chemistry - unit 4 - section 1: thermodynamics

born haber cycles

1. enthalpy of formation

2. enthalpy of atomisation of chlorine

3. enthalpy of atomisation of lithium

4. 1st ionisation of lithium

5. 1st electron affinity of chlorine

6. lattice enthalpy of formation of lithium chloride

calculate lattice enthalpy

calculating other parts of the cycle

extended born-haber cycle with double ions

theoretical and experimental lattice enthalpies

theoretical and experimental values of lattice enthalpies can be different depending on how ‘purely ionic’ the compound is

theoretical lattice enthalpies can be calculated from data assuming a perfectly ionic model

a perfectly ionic model is…

1. ions that are perfectly spherical

2. the charge is evenly distributed in this sphere (point charges)

actual and theoretical values of lattice enthalpies

• if the calculated value is different from theoretical value it tells us that the compound being experimented on doesn’t follow the perfectly ionic model and has some covalent characteristics

• the more polarisation we get, the more covalent character there will be

• most of the time the positive ion distorts the charge distribution in the negative ion. we say the positive ion polarises the negative ion