[en] A study has been made of electrochemical cells of the following type: Pb/PbSO₄/R₂(SO₄)₃x8H₂O+RCl₃x6H₂O/AgCl/Ag, where R is a rare-earth element. In this study have been use of neodymium and gadolinium compounds. The following reaction takes place at the electrochemical cell electrodes: Pbsub(solid)+SOsub(4(p-p))sup(2-)+2AgClsub(solid)=PbSOsub(4(solid))+2Agsub(solid)+2Clsub((p-p))sup(-), which determines the isobaric-isothermal potential (ΔG) variation occurring during operation of the electrochemical cell, for the following calculated reaction: 3Pbsub(solid)+6AgClsub(solid)+Rsub(2)(SOsub(4))sub(3)x8Hsub(2)Osub(solid)+4Hsub(2)Osub(liquid)=3PbSOsub(4(solid))+6Agsub(solid)+2RClsub(3)x6Hsub(2)Osub(solid). The basic thermodynamic functions calculated from this reaction are as follows: for Nd₂(SO₄)₃x8H₂O: ΔG₂₉₈⁰=-1295.8 kcal/mol, ΔH₂₉₈⁰=-1489.8 kcal/mol, S₂₉₈⁰=140.0 cal/molxdeg; for Gd₂(SO₄)₃x8H₂O: ΔG₂₉₈⁰=-1300.9 kcal/mol, ΔH₂₉₈⁰=-1489 kcal/mol, S₂₉₈⁰=157.6 cal/molxdeg