Chapter 7: Chemical Reactions and Energy Flows

Hydrogen combustion produces only water as a byproduct and can be generated from renewable sources through electrolysis, with fuel cells offering particularly efficient energy conversion. The chapter then establishes core thermodynamic concepts, defining energy as the capacity to perform work and distinguishing between kinetic energy from particle motion and potential energy from intermolecular forces. The First Law of Thermodynamics establishes that energy cannot be created or destroyed within a closed system, with measurements standardized in Joules. Critical distinctions are drawn between temperature, which reflects average kinetic energy, and heat, the actual energy transfer between objects at different temperatures. Internal energy represents the total energy within a system and functions as a state variable, depending only on current conditions rather than the path taken. Enthalpy, defined as heat at constant pressure, provides a practical measure for reactions occurring under atmospheric conditions. The chapter classifies reactions as exothermic when they release energy to surroundings or endothermic when they absorb energy, with mathematical notation indicating these directions. Multiple methodologies for quantifying enthalpy changes are presented, including direct calorimetric measurement, Hess's Law for calculating enthalpy changes of complex reactions through summation of component steps, standard molar enthalpies of formation for individual substances, and bond energy estimation techniques. The chapter concludes by connecting these principles to biological systems, explaining how organisms extract energy through food oxidation and manage this energy via ATP synthesis and hydrolysis, demonstrating that thermochemical principles govern cellular metabolism and sustain life processes.