The range of chemical problems that are directly accessible to first-principles molecular dynamics simulations based on density functional theory is extended with a novel method apt to accelerate rare reactive events. The introduction of a finite electronic temperature within the Mermin formalism leads to a lowering of chemical activation barriers and thus to an exponential enhancement of the rate at which these reactions are observed during a first-principles molecular dynamics simulation. The method presented here makes direct use of the intrinsic chemical information encoded in the electronic structure, and is therefore able to lower selectively chemically relevant activation energies even in systems where many competing low-energy pathways for conformational transitions or diffusive motions are present. The performance of this new approach is demonstrated for a series of prototypical chemical reactions in gas and in condensed phase. A typical acceleration that can be achieved is, for example, a factor of 10(5) for the cis-trans isomerization of peroxynitrous acid in aqueous solution at room temperature.