3.1.8.1 - born-haber cycles

Question 1

if starting from LiCI (s) how do you create born haber cycles going up
then going down

Answer 1

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)

Question 2

steps going up __ ____ ____ as the steps going down

Answer 2

steps going up is the same as the steps going down

Question 3

when calculating born haber cycles
when you go w the arrow you …
when you go agianst the arrow you…

Answer 3

when you go with the arrow, keep the sign the same
when you go against the arrow change the sign

Question 4

down arrows are ..

Answer 4

exo

Question 5

up arrows are ..

Answer 5

endo

Question 6

if calc enthalpy for 1/2 cl2 and values given is for cl2 what do you do

Answer 6

half the enthalpy

Question 7

is lattice enthalpy exo or endo

Answer 7

exo

Question 8

is enthalpy of formation exo or endo

Answer 8

exo

Question 9

is enthalpy of atomisation endo or exo

Answer 9

endo

Question 10

is ionisation energies endo or exo

Answer 10

endo

Question 11

is first e- affinity endo or exo

Answer 11

exo

Question 12

every other e- affinity apart from 1st

Answer 12

endo

Question 13

we represent atomisation steps …

Answer 13

first w metal
second non metal

Question 14

The greater the value of the lattice enthalpy, the ….

Answer 14

stronger the ionic bonds

Question 15

Smaller ions and higher charge ions give stronger ionic bonding
because

Answer 15

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

Question 16

assumptions of perfect ionic model

Answer 16

✴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).

Question 17

if expirmental value is diff from theortical value it indicates..

Answer 17

compound doesnt follow perfect ionic model - there is some covalent character to the compound

Question 18

when is their covalent character in ionic compounf

Answer 18

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

Question 19

the more polarisation we get…

Answer 19

the more covalent character there will be

Question 20

covalent character to a compound leads to …

Answer 20

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.

Question 21

define enthalpy change of solution

Answer 21

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

Question 22

2 things that need to occur for a substance to dissolve

Answer 22

substance bonds must break (endo)
new bonds formed between solvent and substance (exo)

Question 23

explain how a substance is dissolved

Answer 23

ionic lattice in solid form
substance bonds broken to create to create free moving

Question 24

steps of dissolving a solid ionic lattice

Answer 24

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

Question 25

most ionic compounds dissolve in _____ solvents

Answer 25

most ionic compounds dissolve in polar solvents

Question 26

how do ionic compounds dissolve in polar solvents

Answer 26

the delta positive H is attracted to negative ions and the delta neg oxygen is attracted to positive ions, the struc starts to break down

Question 27

the water molecules surrond the ions in a process called …

Answer 27

hydration

Question 28

what must happen for hydration to occur

Answer 28

new bonds formed must be the same strength or greater than those broken
if not then the sub is very unlikely to dissolve. soluble sub tend to have exothermic enthalpies of solution bc of this

Question 29

enthalpy of hydration

Answer 29

1 mole of aqueous ions are formed from gaseous ions
Na+ (g) + aq –> Na+(aq)
Cl-(g) + aq –> Cl-(aq)

Question 30

extra steps needed for born haber cycle of group elements

Answer 30

Second ionisation energy of Mg needs to be included because Mg forms 2+
ions.
* Atomisation of Cl is multiplied by 2 as there are 2 moles of Cl for
every 1 mole of Mg
* First electron affinity of Cl is multiplied by 2 as there are 2 moles
of Cl- formed in the ionic lattice.

Question 31

the bigger the difference in lattice enthalpy

Answer 31

the more polarisation you have
the bigger the lattice enthalpy