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Theelectrochemicalreactionsinthegalvaniccellproceedspontaneously,i.e.:
ΔG=-zF·EMF<0
(1.13)
where:
ΔG-changeofthermodynamicpotentialassociatedwiththecourseofelectrochemical
reactionsinanopengalvaniccell,
EMF=E
oC–E
oA>0-electromotiveforce(opengalvaniccell).
1)Zn/ZnSO
Examplesofgalvaniccells:
4//CuSO
4/Cu:
-Thefollowingreactionstakeplaceinthiscell:
•anodic:
ZnąZn2++2e,
2)Zn/ZnSO
•cathodic:
4//H
2SO
4/Cu:
Cu2++2eąCu;
-Thefollowingreactionstakeplaceinthiscell:
•anodic:
ZnąZn2++2e,
2H++2eąH
2.
•cathodic:
Thepolarizationcurvesforthetwo-electrodesystem(galvaniccellorelectrolysis)are
plottedinFigure1.6.
I
I
I
sc
x
C
1
η
C1
E
η
A1
o1
C
U=I(R+R)
2
gc
U
x
sc
EMF
A
E
1
I
η
C2
E
η
o2
A2
A
2
E
Fig.1.6.Polarizationcurvesintwoelectrodesystem(galvaniccellorelectrolysis):
I
x
-appliedcurrentintensity
I
sc
-intensityofshort-circuitcurrent(electrodesindirectcontact,e.g.corrosioncell)
U
U
sc
gc
-voltageofworkinggalvaniccell
-short-circuitvoltage,U
sc=I
scR
I
R
I
–„internal”resistance(resistanceofelectrolyte)
R
E
–„external”resistance(resistanceofexternalwiresconnectingbothelectrodes)
E
o1;E
o2
-equilibriumpotentialsof1and2electrode,respectively
EMF-electromotiveforce,EMF=E
o2-E
o1
η
A1;η
C1-anodicandcathodicoverpotentialsrelatedtocurrentintensityI
xforelectrode1
η
A2;η
C2-anodicandcathodicoverpotentialsrelatedtocurrentintensityI
xforelectrode2
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