  We study the kinetics of diffusion-limited coalescence, A+A->A, and
annihilation, A+A->0, in random media consisting of disconnected domains of
reaction. Examples include excitons fusion and annihilation in porous matrices
and along polymer chains. We begin with an exact analysis of A+A->A in a finite
segment. This result is applied to coalescence in a random distribution of
segment lengths, and the implications for coalescence and annihilation in
percolation clusters and other confined geometries are then derived by means of
scaling techniques.
