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Explain bond haber cycle with suitable example.

Answer» Born Haber cycle is a simplified method developed by Max Born and Fritz Haber in 1919 to correlate the lattice energies of ionic solids to other thermodynamic data. Lattice enthalpy or lattice energy is defined as enthalpy change which occurs when one mole of ionic solid is formed by close packing of constituent ions in gaseous state. Or it may be defined as energy released when one mole of ionic solid dissociates into its gaseous state. For example, the formation of sodium chloride from sodium and chloride ion involves 788 kj/mol of energy and dissociation of sodium chloride into it constituent ions requires same amount of energy.NaCl(s) → Na+(g) + Cl- (g) ΔL H°= 788 kj/molNa+(g) + Cl-(g) → NaCl(s) ΔL H° = -788 kj/molWhen oppositely charged ions interact to form ionic solid, a large amount of energy is released and dissociation of crystal also require a lot of energy which makes melting point and boiling points of crystal very high. Born Haber cycle is used to determine this lattice energy by using other energy values like ionization energy, electron affinity, dissociation energy, sublimation energy and heat of formation. Ionization Energy: It is the energy required to remove an electron from a neutral gaseous atom or an ion.Electron Affinity: It is the energy released when an electron is added to an isolated neutral gaseous atom or an ion.Dissociation energy: The energy required to dissociate a compound is called as dissociation energy. Dissociation of a compound is always an endothermic process and requires an input of energy.Sublimation energy: The energy required to change the phase from solid to gas, by passing the liquid phase is called as sublimation energy.Heat of formation: The energy change during the formation of a compound from its elements is known as heat of formation.Born Haber cycle is based on Hess law which states that the standard enthalpy change of reactions is the sum of algebraic sum of the standard enthalpies of reactions into which the overall reaction may be split or divided.For example, the formation of C from A and B can take place in two ways. Both ways involve same initial and final states, but one is single step and other one is multi-step reaction which involves intermediates, D and E. Both ways has an enthalpy change of 160 kJ.<br>The Born–Haber cycle is an approach to analyze reaction energies. It was named after the two German scientists Max Born and Fritz Haber, who developed it in 1919.[1][2][3] It was also independently formulated by Kasimir Fajans.[4] The cycle is concerned with the formation of an ionic compound from the reaction of a metal (often a Group I or Group II element) with a halogen or other non-metallic element such as oxygen.Born–Haber cycles are used primarily as a means of calculating lattice energy (or more precisely enthalpy[note 1]), which cannot otherwise be measured directly. The lattice enthalpy is the enthalpy change involved in the formation of an ionic compound from gaseous ions (an exothermic process), or sometimes defined as the energy to break the ionic compound into gaseous ions (an endothermic process). A Born–Haber cycle applies Hess\'s law to calculate the lattice enthalpy by comparing the standard enthalpy change of formation of the ionic compound (from the elements) to the enthalpy required to make gaseous ions from the elements.This latter calculation is complex. To make gaseous ions from elements it is necessary to atomise the elements (turn each into gaseous atoms) and then to ionise the atoms. If the element is normally a molecule then we first have to consider its bond dissociation enthalpy. The energy required to remove one or more electrons to make a cation is a sum of successive ionization energies; for example, the energy needed to form Mg2+ is the ionization energy required to remove the first electron from Mg, plus the ionization energy required to remove the second electron from Mg+. Electron affinity is defined as the amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.The Born–Haber cycle applies only to fully ionic solids such as certain alkali halides. Most compounds include covalent and ionic contributions to chemical bonding and to the lattice energy, which is represented by an extended Born-Haber thermodynamic cycle.[5] The extended Born–Haber cycle can be used to estimate the polarity and the atomic charges of polar compounds.


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