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# Chemistry Q help, calculating standard electrode potentials watch

1. How do you calculate standard electrode potentials? I don't understand them

What I have been told to do:
• Change the sign of the most negative number/least postive number
• Add the 2 number values that I obtained from the data booklet together

I tried that and I don't think its correct. I asked for help but now I just think I'm annoying my teachers!

so, any help?

Here is an example:

Zn2+(aq) + 2e- ⇌ Zn(s) E cell value: -0.76
VO2+(aq) + 2H+(aq) +e- ⇌ V3+ (aq) + H2O(l)
E cell value: +0.34V

This is what I would do:
Change the Zn sign because its going towards the left hand side, to make it +0.76
(+0.76) + (+0.34) = 1.1v

Am I right?

If any of you have the A2 edexcel book, you can also look at page 176. I need help with the (Sc) yellow box at the top please!

Thanks,
2. the equation

Total E cell: E cell on right hand - E cell on left hand only works for the equations in the proper form right?
3. (Original post by Preziosavita)
How do you calculate standard electrode potentials? I don't understand them

What I have been told to do:
• Change the sign of the most negative number/least postive number
• Add the 2 number values that I obtained from the data booklet together

I tried that and I don't think its correct. I asked for help but now I just think I'm annoying my teachers!

so, any help?

Here is an example:

Zn2+(aq) + 2e- ⇌ Zn(s) E cell value: -0.76
VO2+(aq) + 2H+(aq) +e- ⇌ V3+ (aq) + H2O(l)
E cell value: +0.34V

This is what I would do:
Change the Zn sign because its going towards the left hand side, to make it +0.76
(+0.76) + (+0.34) = 1.1v

Am I right?

If any of you have the A2 edexcel book, you can also look at page 176. I need help with the (Sc) yellow box at the top please!

Thanks,
The magnitude of the voltage can be easily found by finding the difference between the two values....

e.g. +0.45 and -0.20 will give a voltage of 0.65V

The direction depends upon which way you define the current flow.
I remember which way round the current will flow by using the reduction potentials. A positive potential means the process described (adding an electron) is favourable. So the electrons will flow to the electrode with the most positive electrode potential and away from the most negative (can and often is a positive value also)

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