Gas-liquid scattering, D --> H exchange, and time-dependent uptake measurements are used to follow HCl, DCl, and HBr as they strike the surface of the neutral, hydrogen-bonding liquid glycerol. In this and the following paper, we report studies of gas-liquid energy transfer and trapping, the nature of HCl and HBr interfacial and bulk phase dissociation and recombination, and the thermodynamics of HCl solvation. We find that most HCl and HBr molecules readily dissipate their excess kinetic energy and thermalize at the surface of glycerol, even at impact energies up to 100 U mol(-1) and glancing angles of incidence up to 60degrees. Nearly all thermally accommodated HBr molecules dissolve in glycerol for longer than 10 S. HCl is less acidic and dissolves reversibly for times of 0.1 to 1 s at incident HCl fluxes of (2 to 0.2) x 10(15) cm(-2) s(-1), respectively. Experiments utilizing DCl show that this reversible solvation is accompanied by dissociation into D+ and Cl-, D+ --> H+ exchange, and HCl desorption. The residence times of HCl in glycerol and their temperature dependences yield DeltaG(HCl)degrees(gly) = -19 +/- 2 kJ mol(-1), Delta(HCl)degrees(gly) = -67 +/- 4 kJ mol(-1), and DeltaS(HCl)degrees(gly) 165 +/- 20 J mol(-1) K-1 for HCl(g) reversible arrow H+(gly) + Cl-(gly) at 294 K.