Entropies aluminosilicate

The initial entropy of cumene adsorption on a commercial aluminosilicate was measured to be about —750JmoP K , whereas the gas-phase entropy of cumene at 298 K is 389 J moP K (709). This seemingly inconsistent result appears to be caused by the dissociative adsorption of cumene at low coverages on this catalyst. In this case, the measured heat corresponds to a combination of heats of adsorption and reaction. Higher coverages produced lower, nearly constant heats and entropies of adsorption. These entropies correspond to the loss of between two and three degrees of translational freedom. The adsorption of benzene on these samples did not show abnormally... 

These data suggest very negative entropies of hydration for H2O molecules surrounding cations sandwiched between aluminosilicate layers. If this structuring of water is a general phenomenon, it may have significant implications for diffusion and reactivity at layer and nanoparticle surfaces. 

Clay particles occur abundantly in the soil. They are mostly colloidal aluminosilicates. To learn how their extensive surfaces react with water, we have studied the following properties of water associated with montmorillonite and other clay minerals threshold gradient [1], thermal expansibility [2, 3], isothermal compressibility [4], frequency of O—H stretching [5, 6], molar absorptivity [7], freezing point depression [8, 9] specific volume [10], specific heat capacity [11], heat of compression [12], viscosity [13], and free energy, enthalpy and entropy [6,14,15]. Not all of these properties will discussed here. Instead, we will discuss only a few of them to illustrate the kind of results obtained. 

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