The Born Haber Cycle For Aluminium Oxide

The born haber cycle for aluminium oxide is a useful way of visualising the energy changes involved in forming an ionic compound from an alkali metal and a non-metal such as oxygen or halogen. It is important to understand the energy changes in chemical reactions as it helps us predict what will happen during a reaction and whether it will be feasible for a given thermodynamic system.

The chemistry behind this is quite complex and it can be difficult to get the hang of but once you know what the cycle does you can use it for other reactions. The key is to watch the sign of each step. For example, adding up all the values in a cycle for an ionic compound requires you to add ions together, which will result in a negative sign. This is where many people go wrong. Getting the hang of it takes practice, but once you have it you can use it for other reactions and you can start to predict what will happen.

It is also important to note that lattice enthalpies and lattice energies are different things. Physics-style calculations of lattice enthalpy assume that a compound is completely ionic and therefore the bonds are purely electrostatic, but this is not always true. Large differences between theoretical and experimental values of lattice enthalpy suggest that the bonding is showing some covalent character, for example through distortion of electron density which results in polarisation. This is why a solid magnesium oxide has a higher lattice enthalpy than sodium chloride, even though their crystal structures are identical.