A Study of the Heat Effects at Electrodes During Electrolysis

Temperature difference measurements were made during the electrolysis of aqueous copper sulfate between copper electrodes. The temperature differences measured were those between the cathode and the anode, the cathode solution, and the anode and the solution. These values were obtained as a function of the time of the electrolysis. The variation of these differences with time and their magnitudes were explained in terms of the entropy changes occurring at the electrodes, resistance, and polarization.

The effect of some inert electrolytes on these temperature differences was determined as was the effect of gelatin. Explanations for these effects were given in terms of polarization and the thermodynamics of irreversible processes as applied to thermocells.

It was found that these temperature differences were extremely dependent on, and had a definite relationship to, the concentration of the copper sulfate solutions. Accordingly, a method was proposed whereby such temperature differences could be used as an analytical method. This method was given the name, "Thermal Electroanalysis."

A theoretical analysis was made of the quantity of heat evolved by an electrochemical reaction during electrolysis. This analysis was made from the standpoint of the thermodynamics of irreversible processes and its relationship to classical thermodynamics was indicated.

A calorimetric method was developed which made it possible to measure the amount of heat liberated at a single electrode during an electrochemical reaction. It was also possible to measure the total amount of heat liberated by the same electrochemical reaction. These data, coupled with the theoretical analysis, made it possible t calculate the enthalpy change for the total reaction as well as the entropy change occurring at each electrode. This was done for the copper-aqueous copper-sulfate-copper and silver-aqueous silver nitrate-silver systems at three different concentrations of electrolyte for each system.

The values obtained for these systems were compared with the existing literature data where possible. Certain differences were pointed out in the case of the entropy values, especially their variation with concentration. Explanations were postulated for these differences and further work was proposed to clarify these points.

In order to test the calorimetric technique and to prove the validity of the method, the enthalpy change for the decomposition of water was measured by this combination of calorimetric and electrochemical techniques. The values obtained were in very good agreement with the accepted value for this quantity. This was considered to be sufficient proof that this technique is a valuable tool for obtaining thermodynamic data which is extremely difficult to obtain by other means.