  Wetting and dewetting dynamics of simple and complex liquids is described by
kinetic equations in gradient dynamics form that incorporates the various
coupled dissipative processes in a fully thermodynamically consistent manner.
After briefly reviewing this, we also review how chemical reactions can be
captured by a related gradient dynamics description, assuming detailed balanced
mass action type kinetics. Then, we bring both aspects together and discuss
mesoscopic reactive thin-film hydrodynamics illustrated by two examples,
namely, models for reactive wetting and reactive surfactants. These models can
describe the approach to equilibrium but may also be employed to study
out-of-equilibrium dynamics. In the latter case, one breaks the gradient
dynamics form by chemostatting to obtain active systems. In this way, for
reactive wetting we recover running drops that are driven by chemically
sustained wettability gradients and for drops covered by autocatalytic reactive
surfactants we find complex forms of self-propulsion and self-excited
oscillations.
