Born Haber Cycle Tricks and Tips

Step 1Draw a Datum line. In the Datum line write the equation for formation. In the formation equation include state symbols and one mol of compound is formed.It is an Exothermic reaction because it involves bond forming so the arrow point downwards.Step 2Atomisation is an endothermic process because bonds have to be broken. 1 mol of gaseous atom is formed for example in that process Li(s)----->Li(g) and ½Cl2(g) ——> Cl(g), Cl2(g) ——> to 2Cl(g). If it is 2 then times the value by 2. This process happens for each element.Step 3First ionisation energy is an endothermic process because the electron being lost has to overcome the attraction from the nucleus, in order to  leave the atom. It only occurs for metals only. E.g Na(g) ——> Na+1(g) +e- Only this part is written. If it was 2Na(g) ——> 2Na+(g)+ 2e-. If this is the case times the value by 2.Second ionisation energy is an endothermic process and group 2 have second ionisation energy..   Mg+ (g) -——> Mg2+ (g) + 2e¯Step 4 First electron affinity is an exothermic process so the arrow is pointing downwards. This is only for the non metals. It is exothermic because the electron  is gained and attracted into the outer shell of an atom by the nucleus. Equations are like Cl(g) +e- -----> Cl-(g)Group 6 elements have two electron affinity. Second electron affinity is endothermic because negative ion repels the negative charged electron. For. e.g O-(g) + e- ------> O2-(g)Step 5  Lattice enthalpy is negative and formed from gaseous ions under standard conditions. 

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