Silica based materials are important candidates as anodes for lithium ion batteries due to their high specific capacity, low production and material cost and abundance in the earth crust. Silica lithiation leads to reversible and irreversible reactions to produce silicon, lithium oxide and lithium silicates. The final composition of these products confers a variety of electrochemical performances, particularly concerning their specific capacity and stability/cyclability of the electrodes. Knowledge on the thermochemistry of these reactions is relevant to analyze the thermodynamic stability and potential occurrence of the different phases. In this work, the free energy of reaction for the lithiation of silica is calculated for different products. The present first principles studies indicate that the formation of products is a highly exothermic and endergonic process in all cases. In the case of SiO2 lithiation, the free energy shows that the reaction to form Li2Si2O5 is highly exothermic, having the greatest probability of formation. The lithiation potentials and stability of different products are analyzed in the context of experimental results from the literature.