The authors investigate the kinetics of a generalized monomer-monomer surface reaction model in which there is a variable excluded-volume interaction between same species particles (As and Bs). For no interaction, this system reduces to the monomer-monomer model for which there is a first-order transition between A- and B-saturated phases. As a function of the excluded volume interaction, the first-order transition line for weak interaction terminates at a tricritical point where two second-order transitions meet. These transitions, which appear to be in the Reggeon field theory universality class, separate the A-saturated, reactive, and B-saturated phases. Series expansions and various time-dependent Monte Carlo simulations are used to estimate the critical parameters and exponents associated with these transitions.