## Ways to Calculate Standard Cell Potentials

Baoying Li 1B
Posts: 113
Joined: Sat Aug 17, 2019 12:18 am

### Ways to Calculate Standard Cell Potentials

If I am correct, there are two ways to calculate the Stand Cell Potentials. The first way is to use Le Chatelier's Law, adding the standard potentials of the reactions. The second way is to use the formula Standard Cell Potentials = Standard Potential of Cathode - Standard Potential of Anode. But when do we need to reverse one of the reactions and change the sign of the standard potentials of one of the reactions?

Uisa_Manumaleuna_3E
Posts: 60
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Ways to Calculate Standard Cell Potentials

You only reverse one of the reactions and change the sign of one of the standard potentials with the first method. If you try reversing and changing the signs with the second method, you get a different value entirely.

Chris Tai 1B
Posts: 102
Joined: Sat Aug 24, 2019 12:16 am

### Re: Ways to Calculate Standard Cell Potentials

Concerning the second method of calculating standard cell potentials - When you get the value of the standard cell potential, you'll always get a positive E value because the reduction of an element is spontaneous. However, some of the elements are oxidized, and you often won't find a standard cell potential value that gives you the right sign. All you have to do is multiply the positive E value by negative 1 when you have a redox reaction for the element that is being oxidized in the reaction.
This is similar to the example that Professor Lavelle went over regarding Copper (II) and Zinc.

Angela Prince 1J
Posts: 102
Joined: Sat Aug 24, 2019 12:17 am

### Re: Ways to Calculate Standard Cell Potentials

Uisa_Manumaleuna_3E wrote:You only reverse one of the reactions and change the sign of one of the standard potentials with the first method. If you try reversing and changing the signs with the second method, you get a different value entirely.

Conceptually, why can you not reverse the cell potential value of the reversed reaction?