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CHEM 5.2 Energy > 1. Lattice enthalpy > Flashcards

1. Lattice enthalpy Flashcards

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1
Q

Definition Lattice enthalpy

4 points

A

the enthalpy change that accompanies
the formation of one mole of an ionic lattice
from its gaseous ions
under standard conditions

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2
Q

Definition Standard enthalpy change of formation △fHθ

4 points

A

enthalpy change that accompanies
the formation of 1 mole of a compound
from its elements
under standard conditions

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3
Q

Definition of First ionisation energy △ I1 H θ

4 points

A

enthalpy change that accompanies
the removal of 1 mole of electrons
from 1 mole of gaseous atoms
under standard conditions

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4
Q

formation of ionic solid lattice
e.g. potassium chloride
K+(g) + Cl-(g) -> KCl(s) △ LE H θ =-711

3 Key things to notice-

A
  1. ions both gaseous
  2. one mole of substance formed
  3. enthapy change is negative (exothermic) energy is released to surroundings
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5
Q

What does a more exothermic (more negative) lattice enthalpy △ LE H θ indicate?
(2 things)

A
  1. Stronger ionic bonds (Stronger electrostatic interactions).
  2. Higher mpt and bpt (more energy required to overcome electrostatic interactions)
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6
Q

what 2 things cause lattice enthalpy to be more exothermic (negative)?

A
  1. small ions (can get closer together)

2. large charges (large electrostatic forces)

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7
Q
  1. why is it not possible to measure a lattice enthalpy directly?
  2. how do we measure lattice enthalpy?
A
  1. impossible to form 1 mole of an ionic solid from its gaseous ions
  2. Born-Haber cycle
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8
Q

what are the 4 key features of a Born-Haber cycle

A
  1. continuous cycle formed that can start at elements and end at elements
  2. includes one step that shows formation of ionic solid lattice from the gaseous ions (corresponds to lattice enthalpy)
  3. remaining steps show intermediate changes that correspond to key enthalpy changes that can be measured
  4. lattice enthalpy can be calculated by applying Hess’ law. if a reaction can take place via more than 1 route and initial and final conditions are the same the total enthalpy change for each route is the same.
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9
Q

The standard enthalpy change of formation

  1. definition?
  2. exothermic/endothermic?
A
  1. 1 mole of a compound is formed
    from its constituent elements
    in their standard states
  2. usually exothermic for an ionic compound
    bonds are formed
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10
Q

The standard enthalpy change of atomisation

  1. definition?
  2. exothermic/endothermic?
A
  1. 1 mole of gaseous atoms is formed
    from its element
    in its standard state
  2. always endothermic
    bonds have to be broken
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11
Q

The first ionisation energy

  1. definition?
  2. exothermic/endothermic?
A
  1. 1 mole of gaseous 1+ ions are formed
    from gaseous atoms
  2. endothermic
    electron being lost has to overcome attraction to nucleus
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12
Q

The second ionisation energy

  1. definition?
  2. exothermic/endothermic?
A
  1. 1 mole of gaseous 2+ moles formed
    from 1 mole of gaseous 1+ ions.
  2. endothermic
    electron being lost has to overcome attraction to nucleus
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13
Q

The first electron affinity
(electron affinity is the addition of electrons)
1. definition?
2. exothermic/endothermic?

A
  1. 1 mole of gaseous 1- ions is formed
    from gaseous atoms
  2. exothermic
    electron is attracted to the outer shell of an atom by the nucleus
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14
Q

The second electron affinity (addition of electrons)

  1. definition?
  2. exothermic/endothermic?
A
  1. 1 mole of gaseous 2- ions is formed
    from gaseous 1- ions
  2. endothermic
    electron repelled by 1- ion
    repulsion has to be overcome
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15
Q

how can we apply Hess law to Born-Haber cycle

A

enthalpy change of formation= the sum of all the other enthalpy changes
sum of anticlockwise enthalpy changes = sum of clockwise enthalpy changes

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16
Q

what is the symbol for

Lattice Enthalpy

A

△ LE H θ

17
Q

what is the symbol for

Standard Enthalpy hcange of Formation

A

△ f H θ

18
Q

what is the symbol for

The standard enthalpy change of atomisation

A

△ a H θ

19
Q

what is the symbol for

The First Ionisation Energy

A

△ I1 H θ

20
Q

what is the symbol for

The Second Ionisation Energy

A

△ I2 H θ

21
Q

what is the symbol for

The First Electron Affinity

A

△ EA1 H θ

22
Q

what is the symbol for

The Second Electron Affinity

A

△ EA2 H θ

23
Q

The Standard Enthalpy Change of Formation

e.g K(s) + 1/2 Cl2(g) ->

A

K(s) + 1/2 Cl2(g) -> KCl (s)

24
Q

The standard enthalpy change of atomisation

e. g. 1. K(s) ->
2. 1/2 Cl2(s) ->

A
  1. K(s) -> K(g)
    metallic bonds broken
  2. 1/2Cl2(s) -> Cl(g)
    covalent bonds broken
25
Q

The First Ionisation Energy

e.g. K(g) ->

A

K(g) -> K+(g) + e-

26
Q

The Second Ionisation Energy

e.g. Ca+(g)->

A

Ca+(g) -> Ca2+(g) + e-

27
Q

The First Electron Affinity

e.g. Cl(g) ->

A

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

28
Q

The Second Electron Affinity

e.g. O-(g) + e- ->

A

O-(g) + e- -> O2-(g)

CHEM 5.2 Energy (10 decks)

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