Born håber cycles

  • Created by: Hindleyc
  • Created on: 25-11-18 18:29
Why do we have born haber cycles?
Lattice enthalpy cannot be determined directly so we calculate it indirectly by making use of changes for which data is available and link them together in an enthalpy cycle- born haber cycle
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Tips
Pay attention to state symbols and direction of arrows, usually all data pieces given except one that needs to be calculate
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What could the data for the atomisation of chlorine be given as?
Bond energy for cl-cl bond (=2x atomisation)
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If drawing what order
Atomise, Ionise, Atomise, Electron affinity, then lattice form or dissociation and formation
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What if formation?
arrow down
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What if dissociation
arrow up
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Where do you go from
start of arrow
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Check for
How many ionisation energies
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Why is the second electron affinity for oxygen endo
Takes energy to overcome repulsive forces between negative ion and electron
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What is the most thermodynamically stable?
When the enthalpy of formation is more exothermic- one that forms
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Why does lattice enthalpy inc from CaCl to CaCl3
+ve charge on calcium ion becomes bigger
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What is enthalpy of lattice formation largely a balance between?
ionisation energy and the lattice enthalpy
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What is the strength of a lattice formation depend on
Size of ion, charges on the ion
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how does size of ion affect it
- larger the ions the less -ve the enthalpies of lattice formation (i.e weaker lattice) as ions are larger the charges become further apart so have a weaker attractive force between them
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how does charge of ion affect it
bigger the charge of the ion, the greater the attraction between the ion so the stronger the lattice enthalpy (more -ve values)
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What does LE become as you go down the group?
less -ve
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What do theoretical lattice enthalpies assume
perfect ionic model where ions 100% ionic& spherical and attractions purely electrostatic (charge evenly distributed)
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When is there a tendency towards covalent character in ionic substances?
When- +ve ion is small, +ve ion has multiple charges, -ve ion is large, -ve ion has multiple -ve charges
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What happens when a compound has some covalent character
Tends towards giant covalent so lattice stronger than if 100% ionic therefore born haber value would be larger than theoretical value
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What causes differences between theoretical and born haber experimental lattice enthalpies
B H l.e is real experimental value, when a compound shows covalent character theoretical and born haber lattice enthalpies differ. the more covalent character the bigger the differences b/w values
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What happens when a -ve ion becomes distorted and more covalent?
becomes polarised . metal cation that causes polarisation is called more polarising if it polarises the negative ion
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What happens when 100% ionic
Ions spherical, theoretical and BH value is same
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Ionic with covalent character?
Charge cloud distorted. theoretical and BH values differ
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Other cards in this set

Card 2

Front

Tips

Back

Pay attention to state symbols and direction of arrows, usually all data pieces given except one that needs to be calculate

Card 3

Front

What could the data for the atomisation of chlorine be given as?

Back

Preview of the front of card 3

Card 4

Front

If drawing what order

Back

Preview of the front of card 4

Card 5

Front

What if formation?

Back

Preview of the front of card 5
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