Electronic structure calculations are used to derive thermodynamics data for the reaction Q(center dot) + H-2 --> QH + H-center dot, where Q(center dot) is a spin-1/2 radical. Data are obtained both for the gas and aqueous phase. Analysis of scaled relative free energy-and enthalpy changes for a set of 29 radicals inspires introduction of a radicalicity scale. This scale offers a simple measure of the reactivities of the different radicals. (C) 2014 Elsevier B.V. All rights reserved.