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 SiO2. 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 ΔG, ΔH, and ΔS. Predict the sign of ΔG. ΔG = 0 ΔG < 0 ΔG > 0 Predict the sign of ΔH. ΔH < 0 ΔH > 0 ΔH = 0 Predict the sign of ΔS. ΔS > 0 ΔS < 0 ΔS = 0

Answer 1

The sign of \Delta GΔG is negative.

The sign of \Delta HΔH is negative.

The sign of \Delta SΔS is negative.

Step-by-step explanation:

The water vapor is adsorbed on silica gel due to strong hydrophilicity of silica get towards the water.

The thermodynamic properties of adsorbate and adsorbent changes after adsorption. Silica gel is very porous and hydrophilic, thus, it absorbs the water from the shoe box.

The adsorption process occurs spontaneously, therefore Delta G < 0.

When adsorption occurs, bonds are formed between water molecules and SiO2, and the bond formation process is exothermic (heat is released).

Thus, Delta H < 0.

The water molecules become immobilized on the surface when adsorption occurs, thus, entropy/disorder decreases.

So, Delta S < 0.