The reaction rate coefficients. k, for the reactions of ground-state Si+(P-2) with HCl, H2O, H2S, and NH3, have been measured as a function of reactant ion/reactant neutral center-of-mass kinetic energy, KE(CM), in a selected ion flow drift tube (SIFDT) apparatus, operated with helium at a temperature 298+/-2 K. The values k of the studied reactions have very pronounced, negative energy dependencies; the rate coefficients decrease by about 1 order of magnitude as KE(CM) increase from near thermal values to similar to 2 eV. The results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived complexes, These intermediate complexes decompose back to reactants or forward to products, the unimolecular decomposition rate coefficients for these reactions being k(1) and k(2), respectively, It is found that a power law of the form k(-1)/k(2)=const(KE(CM))(m) closely describes each reaction.