Question

definition of born- haber cycle

Answer 1

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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 1916. The cycle is concerned with the formation of an ionic compound from the reaction of a metal (often a Group Ior 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 enthalpychange 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 formationof 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 (see also bond energy). 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.[1] The extended Born–Haber cycle can be used to estimate the polarity and the atomic charges of polar compounds.

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Answer 2

Born-haber Cycle


Born-Haber Cycle is a methodology to analyze the reaction energy, which was introduced by German scientist Born and Firtz Haber. It explains about the formation of ionic compounds,

There are various processes involved in Born-Haber Cycle.

1. Electron affinity

2. Ionization energy

3. Sublimation energy

4. Heat of formation

5. Dissociation energy

Process 1: Electron affinity

Energy released when an electron is added to the neutral atom. The trend of electron affinity in the periodic table; electron affinity increases along the period (from left to right in the periodic table) and electron affinity decreases down the group.

Process 2: Ionization energy

Ionization energy is the energy required to remove an electron form a neutral atom or form an ion. In this process, energy is required to remove an electron from an atom; hence, the value of ionization energy will always be positive values. The trend of ionization energy in the periodic table is that ionization energy decreases from the top to bottom in the group and increases from left to right in the period.

Process 3: Sublimation Energy

It is the energy required to change the phase of the reactants from solid to gas. Since, energy is utilized for the conversion of one phase to another, sublimation energy is positive.

Process 4: Heat of formation

It is the energy change when a compound is formed from elements. The energy may be positive or negative since it depends on the interaction of the atoms in the molecule.

Process 5: Dissociation energy

It is the energy required to break a chemical bond. It is an endothermic process since it needs energy.