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?
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