Introduction

In this chapter we begin our study of kinetic phenomena in materials. We should become knowledgeable about concepts common to all kinetic phenomena in condensed matter. In gases, molecules come into contact by collision processes. In condensed matter, the atoms or molecules oscillate or rotate about a stable position or orientation, at any finite temperature. Even at 0 K they perform a zero point motion. These oscillations or rotations make possible the existence of kinetic phenomena in condensed matter. Each such phenomenon involves the motions of atoms or molecules in some particular way, which we will describe as a motion along a reaction path. If the energy of the system passes through a maximum as these particles move along the reaction path, then we describe this maximum energy as an activation energy , which the system must exceed for it to proceed from its initial state to a different state along this reaction path. Since there are many reaction paths from reactant state to product state, the path with the highest probability of being followed is that involving the least activation free energy, which is usually called the saddle point energy. We shall explore the deeper significance of the activation energy in this chapter.

Kinetic phenomena that occur not too far from equilibrium conditions can be treated using linear approximations to rate relations. The linear realm including concepts from reaction rate theory and the thermodynamic theory of irreversible processes comprises the scope of this chapter. The non-linear regime applicable to far...