Enthalpy hydrogen formation

Shao et al. [62] used Mg and Co nanoparticles with the size of 200-300 and 5-60 nm, respectively, for the synthesis of nanoparticulate Mg CoH (particle size 50-300 nm range) by pressing 2 1 powder mixtures of Mg and Co into pellets and then very complicated sintering under a hydrogen scheme. They observed the formation of two hydride phases Mg CoH and MgjCoH. From the Van t Hoff plot the formation enthalpy and enttopy were estimated as -82.3 kJ/molH and -138.8 kJ/molH K for Mg CoH, and -73.2 kJ/molH and -123.0 kJ/molH K for MgjCoHj, respectively. 

In References 32 and 33 we find the liquid phase enthalpies of formation of the methyl and allyl esters of the OO-fert-butyl peroxyfumaric and peroxysuccinic acids. The difference between the enthalpies of formation of each fumarate and succinate pair of peresters is the enthalpy of hydrogenation. The enthalpy of hydrogenation to the succinate of the methyl fumarate is —131.4 3.6 kJmol", and of the allyl fumarate is... 

Fig. 5.26 The principle behind the ab initio calculation of heat of formation (enthalpy of formation) by the atomization method. Methanol is (conceptually) atomized at 0 K into carbon, hydrogen and oxygen atoms the elements in their standard states are also used to make these atoms, and to make methanol. The heat of formation of methanol at 0 K, A// (CH3OH), follows from equating the energy needed to generate the atoms via methanol (A//g(CH3OH) + A/f (CH3OH)) to that needed to make them directly from the elements in their standard states. The diagram is not meant to imply that methanol necessarily lies above its elements in enthalpy...

Formation enthalpy of hydrogen of required amount for hydrocarbon regeneration... 

AHa, will be solvent-dependent unless IA//3I = IA Hi + AH2, where A Hi and A H2 are the heats of solvation of the electron donor and the hydrogen compound, respectively, and AH3 is the heat of solvation of the complex. The enthalpy of the formation of the adduct in the gas phase, which would give the actual strength of the hydrogen bond, will be different from that in solution unless the solvation energies cancel. In many cases, this is questionable because of the electron donor properties of the solvent. There is no doubt that many of the hydrogen bond enthalpies reported in the literature may be in error because of this. Moreover, it has been shown that the extent of self-association of... 

The reaction yielded a reversible hydrogen capacity of 6.5 wt%. If the imide were subsequently decomposed, the overall hydrogen capacity of the amide-hydride pair would be 11.5 wt%. As with other systems, however, this total capacity has not been achieved reversibly. Furthermore, the formation enthalpy and hydrogen transport kinetics of this system require high temperatures ( 350°C) for hydrogen release at reasonable rates. Some improvement in hydrogen release kinetics was achieved by incorporating Ti catalysts. ... 

Both the bridge and the cyclopropane ring are broken on hydrogenation. The enthalpy of formation given (see original paper) was calculated on the basis of methylcycloheptane as the reaction product. 

---