ABSTRACT
Thermodynamics provides an essential accounting method to check that kinetic schemes are internally consistent and to ensure that a proposed mechanism does not correspond to a perpetual motion device. This chapter examines the theories behind the time scale of chemical reactions and how these ideas have been adapted to biopolymers. It also presents an introduction to other concepts of physical chemistry that are important in understanding the properties of biological macromolecules. A spontaneous reaction requires no external energy input for it to occur; it is a downhill process. Enthalpy changes alone cannot predict whether a chemical reaction will be spontaneous. For many biochemical calculations, it is safer to work with equilibrium constants rather than standard free energies, because keeping track of units is more important than simplifying a multiplication problem to one of addition. Free energy, G, and enthalpy, H, are extensive state functions; i.e., their values depend on the amount of substance present.
