Lattice gas models are ideal for studying the properties of adsorbates
on inhomogeneous surfaces. The primary technique for examining these
models, Monte Carlo simulations, is often very computationally expensi
ve. We introduce an approximate theory that is well suited to rapidly
determining qualitative behaviours of lattice gases on inhomogeneous s
urfaces. This method is used to examine the effect of steps and kinks
on the well-studied A + B-2 model reaction. This reaction exhibits a d
iscontinuous and continuous kinetic phase transition on a perfect surf
ace. We show how these transitions behave as a function of terrace wid
th, step orientation, and surface diffusion rate.