THE TRANSPORTED ENTROPY OF NA-STATE CRYOLITE( IN SOLID)

The transported entropy of Na+ in mixtures of NaF (s) and Na(3)A1F(6) (s) is determined from thermocell experiments. The experiments were fa vorably described by the electric work method. The variation observed in the thermocell electromotive force (emf) with composition can be ex plained from the probable path of charge transfer in the electrolyte. The transported entropies are S(cry)(Na+) = 140 +/- 7 J K-1 mol(-1) f or cryolite and S(NaF)(Na+) = 81 +/- 8 J K-1 mol(-1) for sodium fluor ide between 380 degrees C and 500 degrees C. The value obtained for so dium in the solid cryolite makes us predict that the transported entro py for Na+ in the molten electrolyte mixture for aluminum production i s substantial and that the reversible heat effects in the aluminum ele ctrolysis cell are the same.