Chemical Energetics - More Energy Cycles

In this post, I will be sharing with you how to construct (i) Born Haber Cycle and (ii) Energy Level Diagram. In principle, both are considered energy cycles but these cycles are usually used to calculate enthalpy change of formation of the ionic compound. These cycle also can help to calculate lattice energy, should the value of enthalpy change of formation of the ionic compound can be obtained. (You can read about how to construct a generic energy cycle over here.)

Like in the earlier post, the state symbols of all the substances have to be shown.

My example which I will use to illustrate how to draw the Born Haber cycle is the standard enthalpy change of formation of CaF₂. As standard conditions are employed, the enthalpy change of atomisation of Ca and F are also in standard conditions. (You would expect enthalpy change of atomisation of solid F₂ to be more endothermic than that of gaseous F₂.)

It is interesting to note that it is quite impossible to obtain a standard condition for ionisation energy (I.E.) and electron affinity (E.A); we shall however assume that these will be constant at all temperatures.

(i) Born Haber Cycle:

In addition, I will use the standard enthalpy change of formation of CaO to demonstrate how to construct energy level diagram. The considerations are the same as earlier mentioned; with enthalpy change of atomisation of Ca and O to be at standard conditions.

(ii) Energy Level Diagram:



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Article written by Kwok YL 2009.}

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