5 Equilibrium, Rate, and Natural Systems

Publisher Summary This chapter examines the physical principles used to describe chemically reactive systems. The conditions under which systems are considered fall into two categories: (1) the system may be at thermodynamic equilibrium with no input or output of energy and (2) energy inputs do exist and the system may or may not be changing. The chapter reviews the thermodynamic principles necessary to describe equilibrium systems. The First Law (the energy conservation law) introduces H, the enthalpy, as a state function of a system. State functions depend only on the state of the system and not on the way it managed to arrive at that state. The Second Law (the entropy law) introduces entropy, S, as a state function. More importantly, this law also describes the equilibrium state of a system as one of maximum entropy. A discussion of electrochemistry is also included. The rates of chemical changes, or chemical kinetics, are examined. The chapter also examines selected natural systems in which thermodynamic and kinetic factors are important.