  Aqueous solutions provide a medium for many important reactions in chemical
synthesis, industrial processes, environmental chemistry, and biological
functions. It is an accepted fact that aqueous solvents can be direct
participants to the reaction process and not act only as simple passive
dielectrics. Assisting water molecules and proton wires are thus essential for
the efficiency of many reactions. Here we study the decomposition of urea into
ammonia and isocyanic acid by means of enhanced ab initio molecular dynamics
simulations. We highlight the role of the solvent molecules and their
interactions with the reactants providing a proper description of the reaction
mechanism and how the water hydrogen-bond network affects the reaction
dynamics. Reaction free energy and rates have been calculated taking into
account this important effect.
