Ionic solids tend to be an extremely stable compounds. The enthalpies of formation of the ionic molecules cannot alone account for this stability. This compounds have second stability as result of the lattice energy of the solid structure. However, lattice power cannot be straight measured. The Born-Haber cycle permits us to understand and determine the lattice energies the ionic solids.

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This module will introduce the idea the lattice energy, as well as one process that enables us to calculate it: the Born-Haber Cycle. In stimulate to use the Born-Haber Cycle, there space several ideas that we must know first.

Lattice Energy

Lattice power is a form of potential power that may be defined in two ways. In one definition, the lattice energy is the energy required to rest apart an ionic solid and convert its component atoms into gaseous ions. This an interpretation causes the worth for the lattice power to always be positive, since this will always be an endothermic reaction. The other definition says the lattice energy is the turning back process, an interpretation it is the energy released as soon as gaseous ions bind to type an ionic solid. As implied in the definition, this procedure will constantly be exothermic, and thus the value for lattice power will it is in negative. That values space usually expressed with the systems kJ/mol.

Lattice power is supplied to describe the stability of ionic solids. Some could expect such an ordered framework to be less stable due to the fact that the entropy the the system would be low. However, the crystalline structure allows each ion to connect with many oppositely charge ions, which causes a very favorable change in the enthalpy the the system. A many of power is released as the oppositely charged ion interact. The is this that reasons ionic solids to have actually such high melting and also boiling points. Some need such high temperatures that they decompose prior to they deserve to reach a melting and/or cook point.

Born-Haber Cycle

There are several important principle to understand before the Born-Haber Cycle have the right to be used to recognize the lattice power of one ionic solid; ionization energy, electron affinity, dissociation energy, sublimation energy, warm of formation, and Hess"s Law.

Dissociation energy is the energy required to break apart a compound. The dissociation of a link is always an endothermic process, an interpretation it will constantly require an input of energy. Therefore, the change in energy is constantly positive. The size of the dissociation power depends on the electronegativity that the atoms involved. The warmth of formation is the adjust in energy when forming a compound from the elements. This might be confident or negative, depending upon the atoms involved and how castle interact.

Using the Born-Haber Cycle

The values offered in the Born-Haber Cycle space all predetermined alters in enthalpy because that the processes described in the ar above. Hess" Law enables us to add or subtract this values, which permits us to determine the lattice energy.


Step 5

Now the metal and nonmetal will certainly be an unified to kind the ionic solid. This will reason a relax of energy, which is called the lattice energy. The worth for the lattice energy is the difference in between the value from step 1 and also the value from step 4.


The diagram below is one more representation that the Born-Haber Cycle.

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Lattice energy: The distinction in energy in between the expected speculative value because that the energy of the ionic solid and also the actual value observed. Much more specifically, this is the energy gap between the power of the different gaseous ions and also the power of the ionic solid. Ionization energy: The energy readjust associated with the removed of an electron from a neutral atom or ion. Electron affinity: The relax of energy linked with the addition of one electron come a neutral atom or ion. Hess" law states the the all at once energy that a reaction might be established by breaking under the process into number of steps, then including together the alters in power of every step. Lattice Energy= <-436.68-89-(0.5*158)-418.8-(-328)> kJ/mol= -695.48 kJ/mol Lattice Energy= <-641.8-146-243-(737.7+1450.6)-(2*-349)> kJ/mol= -2521.1 kJ/mol MgO. It has ions with the largest charge. AlCl3. According to the routine trends, together the radius that the ion increases, lattice energy decreases.