more positive Ecell value is usually reduced while the one with a lower, more negative Ecell value is usually oxidized.

jisulee1C
Posts: 149
Joined: Thu Jul 25, 2019 12:17 am

### Re: Ecell values

Since most tables give the reduction potential for the half reaction, the higher (more positive) reduction potential determines the cathode which is the species that will undergo reduction.

Deena Doan 2F
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

### Re: Ecell values

the one that has a higher (more positive) value is usually the one that is reduced aka the cathode

Ryan Yee 1J
Posts: 101
Joined: Sat Aug 17, 2019 12:16 am

### Re: Ecell values

The more positive value is reduced so that when you subtract the anode's value it'll remain positive

Simon Dionson 4I
Posts: 107
Joined: Sat Sep 14, 2019 12:17 am

### Re: Ecell values

along with the responses above, I also try to consider which assignment of the cathode or anode will result in a positive Eº cell value

Rafsan Rana 1A
Posts: 55
Joined: Sat Aug 24, 2019 12:16 am

### Re: Ecell values

In addition to the answers given, the reason we want to have a positive E cell is because it leads to a negative standard gibbs free energy which in turn means a positive value for entropy meaning the process is spontaneous.

Rhea Shah 2F
Posts: 97
Joined: Thu Jul 25, 2019 12:17 am

### Re: Ecell values

The more positive E cell value corresponds to the reaction that is reduced. This reaction occurs at the cathode.

Diana A 2L
Posts: 106
Joined: Sat Aug 17, 2019 12:16 am
Been upvoted: 1 time

### Re: Ecell values

If you take the reverse of a reaction, does the sign of the Ecell also flip, or does it remain? For example, when constructing redox reactions from redox couples you are given, you determine which couple is at the anode and at the cathode by examining Ecell values. You set up the reaction in a way that yields a positive Ecell based on the corresponding cell potentials. Determining which redox couple is the anode and cathode also allows you to figure out what is being oxidized and what is being reduced.

Once you know which half-reaction is being oxidized, you flip it for the overall reaction (ex: Zn(2+) + 2e- ==> Zn(s) becomes Zn(s) ==> Zn(2+) + 2e) When the reaction is flipped, does the cell potential sign change too??

Aiden Metzner 2C
Posts: 104
Joined: Wed Sep 18, 2019 12:21 am

### Re: Ecell values

The higher Ecell value is usually reduced because the E cell values are the standard values of reduction. One that produces a higher value that is reduced is more likely to be reduced in a reaction.

Charysa Santos 4G
Posts: 107
Joined: Wed Sep 18, 2019 12:21 am
Been upvoted: 1 time

### Re: Ecell values

The more positive/less negative Ecell value is typically correlated to the cathode (reduced), and the more negative Ecell value is correlated to the anode (oxidized).