Abstract

New values are reported for the Gibbs energies of formation from the elements for hydrocerussite Pb(OH) 2 .(PbCO 3 ) 2 and hydrozincite [Zn(OH) 2 ] 3 .(ZnCO 3 ) 2 . These Delta G 0f , values were obtained from electrochemical cells without liquid junction. We determined Delta G 0f , [Pb(OH)2.(PbCO 3 ) 2 (s)] = -1699.8+ or -1.6 kJ/mol for hydrocerussite and Delta G 0f , {[Zn(OH) 2 ] 3 .(ZnCO 3 ) 2 } = -3163.3 + or - 4 kJ/mol for hydrozincite. These results allow future electrochemical cell experiments to be performed to determine the Delta G 0f , 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.

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