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Inorganic Chemistry Y13 > 5.2.1 Lattice Enthalpy > Flashcards

5.2.1 Lattice Enthalpy Flashcards

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1
Q

why are solid ionic compounds very stable

A

they contain very strong ionic bonds
- electrostatic attractions between oppositely charged ions in the ionic lattice structure
- provides a substantial barrier that must be overcome to break down

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2
Q

how can you measure the strength of ionic bonds in a lattice

A

lattice enthalpy

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3
Q

what is lattice enthalpy

A
  • the enthalpy change
  • that accompanies the formation of one mole of
  • an ionic compound from
  • its gaseous ions
  • under standard conditions
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4
Q

what would be an equation of lattice enthalpy

A

gaseous ions ==> solid ionic compound

  • e.g. K+(g) + Cl-(g) ===> KCl(s)
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5
Q

what is the sign for lattice enthalpy

A

normal symbol with LE in middle

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6
Q

is lattice enthalpy always endo or exo

A
  • always exothermic
  • as you are forming ionic bonds
  • so always negative
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7
Q

how can you indirectly measure lattice enthalpy

A

Born-Haber cycle
- as you cannot measure lattice enthalpy any other way

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8
Q

what are the two routes of a lattice enthalpy cycle

A
  • always start with elements in gaseous state
    1) lattice formation
    2) form gaseous atoms, then ions and then lattice enthalpy
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9
Q

what is the order of lattice enthalpy, longer route

A

1) standard enthalpy change of atomisation
2) first ionisation energy
3) first electron affinity
4) LATTICE ENTHALPY

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10
Q

what is standard enthalpy change of formation

A

enthalpy change that takes place when 1 moles of a compound is formed from its element under standard conditions, with all reactants and products in their standard conditions
- sign = f

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11
Q

what would be the equation of standard enthalpy change of formation

A

elements in their standard state ===> one mole of ionic compound in solid lattice

  • e.g. Na(g) + 1/2 Cl2(g) ===> NaCl(s)
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12
Q

what is the standard enthalpy change of atomisation

A

enthalpy change that takes place for the formation of one mole of gaseous atoms from the elements in their standard states and conditions
- at

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13
Q

what is the equation for atomisation

A

1/2Cl2(g) ===> Cl(g)

  • related to moles, so if we have 1/2 moles, then 1/2 the bond enthalpy
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14
Q

is atomisation endo or exo

A

always ENDO as bonds are being broken to form gaseous atoms
- POSITIVE

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15
Q

what is first ionisation energy

A

the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to one mole of gaseous 1+ ions

-IE

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16
Q

what is the equation of first ionisation energy

A

gaseous atom ===> gaseous 1+ ion

  • e.g. Na(g) ===> Na+(g) + e-
  • can have multiple following dependant on the ion needed
17
Q

is ionisation energy always endo or exo

A

ENDO
- energy is required to overcome the attraction between the negative electron and the positive nucleus
- POSITIVE

18
Q

what is first electron affinity

A

the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

  • EA
19
Q

what is the equation of electron affinity

A

Cl(g) + e- ===> Cl- (g)

20
Q

is electron affinity ENDO or EXO

A

FIRST: exothermic as electron is being added is attracted to the nucleus, so negative
AFTER: endothermic as you are adding a negative electron into a negative ion, which repels, so energy must be put into system for them to react

21
Q

what is always important to remember with a Born-Haber cycle

A

ALWAYS TAKE INTO ACCOUNT THE MOLES

22
Q

enthalpy change of solution

A

enthalpy change that takes place when one mole of solute dissolves into a solvent

  • overall energy energy change associated with the dissolving process
23
Q

what is the equation for enthalpy of solution

A

solid ionic lattice + aq ===> aqueous ions

  • e.g. NaCl(s) + aq ===> Na+(aq) +Cl-(aq)
  • aq represents excess of water molecules
24
Q

is enthalpy change of solution endo or exo

A

could be either

25
Q

how can you determine the value of enthalpy change of solution

A
  • using an experiment
  • using q=mCΔT formula
  • where mass used is the mass of solution, so WATER and IONS
26
Q

what are the two steps of the dissolving process

A

1) the ionic lattice breaks up and forms the separate gaseous ions
2) the separate gaseous ions interact with the polar water molecules and form hydrated aqueous ions

27
Q

what is enthalpy change of hydration

A

the enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

28
Q

what is the equation of enthalpy change of hydration

A

Na+(g) + aq ===> Na+(aq)

29
Q

is enthalpy change of hydration endo or exo

A

can be either, depending of the relative sizes of lattice enthalpy and enthalpy changes of hydration

30
Q

how do you draw a diagram for enthalpy change of solution and hydration

A

1) gaseous ions going down to ionic lattice via lattice enthalpy
2) gaseous ions going down to aqueous ions
3) ionic lattice going up to gaseous ions

31
Q

what are the general characteristics of ionic compounds

A
  • having high melting and boiling point
  • soluble in polar solvents
  • conduct electricity when polar or aqueous
32
Q

how does ionic size affect lattice enthalpy

A
  • ionic radius increases as you go down group
  • so attraction between ions decreases
  • lattice enthalpy becomes less negative
  • so melting point decreases
33
Q

how does ionic charge affect lattice enthalpy

A
  • ionic charge increases
  • attraction between ions increases
  • lattice energy becomes more negative
  • melting point increases
34
Q

how does ionic size effect enthalpy of hydration

A
  • ionic radius increases
  • attraction between H2O molecules and ion decreases
  • hydration energy becomes less negative
35
Q

how does ionic charge affect enthalpy of hydration

A
  • increase in ionic charge
  • attraction with H2O molecules increases
  • more negative hydration energy
36
Q

explain the energy changes that take place when an ionic compound dissolves

A
  • energy equal to the lattice enthalpy is required to be overcome to break the attraction between ions in the lattice
  • water molecules are then attracted, releasing energy equal to hydration energy
37
Q

when does an ionic compound dissolve

A
  • if sum of hyd>lat
  • the overall energy change is exo
  • should dissolve
  • some endo can also dissolve

Inorganic Chemistry Y13 (7 decks)

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