[Gobo]

Given:
- voltaic cell => spont. process ongoing
- Zn/Zn2+ half cell
- Ni/Ni2+ half cell
- [Ni2+] = 1.50M
- [Zn2+] = 0.1M
- En[cell]= 0.53 (I calculated this from the values given in my book. En[cell] is how I write standard cell potential by the way)

^- these are initial concentrations and these two electrodes are hooked up to create the voltaic cell
I already deduced from the S.E.P's that Zn species will constitute the anode, while the Ni species will constitute the cathode.

The question asks: What is [Ni2+] and [Zn2+] when the cell potential falls to 0.45V?

Attempt:[/b]
E[cell] = 0.45V

En[cell] = 0.53V

Please see my appproach below:

[Borek]

You are on the right track.

However, if it is a voltaic cell, solutions are separated. If so, you can't just use concentrations to calculate the stoichiometry. You may have to take both volumes into account, or assume they are identical.