Cohesive Energy Ec

Because molecular interaction can occur as a result of dipole-dipole forces, London dispersion forces, and hydrogen bonding, the overall cohesion energy, Ec, can be considered to be made up of contributions from each type of interaction (represented as Ed, El, and Eh, respectively) ... 

Table 6.3. Comparison of some bnlk properties of silicon obtained with the LDA and the GGA equilibrinm lattice constant (a), bulk modulus (B) and cohesive energy (Ec). Bnlk modnli were obtained by fitting the Murnaghan equation of state [84] to the calculated total energy vs. volume curve. The experimental results (expt.) are those cited in [85]...

The values of/and AT in file above equation are def ndent on the density of cohesive energy Ec and on the stiffness parameter of an individual macromolecule a (43). The magnitude of/ tends towards an increase with tte increa% of o. For polymers with approximately equal a the rahie of/dian ani athicrdly to the density of col ave energy of the p<%mer Ec. In a general fivm/may be represented s... 

A property that is useful for interpreting intermolecular association in liquids is that known as the solubility parameter, S. When a liquid vaporizes, energy in the form of heat must be supplied to separate the molecules (to overcome the cohesion energy that holds the molecules together in the liquid state) and to perform the work done in expansion of the gas against atmospheric pressure. If the expansion work for one mole of gas is represented as RT (where R is 8.314 J mol-1 K-1) and the heat of vaporization is given by AHvap, it follows that the cohesion energy of a mole of the liquid, Ec, can be expressed by the equation... 

Thomas, E.R, and Eckert, C.A. (1984). Prediction of Limiting Activity Coefficients by a Modified Separation of Cohesive Energy Density Model and UNIFAC. I EC.Process Des.Dev., 23, 194-209. 

Figure 3.1 Size dependence of cohesive energies per atom (CE/n) of mercury clusters Hgn from calculations using a large-core EC-PP and CPP for Hg. Valence correlation is accounted for either within die hybrid model approach (HM) by a pair-potential adjusted for Hg2 or by pure-diffusion quantum Monte Carlo (PDMC) calculations (Wang etal 2000).

The work done as the vapor expands against the external (atmospheric) pressure is RT. The quantity Ec/V, where V is the molar volume, is called the cohesion energy density because it is the cohesion energy per unit volume. A basic thermodynamic relationship,... 

Although the terms cohesion energy density and internal pressure refer to the same characteristic of a liquid, they are not identical. The cohesion energy density (Ec/V) is equivalent to the energy of vaporization per mole of hquid and it is calculated in that way. The internal pressure, P , is given by... 

In polymers, it is usual to consider that Ec corresponds to 1 mole of CRU. Two materials can be compared through their cohesive energy density (CED), defined by CED = Ec/V, where V = M/p, is the molar volume of the CRU with molar mass M. CED is expressed in J m typical values for polymers range between 2 x 10 to 8 x 10 J m It is usual to convert these values into MPa (200 MPa < CED < 800 MPa). A practically important quantity is the solubility parameter, 8, defined by 8 = (CED) and expressed in or, better, in MPa. ... 

Botn-Haber cycle for NaCL The lattice energy Ufl is equal to the ionization energy of Na (/Na), less the electron affinity of Cl (.(Ici), plus the heat of disassodation of Cl (Eq) and the heat of vaporization of Na (Ev), less the cohesive energy of NaCl (Ec)- (Energy levels are drawn to scale.)... 

It was also proposed to consider conditionally a linear polymer as consisting of quasimolecules— the statistical segments as the kinetic units, because, as it was earlier found (150), in polymers there is no relation between Qp and the cohesion energy related to one mole of monomer units. Then, for these quasimolecules, the relation between Qp and Ec may be written as follows ... 

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