chemical thermodynamics of neptunium and plutonium - U.S. ...

2.1 Symbols, terminology and nomenclature 192.1.6.4 Equilibria involving the addition of a gaseous ligandA special notation is used for constants describing equilibria that involve the additionof a gaseous ligand, as outlined in Eq. (2.20).ML q−1 + L(g) Å ML q K p,q = [ML q](2.20)[ML q−1 ]p LThe subscript “p” can be combined with any other notations given above.Example:CO 2 (g) Å CO 2 (aq) K p = [CO 2(aq)]p CO23UO 2+2+ 6CO 2 (g) + 6H 2 O(l) Å (UO 2 ) 3 (CO 3 ) 6−6+ 12 H +∗ β p,6,3 = [(UO 2) 3 (CO 3 ) 6−6 ][H+ ] 12[UO 2+2 ]3 p 6 CO 2UO 2 CO 3 (cr) + CO 2 (g) + H 2 O(l) Å UO 2 (CO 3 ) 2−2+ 2H +∗ K p,s,2 = [UO 2(CO 3 ) 2−2 ][H+ ] 2p CO2In cases where the subscripts become complicated, it is recommended that K or β beused with or without subscripts, but always followed by the equation number of theequilibrium to which it refers.2.1.6.5 Redox equilibriaRedox reactions are usually quantified in terms of their electrode (half cell) potential,E, which is identical to the electromotive force (emf) of a galvanic cell in which theelectrode on the left is the standard hydrogen electrode, SHE 1 , in accordance withthe “1953 Stockholm Convention” [88MIL/CVI]. Therefore, electrode potentials aregiven as reduction potentials relative to the standard hydrogen electrode, which actsas an electron donor. In the standard hydrogen electrode, H 2 (g) is at unit fugacity (anideal gas at unit pressure, 0.1 MPa), and H + is at unit activity. The sign of the electrodepotential, E, is that of the observed sign of its polarity when coupled with the standardhydrogen electrode. The standard electrode potential, E ◦ , i.e. the potential of a standardgalvanic cell relative to the standard hydrogen electrode (all components in theirstandard state, cf. Section 2.3.1, and with no liquid junction potential) is related to thestandard Gibbs energy change r G ◦ m and the standard (or thermodynamic) equilibriumconstant K ◦ as outlined in Eq. (2.21).E ◦ =− 1nF rG ◦ m = RTnF ln K ◦ (2.21)1 The definitions of SHE and NHE are given in Section 2.1.1.