Electrochemistry Cell question

[bchang57]

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Why is this correct?
Zn(s)|Zn2+||Cu2+|Cu(s)

and not this?
Cu(s)|Cu2+||Zn2+|Zn(s)

for a Daniell Cell?


does anyone know why can't Zinc be reduced instead of Cu? Achiever doesn't really say

 

[facecrime]

you have to look at E knot (standard) value for both copper and zinc from the activity series. smaller number gets oxidized..i think

 

[ttpharm]

Look at the reduction potentials Eknot. The one with the highest number will be the one that gets reduced because its the most spontaneous.

Remember dG=-nFE and the more negative dG is the more spontaneous it is.

So if one value is -.9 V and the other is -.8V then the element being reduced with the -.8 V will be the one you leave being reduced and you change the other element with -.9V to being oxidized. When you analyze the dG value -> .8 < .9 and .8 is closer to being negative and therefore more spontaneous.

Hope this helps..

 

[hamptongirl]

Why is this correct?
Zn(s)|Zn2+||Cu2+|Cu(s)

and not this?
Cu(s)|Cu2+||Zn2+|Zn(s)

for a Daniell Cell?


does anyone know why can't Zinc be reduced instead of Cu? Achiever doesn't really say

Daniell Cell is a type of Galvanic/Voltaic Cell which is spontaneous so Ecell > 0

Reduction potentials:
Zn2+ + 2&#8202;e&#8722; &#8594; Zn(s) -0.76V
Cu2+ + 2&#8202;e&#8722; &#8594; Cu(s) +0.34V

For the reaction to have a + Ecell, Zn must be oxidized (+0.76V) and Cu2+ must be reduced (+0.34V). Ecell = reduction potential + oxidation potential = 0.76V + 0.34V = 1.10V


Shorthand Notation for galvanic cell: Anode/oxidation || Cathode/reduction
|| represents the salt bridge


Zn is OXidized at the ANode.
Cu2+ is REDuced at the CAThode.

Zn(s)|Zn2+||Cu2+|Cu(s)


why can't Zinc be reduced instead of Cu?
If Zn2+ is reduced (Note: Zn cannot be reduced ie gain electrons), Cu is oxidized.
Ecell = reduction potential + oxidation potential = -0.76V + -0.34V = -1.10V
If Ecell < 0 then this reactions is not spontaneous and it cannot be a Daniell Cell/ Galvanic/Voltaic Cell.