3.1.8.1 - born-haber cycles
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if starting from LiCI (s) how do you create born haber cycles going up then going down
enthalpy of formation (exo) -> Li(S) + 1/2CL2(g) enthalpy of atomisation of chlorine Li(s) + cl(g) enthalpy atomisation of lithium Li(g) + cl (g) 1st ionisation energy of lithium li+(g) + cl(g) + e- going down.. 1st electron affinity of chlorine (exo) Li+(g) + Cl-(g) lattice enthalpy of formation of lithium chloride LiCI (s)
steps going up __ ____ ____ as the steps going down
steps going up is the same as the steps going down
when calculating born haber cycles when you go w the arrow you … when you go agianst the arrow you…
when you go with the arrow, keep the sign the same when you go against the arrow change the sign
down arrows are ..
exo
up arrows are ..
endo
if calc enthalpy for 1/2 cl2 and values given is for cl2 what do you do
half the enthalpy
is lattice enthalpy exo or endo
exo
is enthalpy of formation exo or endo
exo
is enthalpy of atomisation endo or exo
endo
is ionisation energies endo or exo
endo
is first e- affinity endo or exo
exo
every other e- affinity apart from 1st
endo
we represent atomisation steps …
first w metal second non metal
The greater the value of the lattice enthalpy, the ….
stronger the ionic bonds
Smaller ions and higher charge ions give stronger ionic bonding because
Smaller ions are more closely packed in the lattice, so are more attracted to each other, resulting in high lattice enthalpy. * Ions with high charge have stronger electrostatic forces of attraction between the ions which results in high lattice enthalpy
assumptions of perfect ionic model
✴The bonding in the compound is completely ionic. ✴The ions are regarded as perfect spheres + are not distorted (i.e. have their charge evenly distributed around them).
if expirmental value is diff from theortical value it indicates..
compound doesnt follow perfect ionic model - there is some covalent character to the compound
when is their covalent character in ionic compounf
a small and highly charged cation can distort a large anion so that there is covalent character to the ‘ionic compound’. This means that ions are distorted and not spherical (That IS assumed by the perfect ionic model) positive ion polarises negative ion
the more polarisation we get…
the more covalent character there will be
covalent character to a compound leads to …
This leads to a difference between the values of the experimental lattice enthalpy and the theoretical lattice enthalpy. The greater the difference in the values, the greater the covalent character in the compound.
define enthalpy change of solution
the enthalpy change when one mol of an ionic sub is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution
2 things that need to occur for a substance to dissolve
substance bonds must break (endo) new bonds formed between solvent and substance (exo)
explain how a substance is dissolved
ionic lattice in solid form substance bonds broken to create to create free moving
steps of dissolving a solid ionic lattice
1) ionic lattice in solid form + water 2) substance binds broken to create free moving ions 3) bonds formed between ions and water - ions are hydrated