subject: Born Haber Cycle Examples [print this page] Introduction to Born Haber cycle: Introduction to Born Haber cycle:
The Born Haber cycle examples is the direct experimental determination of lattice energies. These are determined indirectly with the help of a thermo-chemical cycle process known as Born Haber cycle. We would illustrate by taking into consideration the determination of the lattice energy of Na Cl.
Experimental determination of Lattice Energy:
The various steps involved in the formation of NaCl (s) in crystalline state by Born Haber Cycle examples are as follows:
Conversion of Metallic Sodium into Gaseous Sodium Atoms. The energy required for the conversion of one mole of metallic sodium into gaseous sodium atoms is called sublimation energy. It is denominated by S.
Na (s) + S --> Na (g); S= it is denoted as energy of sublimation.
Dissociation of Gaseous Chlorine Molecules into Gaseous Chlorine Atoms:
This step involves the dissociation of gaseous chlorine molecules into gaseous chlorine atoms. The amount of energy required to dissociate one mole of gaseous chlorine molecules into gaseous atoms is called dissociation energy. It is denoted by D.
Cl2 (g) + D -->2Cl (g); D= Dissociation energy
Evidently, the energy required to produce one mole of gaseous chlorine atoms would be D/2.
Conversion of Gaseous Sodium Atoms into Sodium Ions:
The amount of energy required to convert one mole of gaseous sodium atoms into sodium ions in the gaseous state is called ionization energy. This may be denoted by IE.
Na (g) + IE-->Na+ (g) + e-;IE = ionization energy.
Conversion of Gaseous Chlorine Atoms into Chloride Ions:
The amount of energy released when one mole of gaseous chlorine atoms are converted into chloride ions in the gaseous state is called electron affinity. It is denoted by EA.
Cl (g) + e- --> Cl- (g) + EA;
Combination of Gaseous Ions to form a solid crystal:
This step involves the combination of gaseous Na+ and Cl- ions to give one mole of sodium chloride crystal. The amount of energy released when one mole of solid crystalline compound is formed from gaseous ions of opposite charges is called Lattice energy. It is denoted by U.
Na+ (g) + Cl- (g)--> NaCl (s) + U; U= Lattice energy
The overall change may be denoted as
Na (s) + Cl2 (g)--> NaCl (s);
The enthalpy change or this reaction is called enthalpy of formation of sodium chloride and may be denoted as ?Hf.
According to Hesss law, the enthalpy of formation of sodium chloride should be the same irrespective of the fact whether it takes place directly in one step or through a number of steps, as illustrated below. Hence,
?Hf = S + (1/2) D + IE + EA + U
Using positive sign for energy absorbed and negative sign for energy released. These are the some of the Born Haber cycle examples.
