Clasical thermodynamic analysis of any thermal and chemical process is usually based on the first law of thermodynamics. Such an approach is not sufficient when deeper understanding of the mechanism and nature of each elementary process is required. The use of the first and second law of thermodynamics together is necessary to solve practical problems more effectivly. Especially, application of the entropy generation rate and lost available energy (or exergy) concepts enhance our understanding of thermal process. Such an extended analysis is proposed to detect possible ways to decrease the electric energy consumption. Additionally, least squares adjustment procedure is proposed to make mathematical models of elementary processes taking place inside electrolysis cell more reliable.