Solids lattice energy

The trinitrotoluene isomers follow the same trends, invoking dinitro steric interactions and favorable solid lattice energies, as the dinitrotoluenes. 

In discussing the energetics of the formation of solid lithium fluoride, we emphasized the importance of lattice energy in contributing to the stability of the ionic solid. Lattice energy can be represented by a modified form of Coulomb s law,... 

Liquids and solids from the kinetic-molecular viewpoint Phase diagrams of one-component systems Changes of state, including critical points and triple points Structure of solids lattice energies... 

To compare bond strengths in ionic compounds, chemists compare the amounts of energy released when separated ions in a gas come together to form a crystalline solid. Lattice energy is the energy released when one mole of an ionic crystalline compound is formed from gaseous ions. 

Born-Haber cycle A thermodynamic cycle derived by application of Hess s law. Commonly used to calculate lattice energies of ionic solids and average bond energies of covalent compounds. E.g. NaCl ... 

Dislocation theory as a portion of the subject of solid-state physics is somewhat beyond the scope of this book, but it is desirable to examine the subject briefly in terms of its implications in surface chemistry. Perhaps the most elementary type of defect is that of an extra or interstitial atom—Frenkel defect [110]—or a missing atom or vacancy—Schottky defect [111]. Such point defects play an important role in the treatment of diffusion and electrical conductivities in solids and the solubility of a salt in the host lattice of another or different valence type [112]. Point defects have a thermodynamic basis for their existence in terms of the energy and entropy of their formation, the situation is similar to the formation of isolated holes and erratic atoms on a surface. Dislocations, on the other hand, may be viewed as an organized concentration of point defects they are lattice defects and play an important role in the mechanism of the plastic deformation of solids. Lattice defects or dislocations are not thermodynamic in the sense of the point defects their formation is intimately connected with the mechanism of nucleation and crystal growth (see Section IX-4), and they constitute an important source of surface imperfection. 

The overall lattice energies of ionic solids, as treated by the Born-Eande or Kaputin-sldi equations, thus depends on (i) the product of the net ion charges, (ii) ion-ion separation, and (iii) pacldng efficiency of the ions (reflected in the Madelung constant, M, in the Coulombic energy term). Thus, low-melting salts should be most... 

Equilibrium in any reaction is determined by a compromise between tendency toward minimum energy f golf balls roll downhill ) and tendency toward maximum randomness. Reaction (29) and reaction (30) both involve increase in randomness since the regular solid lattice dissolves or melts to become part of a disordered liquid state. Both reactions produce ions. But reaction (29) proceeds readily at 25°Q whereas reaction (30) does not... 

EXAMPLE 2.2 Sample exercise Estimating the relative lattice energies of solids... 

The lattice enthalpy can be identified with the heat required to vaporize the solid at constant pressure. The greater the lattice enthalpy, the greater is the heat required. Heat equal to the lattice enthalpy is released when the solid forms from gaseous ions. In Section 2.4 we calculated the lattice energy and discussed how it depended on the attractions between the ions. The lattice enthalpy differs from the lattice energy by only a few kilojoules per mole and can be interpreted in a similar way. 

In Fig. 8-13 are plotted lattice energies for MCI2 species. The metal ions are high-spin and lie in octahedral sites in the lattice. The double-hump form of the curve is obviously similar to that for the hydration energies we have just discussed. The reasons for the observed trend in lattice energy are virtually identical to those described for hydration energies. In one system, a metal(ii) ion is octahedrally coordinated by six water molecules within a liquid medium in the other, a metal(ii) ion is octahedrally coordinated by six chlorine atoms within a solid lattice. 

Na (g) + Cl (g) NaCK. ) A -calculated - - 769 kJ/mol This Is the energy released when the solid forms from separated gaseous ions. The reverse process, in which an ionic solid decomposes into gaseous ions, is termed the lattice energy (LE) and is a positive quantity ... 

The lattice energies of these solids are large enough to make the overall reaction energy-releasing despite the large positive second electron affinity of the anions. In addition, three-dimensional arrays of surrounding cations stabilize the - 2 anions in these solids. 

The solid-vapor boundary line extrapolates to P = 0 and T = 0. This is a consequence of the direct link between temperature and molecular energy. At T = 0 K, molecules have minimum energy, so they cannot escape from the solid lattice. At 0 K, the vapor pressure of every substance would be 0 atm. 

The possibility of measuring the Volta potential in the system metal-solid-state electrolyte and using the data obtained to determine ionic components of the free lattice energy has been shown in our papers. Earlier, Copeland and Seifert measured the Volta potential between Ag and solid AgNOj in the temperature range between 190 and 280 °C. They investigated the potential jump during the phase transition from solid to liquid salt. 

In the case of ionic solid substances, an important quantity is the free lattice energy AGS, i.e., the energy liberated when one type of crystalline substance is formed from its ionic constituents in the gas phase. This definition implies that this magnitude for a simple 1 1 solid electrolyte is a sum of the real potentials of cation and anion ... 

The energy required to overcome lattice energies and intermolecular or interionic attractions for the dissolution of a solid in a liquid comes from the formation of new attractions between solute and solvent. 

Conventional electrolytes applied in electrochemical devices are based on molecular liquids as solvents and salts as sources of ions. There are a large number of molecular systems, both pure and mixed, characterized by various chemical and physical properties, which are the liquids at room temperatures. This is the reason why they dominate both in laboratory and industrial scale. In such a case, solid salt is reacted with a molecular solvent and if the energy liberated during the reaction exceeds the lattice energy of the salt, the solid is liquified chemically below its melting point, and forms the solution. Water may serve as an example of the cheapest and most widely used molecular solvent. 

---