Enthalpy of absorption

The enthalpy of absorption of 1- and 2-nitropropane on breathing mask cartridges made with carbon is such that the decomposition of the nitrated derivative can cause its ignition. This accident is aggravated when the cartridge also contains metal oxides such as copper (II) oxide or manganese dioxide. 

As shown in Fig. 2.43b, the enthalpy of absorption and desorption calculated from the Van t Hoff plots using the mid-plateau pressures of PCT curves in Fig. 2.43a, which are listed in Table 2.18, is equal to -72 and 83 kJ/mol, respectively. The value of entropy is 138 and 151 J/mol K for absorption and desorption, respectively. The enthalpy value for absorption is very close to the values found in the literature for MgHj as discussed in Sect. 2.1.2 and 2.1.3. Surprisingly, however, the enthalpy of desorption at 83 kJ/mol is much greater than the former and also greater than the enthalpy of desorption of the as-received and activated MgH as shown in Fig. 2.11. The coefficients of fit are excellent and give good credibility to the obtained values. 

Leung, P.C., Zorrilla, C., Pulgjaner, L., and Recasens, F. Solubilities and enthalpies of absorption of isobutene into ferf-butyl alcohol-water mixtures, J. Chem. Eng. Data, 32(2) 169-171, 1987. 

Figure 3.4-2 Enthalpy of absorption for water vapor in various solvents at 25 °C.

The enthalpies decrease in magnitude in the order of decreasing solubihty. Interestingly, O2 and Ar exhibit positive enthalpies of absorption, indicating that there are no measurable attractive forces and that their dissolution in the IL is entirely entropicaUy driven. Thus, gas solubilities are a useful probe of interactions in ILs. 

The above stated hypothesis is supported by the existence of a high positive enthalpy of absorption, AH°b, in the studied material (see Table 5.1 and Figure 5.25), which is consistent with the increase of electrons with temperature in the conduction band [32], The value measured for the enthalpy of absorption, AH°b, for this material uses the following expression (see Figure 5.25)... 

This gives A// ), = (3.6 0.5) eV, and the linear regression coefficient, r2 = 0.93. It is necessary at this point to affirm that positive values for the enthalpy of absorption are possible in metals [7] and oxides [53],... 

The initial storage material, Ca2NH, was synthesised by dehydrogenation of a 1 1 mixture of Ca3N2 -1- CaH2 at 550 °C. Theoretically, 2.1 wt% of H can be stored in the nitride hydride and experimentally the maximum reversible capacity at 550 °C was close to this (c. 1.9 wt%). The calculated standard enthalpy of absorption for Ca2NH = -88.7kJmol ) is somewhat... 

Finally, since the absorption of hydrogen is thermodynamically unfavourable with respect to adsorption (enthalpy of adsorption at low coverage, — lOOkJmor enthalpy of absorption at infinite dilution — 20kJmor ), and yet absorption occurs under conditions where adsorption is inhibited, it must be concluded that adsorption is suppressed by a purely surface effect. 

C. Mathonat, V. Majer, A.E. Mather, J.-P.E. GroUer, Enthalpies of absorption and solubiUty of CO2 in aqueous solutions of methyldiethanolamine. Ruid Phase EquiUb. 140(1-2), 171-182 (1997)... 

I. Kim, K.A. Hoff, E.T. Hessen, T. Haug-Warberg, H.F. Svendsen, Enthalpy of absorption of CO2 with alkanolamine solutions predicted from reaction equilibrium constants. Chem. Eng. Sci. 64(9), 2027-2038 (2009)... 

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