Reaction between SiO2 and water has been studied extensively using ab initio methods. The mechanism for formation of metasilicic acid SiO(OH)(2) and orthosilicic acid Si(OH)(4) has been explored and a new pathway for formation of Si(OH)(4) is predicted. Heats of reaction (Delta H-r(298)circle) and heats of formation (Delta H-f(298)circle) at 298 K for the related reactions and species calculated at two different theoretical levels G3B3 and G3MP2B3 agree well with the literature values. It is found that when SiO2 reacts simultaneously with two water molecules, the thermodynamic as well as kinetic feasibility of the process is much greater than that when SiO2 reacts with one molecule of water. (C) 2009 Elsevier B. V. All rights reserved.