Chem Q

[ATLATLATL]

for the galvanic cell half rxns can someone plz tell me how to figure out when there is a sign change...
is it that the more favorable reduction reaction remains positive...and that the one that is most negative thus will become positive...c wat i mean...lost
like say for instance the oxidation of mn~>mn2+ 1.03
and the oxidation of mg~>mg2+ is 2.37
cu~>cu2+ is -.16

what would i do exactly?

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[jdmsamurai]

those are simply reduction potentials...if they have a "high" (positive) reduction potential then they will likely be "reduced" becoming more negative....
and the other sign is switch to a positive...
remember

G = - EMF * N * F and its always negative for galvanic cells making it spontaneous

example

Ag+ + e ---> Ag(s) E = .80
Tl + e ----> Tl(s) E = -.34

since Ag has a "higher" reduction potential it will be reduced...so you keep that and switch the second equation into
Tl(s) ----> Tl + e E = .34

now add the reduction potentials and you get .34 + .8 = 1.04