Lattice Energies for Some Ionic Compounds TABLE 8.1 Lattice Energy (kJ/mol) Compound Lattice Energy (kJ/mol) Compound 1030 LiF MgCl2 2526 LİCI 834 SrCl2 2127 Lil 730 NaF 910 MgO 3795 NaCl 3414 788 Cao NaBr 732 Sro 3217 Nal 682 KF 808 ScN 7547 КСІ 701 Kвг 671 CSCI 657 600 CsI
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
(a) Does the lattice energy of an ionic solid increase or decrease
(i) as the charges of the ions increase, (ii) as the sizes of the ions
increase? (b) Arrange the following substances not listed in
Table 8.1 according to their expected lattice energies, listing them
from lowest lattice energy to the highest: MgS, KI, GaN, LiBr.
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