306 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



corresponds to an increase in the ionization of these electrolytes with the 

 temperature. This is not in agreement with the observed results of 

 conductance measurements. It is possible, however, that the energy 

 change measured on the dilution of a solution includes effects other than 

 those due to change in the ionization of the electrolyte. Certainly, at 

 the higher concentrations, it is to be expected that a change in the 

 hydration of the ions, and possibly of the neutral molecules, takes place, 

 and the energy change accompanying these processes may obscure the 

 energy change due to the ionization process. 



It appears, thus, that a knowledge of the thermal properties of elec- 

 trolytic solutions has a very direct bearing on our interpretation of the 

 phenomena observed in electrolytic solutions. In order to analyze the 

 more or less complex processes into their constituent effects, however, 

 further experimental data are required. 



In this connection, it should also be noted that a number of investi- 

 gators, 38 from a study of the temperature coefficient of the electromotive 

 force of concentration cells, have obtained values for the energy changes 

 accompanying the transfer of electrolytes from solutions of one concen- 

 tration to another. Harned has also determined the energy changes 

 accompanying the transfer of hydrochloric acid from a solution con- 

 taining a mixture of salt and acid to one containing acid alone. Hydro- 

 chloric acid and chlorides were employed in these mixtures. 



In the following table are given values of the energy change accom- 

 panying the transfer of one mol of electrolyte from the concentration 

 given to a concentration of 0.1 N, according to Ellis and Harned. 



TABLE CXXVI. 



ENERGY CHANGE, IN JOULES, ACCOMPANYING THE TRANSFER OF ONE 

 MOL OF ELECTROLYTE FROM A CONCENTRATION C TO A CON- 

 CENTRATION 0.1 N AT 25. 



C KC1 NaCl HC1 



0.1000 000 000 000 



0.3000 355 300 420 



0.5000 650 570 820 



1.000 1310 1196 1820 



1.500 1900 1780 2770 



2.000 2375 2300 3720 



2.500 2810 2690 4740 



3.000 3175 3010 5710 



As may be seen from the table, the energy changes accompanying the 

 transfer of sodium and potassium chlorides differ but little. The sign of 



"Ellis, J. Am. CUem. Soc. 38, 737 (1916) ; Harned, ibid., # t 1808 (1920). 



