Collectively, these data and interpretations show that H 2 O molecules coalesce into structures, whose shape and properties depend strongly on the topology of the surrounding pore and to a lesser degree on the [(SiOH) x ]. As the characteristic dimensions of the pores decrease, the H 2 O solvent structures lose the added stability conferred by forming HB with other H 2 O in more than one dimension and become motion among H 2 O molecules becomes increasingly correlated. Therefore, the enthalpic costs and entropic gains associated with breaking each HB depend on zeolite topology. These relationships between the enthalpy and entropy of creating and forming HBs with H 2 O molecules carries catalytic consequences that appear as differences in turnover rates and the stability of surface intermediates at solid-liquid interfaces, as we demonstrate below.