Enthalpy electron-gain

In some books, you will see electron affinity defined with an opposite-sign convention. Those values are actually the electron-gain enthalpies (Chapter 6). 

Write the electron gain enthalpy of Cl as the negative of the electron affinity (Fig. 1.54 or Appendix 2D). 

The lattice enthalpy, Aiatt//m, is the molar enthalpy change accompanying the formation of a gas of ions from the solid. Since the reaction involves lattice disruption the lattice enthalpy is always large and positive. Aatom//m and Adiss//m are the enthalpies of atomization (or sublimation) of the solid, M(s), and the enthalpy of dissociation (or atomization) of the gaseous element, X2(g). The enthalpy of ionization is termed electron gain enthalpy, Aeg//m, for the anion and ionization enthalpy, Ajon//m, for the cation. 

Figure 7.4 Thermodynamic data needed in evaluation of the enthalpy of formation of MX(s). (a) Lattice enthalpy of sodium halides (b) lattice enthalpy of alkali iodides (c) electron gain and dissociation enthalpies of halides (d) ionization and atomization enthalpies of alkali metals.

Larger differences are observed when comparing the enthalpy of formation of the different halides of a given alkali metal. The enthalpy of formation of gaseous halide ions is exothermic since the exothermic electron gain enthalpy in absolute value is larger than the endothermic dissociation enthalpy. Furthermore, the enthalpy of formation of gaseous halide ions becomes less favourable with... 

It is generally accepted that the electron affinity is positive (electron gain is exothermic) if the energy release accompanies the electron attachment. The standard enthalpy of electron gain, AegTP, at a temperature T, is related to the electron affinity,... 

The standard enthalpy of electron gain of a molecular entity X is opposite to the standard ionization enthalpy of its negative ion, Aion TP(X ). 

Electron Gain Energy, Electron Gain Enthalpy and Electron Affinity... 

Energy transfer 144 Enthalpy 72, 79 electron gain 29, 30 hydration 73 ionization 22, 33 lattice 51, 101 vaporization 44 Entropy 72, 79 Equilibrium constant 72, 74... 

E3.24 The most important terms will involve the lattice enthalpies for the di- and the trivalent ions. Also, the bond dissociation energy and third electron gain enthalpy for nitrogen (Nj) will be large. See Section 3.11 for more details. 

Enthalpy of electron gain (-AHJg is called electron affinity) AH g one mole of anions being formed all species in the gas phase F(g) H- e- F-(g)... 

We use the convention that Eea > 0 signifies a positive affinity for the added electron. Distinguish the electron affinity from the electron-gain enthalpy, which is negative for such an exothermic process (that is, has the opposite sign to the electron affinity, and differs very slightly in value). 

Typical elements in Groups V. VI and VII would be expected to achieve a noble gas configuration more easily by gaining electrons rather than losing them. Electron affinity is a measure of the energy change when an atom accepts an extra electron. It is difficult to measure directly and this has only been achieved in a few cases more often it is obtained from enthalpy cycle calculations (p. 74). 

If defects are not independent but interact between each other, the total enthalpy of the lattice is affected by this interaction. AHi ter takes care of the gain or loss of total enthalpy due to the interaction fields. AHi ter is dependent on both N and N (where N is the number of cationic compensating charges, usually related through stoichiometry to N), since both lattice defects and electronic disorder are electrical charges with respect to the lattice. 

The common oxidation states are -3, +3 and +5, but the simple ions As3-, As3+ and As5+ are not known. The krypton electronic structure could be attained by gain of three electrons, but there is a high energy requirement. Equally, the loss of five valence electrons to form As5+ is unrealizable because of the high ionization enthalpy. 

The example illustrates that enthalpy can be gained when nonpolar bonds, as commonly encountered in organic molecules, are broken and polar bonds, such as those in carbon dioxide and water, are formed. Reactions which involve the transfer of electrons between different chemical species are generally referred to as redox reactions. Such reactions form the basis for the energy production of all organisms. From this point of view we can consider organic compounds as energy sources. 

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