| 单词 | Born-Haber cycle |
| 释义 | Born-Haber cycle A cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction M+(g) + X-(g) → M+X-(s) ΔHL The standard enthalpy of formation of the ionic solid is the enthalpy of the reactionM(s) + ½X2(g) → M+X-(s) ΔHf The cycle involves equating this enthalpy (which can be measured) to the sum of the enthalpies of a number of steps proceeding from the elements to the ionic solid. The steps are:(1) Atomization of the metal: M(s) → M(s) ΔH1 (2) Atomization of the nonmetal: ½X2(g) → X(g) ΔH2 (3) Ionization of the metal: M(g) → M+(g) + e ΔH3 This is obtained from the ionization potential.(4) Ionization of the nonmetal: X(g) + e → X-(g) ΔH4 This is the electron affinity.(5) Formation of the ionic solids: M+(g) + X-(g) → M+X-(s) ΔHL Equating the enthalpies gives:ΔHf + ΔH1 + ΔH2 + ΔH3 + ΔH4 + ΔHL from which ΔHL can be found. It is named after Max Born and the German chemist Fritz Haber (1868–1934) |
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