The reaction rates of para-substituted benzoyl chlorides ($p-CH_3$, p-H, $p-NO_2$) with pyridine have been measured employing the conductometry method in acetonitrile. The pseudo first-order and second-order rate constants were determined at various pressures and temperatures. The activation parameters (${Delta}V{ddagger},;{Delta}{eta}{ddagger},;{Delta}H{ddagger},;{Delta}S{ddagger},;{Delta}G{ddagger}$) and the Hammett ${ ho}$-values are determined from the values of rate constant. The values of ${Delta}V{ddagger},;{Delta}{eta}{ddagger};and;{Delta}S{ddagger}$ are all negative. The Hammett ${ ho}$-values are positive for the substrate (${ ho}_Y$) over the given pressure range. The results of kinetic studies, for the pressure and substituent changes, show that these reactions are proceeded by a typical $SN_2$reaction mechanism and its bond formation is favored with elevating pressure.