Sublimation heat

The data required for computing various heat effects involving explosives and explosions are standard heats (also called enthalpies) of formation, heats of detonation (or explosion), heats of fusion, vaporization and/or sublimation, heat conductivity, and specific heat. 

Glass transition determinations Decomposition reaction Reaction kinetics Phase diagrams Dehydration reactions Solid-state reactions Heats of absorption Heats of reaction Heats of polymerization Heats of sublimation Heats of transition Catalysis... 

Supply the required sublimation heat to the product during the drying phase... 

In the solid state much has been done to define many hydrogen-bond configurations spatially, but little is known of their energies. This problem can perhaps best be tackled by the systematic study of sublimation heats some such studies are discussed. 

Some of the first systematic attempts to assess hydrogen, bond energies in the solid are due to Aihaba [16]. Typical of his studies of sublimation heats are the following simple set ... 

The figures in brackets are the increments resulting from the introduction of hydroxyl or carboxyl groups, For these simply related structures it would seem that the sublimation heats are derived addi-lively. Whilst this is not generally so, there are probably many other sets of structures for which this approximation applies. Without going into further examples here, it is obvious that much can be learnt of hydrogen bond contributions from lattice energies. 

SUBLIMATION (Heat of). The quantity of heat required at constant temperature (andpressure) to evaporate unitmass of a solid. In sublimation, the change is directly from solid to vapor, without appearance of the liquid phase,... 

Selected heat effect data (heats of formation, detonation, fusion, vaporization, and sublimation, heat conductivity coefficients and specific heats) for TNT and other common expls are given in Vol 7, H36-R to H46. Additional thermochemical data, up to about 1972, have been conveniently summarized (Ref 51). The data given below include some items which are more recent or less easily accessible... 

Iodine, ammonium chloride or dry ice can be used to demonstrate sublimation. Heat the solid ammonium chloride or iodine in a test-tube to show that it disappears from the bottom of the tube and condenses higher up the tube, where it is cooler. 

There is a AH for the process of sublimation, called the latent heat of sublimation (heat of sublimation). Sublimation is the conversion from the solid state to the gaseous physical state, skipping the liquid state. Elemental iodine, I2, and C02 are substances that sublime at 1 atm pressure. 

Following Van der Waals, we have leamt to think of the molecules as centres of forces and to consider these so-called Molecular Forces as the common cause for various phenomena The deviations of the gas equation from that of an ideal gas, which, as one knows, indicate the identity of the molecular forces in the liquid with those in the gaseous state the phenomena of capillarity and of adsorption the sublimation heat of molecular lattices certain effects of broadening of spectral lines, etc. It has already been possible roughly to determine these forces in a fairly consistent quantitative way, using their measurable effects as basis. 

In Table V. is also listed the lattice energy L (sublimation heat extrapolated to absolute zero after subtraction of the zero-point energy) for some molecule lattices, calculated on the basis of the same simplified formula (22). In all cases we have assumed closest packed structure, as this structure is at least approximately realised in the molecular lattices in question. The summation of (22) over the lattice gives... 

Tables 12.4 and 12.5 give a summary of average contributions to the molecular volume and surface, and to the (PE) at 7 A cutoff, for the most common atoms and groups. From these tables, total molecular volumes and surfaces can be obtained, and (PE) - and hence the sublimation energy - can be estimated, since (PE)7a s 0.85 Ai/s- Sublimation heats estimated from this correlation are too low for molecules with polar groups, having strong electrostatic interactions in the crystal or forming C-H...OorC-H...N hydrogen bonds (see 12.4.2.2).

The values of the evaporation and sublimation heats are usually quite close to each other, as well as the densities of solid substances and their melts, measured at the melting point. Consequently, the values of the surface energy at the liquid-vapor, aLV, and at the solid-vapor, osv, interfaces are nearly identical. Oppositely, the interfacial energy oSL at the interface between the solid phase and its melt is usually low oSL values normally do not exceed 1/10 of surface tension values of melt (note that the heats of melting are also on the order of -10% of those of evaporation). 

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