  We study the spreading kinetics of a monolayer of hard-core particles on a
semi-infinite, chemically heterogeneous solid substrate, one side of which is
coupled to a particle reservoir. The substrate is modeled as a square lattice
containing two types of sites -- ordinary ones and special, chemically active
sites placed at random positions with mean concentration $\alpha$. These
special sites temporarily immobilize particles of the monolayer which then
serve as impenetrable obstacles for the other particles. In terms of a
mean-field-type theory, we show that the mean displacement $X_0(t)$ of the
monolayer edge grows with time $t$ as $X_0(t) = \sqrt{2 D_{\alpha} t \ln(4
D_{\alpha} t/\pi a^2)}$, ($a$ being the lattice spacing). This time dependence
is confirmed by numerical simulations; $D_{\alpha}$ is obtained numerically for
a wide range of values of the parameter $\alpha$ and trapping times of the
chemically active sites.
  We also study numerically the behavior of a stationary particle current in
finite samples. The question of the influence of attractive particle-particle
interactions on the spreading kinetics is also addressed.
