The small bags of silica gel you often see in a new shoe box are placed there to

ID: 1068404 • Letter: T

Question

The small bags of silica gel you often see in a new shoe box are placed there to control humidity. Despite its name, silica gel is a solid. It is a chemically inert, highly porous, amorphous form of SiO_2. Water vapor readily adsorbs onto the surface of silica gel, so it acts as a desiccant. Despite not knowing mechanistic details of the adsorption of water onto silica gel, from the information provided, you should be able to make an educated guess about the thermodynamic characteristics of the process. Predict the signs of Delta G, Delta H, and Delta S.

Explanation / Answer

HEre.. silica is in solid form and it's adsorbing water molecules so entropy change in this rection would be positive.

Because liquid has more entropy then solid.

enthalpy in this would be decreses.because adsorption of water on silica grnerates microdroplets.and reduction in enthalpy of fusion can be considered size dependent.

free energy also decreases.

The effect of confinement on the solid–liquid phase transitions of water was studied by using DSC and FT-IR measurements. Enthalpy changes upon melting of frozen water in MCM-41 and SBA-15 were determined as a function of pore size and found to decrease with decreasing pore size. The melting point also decreased almost monotonically with a decrease in pore size. Analysis of the Gibbs–Thomson relation on the basis of the thermodynamic data showed that there were two stages of interfacial free energy change after the constant region, i.e., below a pore size of 6.0 nm: a gradual decrease down to 3.4 nm and another decrease after a small jump upward. This fact demonstrates that the simple Gibbs–Thomson relation, i.e., a linear relation between the melting point change and the inverse pore size, is limited to the range not far from the melting point of bulk water. FT-IR measurements suggest that the decrease in enthalpy change and interfacial free energy change with decreasing pore size reflect the similarity of the structures of both liquid and solid phases of water in smaller pores at lower temperatures.

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The small bags of silica gel you often see in a new shoe box are placed there to

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The small bags of silica gel you often see in a new shoe box are placed there to

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