Vapor pressure molecular interactions underlying

When a gas comes in contact with a solid surface, under suitable conditions of temperature and pressure, the concentration of the gas (the adsorbate) is always found to be greater near the surface (the adsorbent) than in the bulk of the gas phase. This process is known as adsorption. In all solids, the surface atoms are influenced by unbalanced attractive forces normal to the surface plane adsorption of gas molecules at the interface partially restores the balance of forces. Adsorption is spontaneous and is accompanied by a decrease in the free energy of the system. In the gas phase the adsorbate has three degrees of freedom in the adsorbed phase it has only two. This decrease in entropy means that the adsorption process is always exothermic. Adsorption may be either physical or chemical in nature. In the former, the process is dominated by molecular interaction forces, e.g., van der Waals and dispersion forces. The formation of the physically adsorbed layer is analogous to the condensation of a vapor into a liquid in fret, the heat of adsorption for this process is similar to that of liquefoction. 

A number of important characteristics of polymers, such as molecular weight, chain length, branching, and chain stiffness, can be explored when the individual molecules are separated froni each other. Such studies therefore employ dilute solutions of polymers. However, the dissolution of a polymer also brings with it many new problems. For a correct interpretation of the behavior of polymer solutions it is essential to understand the thermodynamics of polymer-solvent interaction. We will therefore explore some of the basic underlying thermodynamic principles of polymer solutions in this chapter. A major part of the chapter will be concerned with methods of studying polymer solutions that deal with equilibria and can be fully described by thermodynamic relations. These include vapor pressure, osmotic pressure, and phase separation in polymer-solvent systems. 

The following table presents the solubilities of several gases in water at 25 "C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH4(g) under standard conditions of temperature and pressure is contained in 4.0 L of a saturated solution at 25 °C (b) Explain the variation in solubility among the hydrocarbons listed (the first three compounds), based on their molecular structures and inter-molecular forces, (c) Compare the solubilities of O2, N2, and NO, and account for the variations based on molecular structures and intermolecular forces, (d) Account for the much larger values observed for H2S and SO2 as compared with the other gases listed, (e) Find several pairs of substances with the same or nearly the same molecular masses (for example, C2H4 and N2), and use intermolecular interactions to explain the differences in their solubilities. 

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