876:
the choice of ambient temperature and standard states, and is the result of the near-cancellation of certain terms in the expressions. For example, if a standard state of one atmosphere ideal gas is chosen for the electron gas then the cancellation of terms occurs at a temperature of 296 K, and the two definitions give an equal numerical result. At 298.15 K a near-cancellation of terms would apply and the two approaches would produce nearly the same numerical values. However, there is no fundamental significance to this near agreement because it depends on arbitrary choices, such as temperature and definitions of standard states.
768:
322:
Rockwood's approach to absolute-electrode thermodynamics is easily expendable to other thermodynamic functions. For example, the absolute half-cell entropy has been defined as the entropy of the absolute half-cell process defined above. An alternative definition of the absolute half-cell entropy has
875:
of the electron gas. The numerical value for the absolute potential of the standard hydrogen electrode one would calculate under the
Rockwood definition is sometimes fortuitously close to the value one would obtain under the Trasatti definition. This near-agreement in the numerical value depends on
214:
A different definition for the absolute electrode potential (also known as absolute half-cell potential and single electrode potential) has also been discussed in the literature. In this approach, one first defines an isothermal absolute single-electrode process (or absolute half-cell process.) For
314:
In this approach, all three species taking part in the reaction, including the electron, must be placed in thermodynamically well-defined states. All species, including the electron, are at the same temperature, and appropriate standard states for all species, including the electron, must be fully
870:
The types of physical measurements required under the
Rockwood definition are similar to those required under the Trasatti definition, but they are used in a different way, e.g. in Rockwood's approach they are used to calculate the equilibrium
586:
180:
472:
925:
Sergio
Trasatti, "The Absolute Electrode Potential: an Explanatory Note (Recommendations 1986)", International Union of Pure and Applied Chemistry, Pure & AppL Chem., Vol. 58, No. 7, pp. 955–66, 1986.
374:
This approach differs from the approach described by
Rockwood in the treatment of the electron, i.e. whether it is placed in the gas phase or the metal. The electron can also be in another state, that of a
851:
555:
46:
According to a more specific definition presented by
Trasatti, the absolute electrode potential is the difference in electronic energy between a point inside the metal (
514:
763:{\displaystyle E^{\ominus }{\rm {(H^{+}/H_{2})(abs)}}=\phi ^{\rm {Hg}}+\Delta _{S}^{\rm {Hg}}\psi _{\sigma =0}^{\ominus }-E_{\sigma =0}^{\rm {Hg}}{\rm {(SHE)}}}
573:
For practical purposes, the value of the absolute electrode potential of the standard hydrogen electrode is best determined with the utility of data for an
79:
1042:
Fang, Zheng; Wang, Shaofen; Zhang, Zhenghua; Qiu, Guanzhou (2008). "The electrochemical
Peltier heat of the standard hydrogen electrode reaction".
323:
recently been published by Fang et al. who define it as the entropy of the following reaction (using the hydrogen electrode as an example):
397:
319:
for the absolute electrode process. To express this in volts one divides the Gibbs free energy by the negative of
Faraday's constant.
779:
1100:
391:
The basis for determination of the absolute electrode potential under the
Trasatti definition is given by the equation:
895:
65:
is typically used for reference potential. The absolute potential of the SHE is 4.44 ± 0.02
525:
215:
example, in the case of a generic metal being oxidized to form a solution-phase ion, the process would be
62:
38:
measured with respect to a universal reference system (without any additional metal–solution interface).
1095:
885:
940:
Rockwood, Alan L. (January 1, 1986). "Absolute half-cell thermodynamics: Electrode potential".
927:
492:
1076:
1000:
949:
863:
8:
31:
1004:
953:
281:
175:{\displaystyle E_{\rm {(abs)}}^{M}=E_{\rm {(SHE)}}^{M}+(4.44\pm 0.02)\ {\mathrm {V} }}
1059:
1024:
1016:
973:
965:
890:
577:
380:
376:
316:
1051:
1008:
957:
23:
210:(SHE) denotes the electrode potential relative to the standard hydrogen electrode.
574:
558:
872:
1055:
1089:
1063:
1020:
1012:
969:
517:
961:
1028:
977:
311:
Other types of absolute electrode reactions would be defined analogously.
55:
47:
914:
61:
This potential is difficult to determine accurately. For this reason, a
58:
in which the electrode is submerged (an electron at rest in vacuum).
51:
254:
229:
991:
Rockwood, Alan L. (August 1, 1987). "Absolute half-cell entropy".
467:{\displaystyle E^{M}{\rm {(abs)}}=\phi ^{M}+\Delta _{S}^{M}\psi }
315:
defined. The absolute electrode potential is then defined as the
35:
27:
928:
http://www.iupac.org/publications/pac/1986/pdf/5807x0955.pdf
853:
is the absolute standard potential of the hydrogen electrode
70:
196:
66:
487:
is the absolute potential of the electrode made of metal M
846:{\displaystyle E^{\ominus }{\rm {(H^{+}/H_{2})(abs)}}}
782:
589:
528:
495:
400:
82:
257:electrode, the absolute half-cell process would be
845:
762:
549:
508:
466:
174:
999:(3). American Physical Society (APS): 1525–1526.
