By means of the thermodynamics of irreversible processes, three thermoelectric quantities, namely, the Thomson coefficient, the Peltier coefficient, and the electromotive force of a thermocouple, are each expressed in terms of a pure temperature function h which is the difference between the isothermal energy flux in a conductor per unit electrical current and the electrochemical potential of the unit electrical charge. The Kelvin relations for the thermocouple follow directly.