This lecture focuses on the principles of thermodynamics as they relate to renewable energy. The instructor begins by discussing the internal energy of substances and its relationship to work and heat. Key terms such as enthalpy and entropy are introduced, emphasizing their importance in chemical reactions and material stability. The lecture explains how thermodynamic analysis can predict whether chemical reactions will occur and how materials respond to temperature changes. The instructor illustrates these concepts with practical examples, including the behavior of gases under pressure and the significance of energy transformations in combustion reactions. The discussion also covers the concept of enthalpy, defining it as the sum of internal energy and the product of pressure and volume. The instructor highlights the relevance of enthalpy in measuring heat exchange during chemical reactions, particularly at constant pressure. The lecture concludes with examples of combustion reactions, emphasizing the practical implications of thermodynamic principles in designing efficient energy systems.