Adsorption enthalpy integral

Integral adsorption enthalpies AH for the adsorption of poly(vinyl acetate), poly(n-butyl methacrylate), and polycaprolactone from carbon tetrachloride solutions on Aerosil 200 silica were measured by Korn and Killmann98), who used IR spectroscopy for the determination of p. The values obtained for the three polymers exhibited the same characteristic dependence on adsorbance as that observed for poly(ethylene glycol). If the enthalpy of polymer-solvent and polymer-polymer interactions is neglected, the net binding adsorption enthalpy AHp A can be calculated from... 

They are defined in complete analogy to the integral molar energy. The difference between the energy and the enthalpy of adsorption is usually small. If we treat the free gas as being ideal, the difference is AadU = AadHm1 + RT. At 25°C RT is only 2.4 kJ/mol. For this reason we do not need to worry too much about whether a heat of adsorption is the adsorption enthalpy or the internal adsorption energy, if we only want to estimate is. 

It is assumed that the binding energy of an adsorbed single molecule to the surface approximately equals its partial molar adsorption enthalpy at zero surface coverage. In the adsorbed state at zero surface coverage the individual variations of the entropy are partly but not completely suppressed. Hence, it is expected that this adsorption enthalpy is proportional to the standard sublimation enthalpy, which characterizes the volatility properties of pure solid phases as an integral value, ... 

Differential heat of adsorption or adsorption enthalpy Qiiff APiads J mof Defined from integral heat by Qditf ( Qjnt/ a)r,A... 

The aim of the present study was to quantify the changes in the integral adsorption enthalpies induced by the nature of the organic adsorbate. For that purpose, energy measurements were achieved for a wide panel of VOCs, representative of different... 

Figure 12.3 Integral adsorption enthalpy and corresponding immersion enthalpy as a function of pore size, as calculated by DFT for the filling of a sUt-shaped pore by a monoatomic fluid. (Adapted fi om [72].)...

The differential adsorption enthalpy given in kJ/kg adsorbed substance, is exchanged when the adsorbent load is increased from A to A -I- dA . The integral adsorption enthalpy Ah, given in kJ/kg adsorbent, is the evolution of heat if 1 kg adsorbent is loaded with adsorbate, starting from 0 to the final load A, ... 

Hence, from the experimental parameters and from the measured deposition temperature, the adsorption enthalpy can be determined directly. Again this simplification holds only for h 1 s [14, 15]. For experiments with very shortlived nuclides Eqs. (13, 21-23) have to be substituted into Eq. (2) and the resulting integral has to be solved numerically. 

Hence, for small or equal net adsorption enthalpies it can be expected that the adsorption enthalpy is proportional to the standard sublimation enthalpy, which characterizes the volatility properties of pure solid phases as an integral value ... 

Similarly, one may define the molar integral enthalpy of adsorption, SJt as... 

Table 4. Initial (A) and integral (B) enthalpy of adsorption of CO on polycrystalline evaporated metal films (kJ mol-1) (Ref.31))...

Molar entropy of an adsorbed layer perturbed by the solid surface Total enthalpy change for the immersion of an evacuated solid in a solution at a concentration at which monolayer adsorption occurs Heat of dilution of a solute from a solution Enthalpy change for the formation of an interface between an adsorbed mono-layer and solution Integral heat of adsorption of a monolayer of adsorbate vapor onto the solid surface... 

It is the energy difference between Na moles of gas adsorbed U"n (per mol) and the same amount free in the gas phase U. The next important quantities are the integral molar enthalpy of adsorption... 

In practice, most calorimetric experiments are carried out under constant pressure. By moving the piston down, the pressure in the cell is increased and the heat release is measured. In this case the heat exchanged is equal to the integral enthalpy of adsorption ... 

The present study was initiated to eliminate the difficulties inherent in the previous experiments. It consists of measurements of the integral enthalpies (via immersional heat measurements) and entropies (via adsorption isotherms) for ground and fractionated powders of fused quartz with a wide spectrum of specific surface areas. 

Probably the most significant comparisons which can be made are of values of properties determined from calorimetric measurements with values calculated from adsorption isotherms. Two general methods are available for the comparison of values of enthalpies determined from experiments of the two types. One involves two differentiations The change in the partial molal enthalpy, AH2, of X2, for Process 4, is determined from the differentiation with respect to n2/n1 of the integral heat of adsorption measured in a series of calorimetric experiments of the type represented by Equation 1. The values of the differential heats of adsorption (heats corresponding to the differential Process 4) are compared with values determined from the temperature variation of AG2/T for a series of values of n2/n in Process 4. This type of comparison has been made successfully by several groups of authors (3, 5, 10). 

The other method for the comparison of enthalpies depends upon the integration of Equation 5 as indicated by Equation 6 for each of a set of adsorption iso-... 

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