  Motion of chemically driven droplets is analyzed by applying a solvability
condition of perturbed hydrodynamic equations affected by the adsorbate
concentration. Conditions for traveling bifurcation analogous to a similar
transition in activator-inhibitor systems are obtained. It is shown that
interaction of droplets leads to either scattering of mobile droplets or
formation of regular patterns, respectively, at low or high adsorbate
diffusivity. The same method is applied to droplets running on growing terrace
edges during surface freezing.