1087:
1041:
948:(1). American Physical Society (APS): 554–559.
915:IUPAC Gold Book – absolute electrode potential
73:. Therefore, for any electrode at 25 °C:
990:
939:
16:Electrode potential in electrochemistry
1088:
204:denotes the electrode made of metal M
550:{\displaystyle \Delta _{S}^{M}\psi }
207:(abs) denotes the absolute potential
13:
835:
832:
829:
814:
799:
752:
749:
746:
735:
732:
685:
682:
672:
662:
659:
642:
639:
636:
621:
606:
530:
447:
422:
419:
416:
167:
130:
127:
124:
98:
95:
92:
14:
1112:
386:
1070:
1035:
984:
933:
919:
908:
838:
826:
823:
795:
755:
743:
645:
633:
630:
602:
425:
413:
159:
147:
133:
121:
101:
89:
1:
901:
862:denotes the condition of the
41:
896:Standard electrode potential
383:and B. Damaskin and others.
20:Absolute electrode potential
7:
1050:(1–2). Elsevier BV: 40–44.
879:
379:in solution, as studied by
63:standard hydrogen electrode
10:
1117:
1101:Electrochemical potentials
1056:10.1016/j.tca.2008.04.002
886:Electrochemical potential
559:contact (Volta) potential
509:{\displaystyle \phi ^{M}}
1013:10.1103/physreva.36.1525
561:difference at the metal(
54:and a point outside the
962:10.1103/physreva.33.554
847:
764:
551:
510:
468:
192:is electrode potential
176:
1077:J. Electroanal. Chem.
848:
765:
552:
511:
469:
177:
1079:, 79 (1977), 259-266
864:point of zero charge
780:
587:
526:
493:
398:
80:
1005:1987PhRvA..36.1525R
954:1986PhRvA..33..554R
740:
711:
690:
575:ideally-polarizable
543:
460:
143:
111:
32:electrode potential
30:definition, is the
1044:Thermochimica Acta
843:
760:
715:
691:
671:
547:
529:
506:
464:
446:
172:
115:
83:
26:, according to an
993:Physical Review A
942:Physical Review A
891:Galvani potential
866:at the interface.
381:Alexander Frumkin
377:solvated electron
317:Gibbs free energy
164:
1108:
1096:Electrochemistry
1080:
1074:
1068:
1067:
1039:
1033:
1032:
988:
982:
981:
937:
931:
923:
917:
912:
861:
852:
850:
849:
844:
842:
841:
822:
821:
812:
807:
806:
792:
791:
769:
767:
766:
761:
759:
758:
739:
738:
729:
710:
705:
689:
688:
679:
667:
666:
665:
649:
648:
629:
628:
619:
614:
613:
599:
598:
580:(Hg) electrode:
556:
554:
553:
548:
542:
537:
516:is the electron
515:
513:
512:
507:
505:
504:
486:
473:
471:
470:
465:
459:
454:
442:
441:
429:
428:
410:
409:
367:
366:
365:
358:
357:
341:
339:
338:
335:
332:
304:
303:
302:
295:
294:
275:
273:
272:
269:
266:
246:
244:
243:
236:
235:
191:
181:
179:
178:
173:
171:
170:
162:
142:
137:
136:
110:
105:
104:
24:electrochemistry
1116:
1115:
1111:
1110:
1109:
1107:
1106:
1105:
1086:
1085:
1084:
1083:
1075:
1071:
1040:
1036:
989:
985:
938:
934:
924:
920:
913:
909:
904:
882:
873:vapour pressure
856:
817:
813:
808:
802:
798:
794:
793:
787:
783:
781:
778:
777:
742:
741:
731:
730:
719:
706:
695:
681:
680:
675:
658:
657:
653:
624:
620:
615:
609:
605:
601:
600:
594:
590:
588:
585:
584:
538:
533:
527:
524:
523:
500:
496:
494:
491:
490:
481:
455:
450:
437:
433:
412:
411:
405:
401:
399:
396:
395:
389:
370:
364:
362:
361:
360:
356:
354:
353:
352:
351:
349:
345:
336:
333:
330:
329:
327:
307:
301:
299:
298:
297:
293:
291:
290:
289:
288:
286:
279:
270:
267:
264:
263:
261:
249:
242:
240:
239:
238:
234:
232:
231:
230:
228:
226:
222:
189:
166:
165:
138:
120:
119:
106:
88:
87:
81:
78:
77:
44:
17:
12:
11:
5:
1114:
1104:
1103:
1098:
1082:
1081:
1069:
1034:
983:
932:
918:
906:
905:
903:
900:
899:
898:
893:
888:
881:
878:
868:
867:
854:
