Gibbs energies of formation for hydrocerussite [Pb(OH)2 · (PbCO3)2(s)] and hydrozincite {[Zn(OH)2]3 · (ZnCO3)2(s)} at 298 K and 1 bar from electrochemical cell measurements

• Published in: The American mineralogist 1998-07, Vol.83 (7), p.739-745
• Main Authors: Mercy, M. A., Rock, Peter A., Casey, William H., Mokarram, Mehdi M.
• Format: Article
• Language: English
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am-1998-7-806

New values are reported for the Gibbs energies of formation from the elements for hydrocerussite Pb(OH) · (PbCO and hydrozincite [Zn(OH) · (ZnCO . These ΔG values were obtained from electrochemical cells without liquid junction. We determined ΔG [Pb(OH) · (PbCO (S)] = -1699.8 ± 1.6 kJ/mol for hydrocerussite and ΔG ([Zn(OH) · (ZnCO ) = -3163.3 ±4 kJ/mol for hydrozincite. These results allow future electrochemical cell experiments to be performed to determine the ΔG values of other hydroxycarbonate minerals using either the Pb amalgam-hydrocerussite or the Zn amalgam-hydrozincite as reference electrodes. These reference electrodes provide a strategy for establishing Gibbs energies for phases with two different anions, which are geochemically interesting but difficult to study experimentally.