The kinetics of the reactions between 1-bromopropane, 2-bromopropane, 1-bromobutane, 2-bromobutane, styrene and 2-propenylbenzene with H-atoms has been studied at 298 K in an isothermal discharge flow-reactor coupled to a quadrupole mass-spectrometer. Overall rate coefficients at a pressure of 4 mbar (1.6 mbar in the case of styrene and 2-propenylbenzene) were determined from the decrease of the concentrations of the bromo and of the aromatic hydrocarbons, respectively. The following values (in l mol1 s1) were obtained: 1-bromopropane, 2.3×107; 2-bromopopane, 2.3×107; 1-bromobutane, 2.4×107; 2-bromobutane, 2.8×107 ; styrene, 1.2×109; 2-propenylbenzene, 2.6×109. The reaction of styrene with hydrogen atoms has been used to generate chemically activated ethylbenzene. In the pressure range from 1 to 10 mbar the concentrations of the main products, toluene and ethylbenzene, were determined at several pressures. These measured concentration-pressure-profiles were discribed by a numerical simulation of an adequate mecanism. The ratio of the rate coefficients of the decomposition and of the stabilization of the activated ethylbenzene was calculated for each pressure by a corresponding least-squares fit with the values of the other rate coefficients kept fixed. From the pressure dependence of this ratio avarage exciting energies, avarage energies transferred per collision and collision efficiencies of the chemically activated ethylbenzene were obtained.