Up Learn – A Level Chemistry (aqa) – Constructing Born-Haber Cycles

Summary of Lattice Enthalpy

Bond dissociation enthalpy is defined as the enthalpy change when one mole of a covalent bond is broken to give separated atoms, with everything in the gas state.

More videos on Constructing Born-Haber Cycles:

Summary of Lattice Enthalpy

Lattice Enthalpy: Atomisation and Bond Dissociation

Lattice Enthalpy: Electron Affinity

Summary of Born Haber Cycles

Exothermic and Endothermic Electron Affinity

Alternative Born-Haber Cycles (article)

Labelling Enthalpy Changes (article)

Perfect Ionic Model: Covalent Character

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Up Learn – A Level Chemistry (AQA)

Constructing Born-Haber Cycles

1. Introduction to Lattice Enthalpies
2. Enthalpies Recap
3. Lattice Enthalpy
4. Predicting Lattice Enthalpies
5. Finding Lattice Enthalpy Experimentally
6. Finding Lattice Enthalpy Using a Hess Cycle
7. Separation
8. Atomisation
9. Atomisation and Bond Dissociation
10. Removing Electrons
11. Adding Electrons
12. Electron Affinity
13. Representing Different Enthalpy Changes
14. Summary of the Alternate Route
1. The Aftermath of WWI
2. Exo or Endo?
3. Exothermic and Endothermic Electron Affinity
4. Constructing Born Haber Cycles: First Steps
5. Constructing Born Haber Cycles: Adding Atomisation
6. Constructing Born Haber Cycles: Removing Electrons
7. Constructing Born Haber Cycles: Adding Electrons
8. Alternative Born-Haber Cycles
9. Labelling Enthalpy Changes
10. Labelling Born-Haber Cycles
11. Constructing Born-Haber Cycles
12. Finding Lattice Enthalpy using Born-Haber Cycles
13. Calculating Lattice Enthalpies using Born-Haber Cycles
14. Constructing Born Haber Cycles: Adding More Than One Electron
15. Calculating Lattice Enthalpy Using More Complex Born-Haber Cycles
16. Calculating Enthalpies Other Than Lattice Enthalpy Using Born-Haber Cycles
1. Theoretical vs Experimental Lattice Enthalpies – Introduction
2. Calculating Lattice Enthalpies Quickly
3. Theoretical vs Experimental
4. Perfect Ionic Model: Covalent Character
5. Polarisation
6. Polarising Power
7. Polarisability
8. Comparing Covalent Character
9. The Curious Case of the Silver Halides
1. An Alternative Route For Lattice Enthalpy
2. Dissolving Salts In Water
3. The Enthalpy of Solution
4. Enthalpy Changes and The Enthalpy of Solution
5. Can I Feel The Enthalpy of Solution?
6. Gaseous Ion Hydration
7. Enthalpy of Hydration
8. Factors Affecting the Enthalpy of Hydration
9. Constructing an Alternative Route for Lattice Enthalpy
10. Calculating Lattice Enthalpy
11. Energy Level Diagrams, Hydration and Solution
12. Energy Level Diagrams and Exothermic Enthalpies of Solution
13. Converting SHL Cycles into Energy Level Diagrams

Last time we looked at enthalpy of atomisation

…Which is defined as the enthalpy change when one mole of gaseous atoms is formed from an element in its standard state.

And we’ve also looked at enthalpy of bond dissociation

…Which we’ve seen before is defined as the enthalpy change when one mole of a bond is broken to give separated atoms, which everything in the gas state.

And, sometimes these two enthalpy changes can be related

For example, the enthalpy of atomisation of chlorine is equal to half the bond dissociation enthalpy of a Cl-Cl bond

And that’s because, “to atomise chlorine gas such that we have 1 mol of chlorine atoms, we break.. ½ a mole of Cl-Cl bonds, form separated atoms, and everything is in the gas state

Similarly, the enthalpy of atomisation of oxygen is equal to half the bond dissociation enthalpy of an oxygen-oxygen double bond bond

And that’s because when we atomise oxygen, we break ½ a mole of oxygen-oxygen double  bonds, form separated atoms, and everything is in the gas state

And lastly, by the same logic, the enthalpy of atomisation of fluorine is equal to…

The enthalpy of atomisation of fluorine is equal to half the bond dissociation enthalpy of a F-F  bond

And that’s because when we atomise fluorine, we break ½ a mole of F-F bonds, forming separated atoms, and everything is in the gas state

So for all three of these elements we can relate their enthalpy of atomisation to their bond dissociation enthalpy 

But be warned, this doesn’t work for every element.

For example, it doesn’t work for bromine.. 

And that’s because, even though we’re still breaking half a mole of br-br bonds

And even though we’re still forming separated atoms

Bromine isn’t a gas in its standard state, it’s a liquid, so this relationship doesn’t hold up

Nor does it work for sodium

Because sodium’s a metal in its standard state, and we can only calculate bond dissociation enthalpies for covalent bonds.  

In fact, we can only relate bond dissociation enthalpy to enthalpy of atomisation if the element is gaseous and covalently bonded in its standard state. 

So, for which of these elements can we relate enthalpy of atomisation and bond dissociation enthalpy?

These elements are gaseous and covalently bonded in their standards states, so we can relate their enthalpy of atomisation to their bond dissociation enthalpies

But these elements aren’t, so we can’t.

So, we’ve now fully covered the second step of our alternative route: atomisation

And next, we’ll look at the third step: removing electrons 

But first, to sum up… 

We can sometimes relate an element’s enthalpy of atomisation to its bond dissociation enthalpy, but only when

But only when it’s gaseous and covalently bonded in its standard state.