840:
837:
834:
831:
828:
825:
820:
816:
811:
805:
801:
797:
790:
786:
771:
770:
757:
754:
751:
748:
745:
737:
734:
728:
725:
722:
718:
714:
709:
704:
701:
698:
694:
687:
684:
678:
674:
670:
664:
661:
656:
652:
647:
644:
641:
638:
635:
632:
627:
623:
618:
612:
608:
604:
597:
593:
571:
570:
546:
541:
536:
532:
521:
503:
499:
488:
475:
474:
463:
458:
453:
449:
445:
440:
436:
432:
427:
424:
421:
418:
415:
408:
404:
388:
385:
372:
371:
368:
363:
355:
347:
343:
309:
308:
305:
300:
292:
284:
277:
251:
250:
247:
241:
233:
224:
220:
212:
211:
208:
205:
199:
195:V is the unit
193:
183:
182:
169:
161:
158:
155:
152:
149:
146:
141:
135:
132:
129:
126:
123:
118:
114:
109:
103:
100:
97:
94:
91:
86:
43:
40:
15:
9:
6:
4:
3:
2:
1113:
1102:
1099:
1097:
1094:
1093:
1091:
1078:
1073:
1065:
1061:
1057:
1053:
1049:
1045:
1038:
1030:
1026:
1022:
1018:
1014:
1010:
1006:
1002:
998:
994:
987:
979:
975:
971:
967:
963:
959:
955:
951:
947:
943:
936:
929:
922:
916:
911:
907:
897:
894:
892:
889:
887:
884:
883:
877:
874:
865:
859:
855:
818:
809:
803:
788:
784:
776:
775:
774:
726:
723:
720:
716:
712:
707:
702:
699:
696:
692:
676:
668:
654:
650:
625:
616:
610:
595:
591:
583:
582:
581:
579:
576:
568:
564:
560:
544:
539:
534:
522:
519:
518:work function
501:
497:
489:
484:
480:
479:
478:
461:
456:
451:
443:
438:
434:
430:
406:
402:
394:
393:
392:
387:Determination
384:
382:
378:
326:
325:
324:
320:
318:
312:
283:
260:
259:
258:
256:
245:
218:
217:
216:
209:
206:
203:
200:
198:
194:
188:
187:
186:
156:
153:
150:
144:
139:
116:
112:
107:
84:
76:
75:
74:
72:
68:
64:
59:
57:
53:
49:
39:
37:
33:
29:
25:
21:
1072:
1047:
1043:
1037:
996:
992:
986:
945:
941:
935:
921:
910:
869:
857:
772:
572:
569:) interface.
566:
562:
482:
476:
390:
373:
321:
313:
310:
252:
213:
201:
184:
60:
45:
19:
18:
565:)–solution(
69:at 25
56:electrolyte
48:Fermi level
1090:Categories
902:References
520:of metal M
348:(solution)
285:(solution)
225:(solution)
42:Definition
1064:0040-6031
1021:0556-2791
970:0556-2791
789:⊖
721:σ
713:−
708:⊖
697:σ
693:ψ
673:Δ
655:ϕ
596:⊖
545:ψ
531:Δ
498:ϕ
462:ψ
448:Δ
435:ϕ
154:±
52:electrode
880:See also
255:hydrogen
253:For the
50:) of an
1029:9899031
1001:Bibcode
978:9896642
950:Bibcode
773:where:
578:mercury
557:is the
477:where:
369:(metal)
344:2 (gas)
340:
328:
278:2 (gas)
274:
262:
221:(metal)
185:where:
1062:
1027:
1019:
976:
968:
163:
930:(pdf)
485:(abs)
306:(gas)
248:(gas)
36:metal
34:of a
28:IUPAC
22:, in
1060:ISSN
1025:PMID
1017:ISSN
974:PMID
966:ISSN
197:volt
157:0.02
151:4.44
1052:doi
1048:473
1009:doi
958:doi
860:= 0
346:→ H
223:→ M
1092::
1058:.
1046:.
1023:.
1015:.
1007:.
997:36
995:.
972:.
964:.
956:.
946:33
944:.
350:+
287:+
280:→
227:+
71:°C
1066:.
1054::
1031:.
1011::
1003::
980:.
960::
952::
858:σ
839:)
836:s
833:b
830:a
827:(
824:)
819:2
815:H
810:/
804:+
800:H
796:(
785:E
756:)
753:E
750:H
747:S
744:(
736:g
733:H
727:0
724:=
717:E
703:0
700:=
686:g
683:H
677:S
669:+
663:g
660:H
651:=
646:)
643:s
640:b
637:a
634:(
631:)
626:2
622:H
617:/
611:+
607:H
603:(
592:E
567:S
563:M
540:M
535:S
502:M
483:E
457:M
452:S
444:+
439:M
431:=
426:)
423:s
420:b
417:a
414:(
407:M
403:E
359:e
342:H
337:2
334:/
331:1
296:e
282:H
276:H
271:2
268:/
265:1
237:e
219:M
202:M
190:E
168:V
160:)
148:(
145:+
140:M
134:)
131:E
128:H
125:S
122:(
117:E
113:=
108:M
102:)
99:s
96:b
93:a
90:(
85:E
67:V
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