(a) Give a definition of lattice energy. Does your definition mean that the associated enthalpy of reaction will be positive or negative? 

(b) Use the Born–Lande´ equation to calculate a value for the lattice energy of KBr, for which r₀ = 328 pm. KBr adopts an NaCl structure; other data may be found in Tables 6.3 and 6.4.

Table 6.3 

Values of the Born exponent, n, given for an ionic compound MX in terms of the electronic configuration of the ions [M⁺][X‾]. The value of n for an ionic compound is determined by averaging the component values, e.g. for MgO, n = 7; for LiCl

Table 6.4

Transcribed Image Text:

5+9 2 n=" 7. Electronic configuration of the ions in an ionic compound MX [He][He] [Ne][Ne] [Ar][Ar], or [3d¹][Ar] [Kr][Kr] or [4d¹][Kr] [Xe][Xe] or [5d'][Xe] Examples of ions n (no units) H™, Lit 5 2+ 7 F, 0², Na, Mg²+ CI, S², K+, Ca²+, Cut 9 10 12 Br, Rb+, Sr²+, Ag+ I,Cs*, Ba2+, Au*