1.1 Lattice Enthalpy Flashcards

1
Q

Define ionic bonds

A

Strong electrostatic forces of attraction between oppositely charged ions

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2
Q

Define lattice enthalpy

A

the enthalpy change when one mole of an ionic compound is converted to gaseous ions

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3
Q

Give an equation to express the lattice enthalpy of sodium chloride

A

NaCl(s) → Na+ (g) + Cl- (g)

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4
Q

Describe the value of lattice enthalpy

A
  • will be endothermic (+ve) as energy is required to break the ionic bonds
  • a large value for lattice enthalpy shows there are strong electrostatic forces of attraction between the oppositely charged ions in the lattice.
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5
Q

Define the standard enthalpy change of formation

A

The energy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

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6
Q

Give an equation to express the standard enthalpy change of formation of potassium chloride

A

K(s) + ½ Cl2(g) → KCl(s)

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7
Q

Define standard enthalpy change of atomisation

A

The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state

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8
Q

Give an equation to express the standard enthalpy change of atomisation of potassium

A

K(s) → K(g)

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9
Q

Give an equation to express the standard enthalpy change of atomisation of chlorine

A

½ Cl2(g) → Cl(g)

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10
Q

Define the standard bond dissociation enthalpy

A

The enthalpy change required to break 1 mol of a covalent bond, everything being in the gas state.

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11
Q

Give an equation to express the standard bond dissociation enthalpy of chlorine

A

Cl2(g) → 2Cl(g)

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12
Q

Define first ionisation energy

A

The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

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13
Q

Give an equation to express the first ionisation energy of potassium

A

K(g) → K+(g) + e-

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14
Q

define second ionisation energy

A

The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

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15
Q

give an equation to express the second ionisation energy of calcium

A

Ca+(g) → Ca2+(g) + e-

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16
Q

Define first electron affinity

A

the enthalpy change when one mole of gaseous atoms is converted into gaseous ions with a single negative charge.

17
Q

give an equation to express the first electron affinity of chlorine

A

Cl(g) + e- → Cl-(g)

18
Q

Define second electron affinity

A

The enthalpy change when one mole of gaseous 1- ions is converted into one mole of gaseous ions with a double negative charge.

19
Q

Give an equation to express the second electron affinity pf oxygen

A

O-(g) + e- → O2-(g)

20
Q

In gaseous elements such as oxygen and chlorine, which two enthalpy values can be equated?

A

enthalpy of atomisation and bond dissociation enthalpy

21
Q

What enthalpy changes are exothermic?

A

enthalpy of formation

first electron affinity

22
Q

what enthalpy changes are endothermic?

A
lattice enthalpy
enthalpy of atomisation
bond dissociation enthalpy
first ionisation energy
second ionisation energy
23
Q

what does a +ve ∆H imply?

A

endothermic enthalpy change

24
Q

what goes a -ve ∆H imply?

A

exothermic enthalpy change

25
Q

Describe the enthalpy changes found clockwise in an enthalpy diagram

A
TOP -> BOTTOM
- Electron affinities
- Lattice enthalpy
BOTTOM -> TOP
- Enthalpy of formation
- Enthalpy of atomisation
- Ionisation energies
- Bond dissociation enthalpy (or atomisation)
26
Q

what does a large endothermic enthalpy value mean?

A

there is a large electrostatic force of attraction between the oppositely charged ions, therefore the bonds are very strong

27
Q

What factors govern the size of lattice enthalpy?

A

ionic size

ionic charge

28
Q

how does ionic size govern the size of lattice enthalpy?

A

Lattice enthalpy becomes less endothermic (less positive) as the size of the negative ion increases.
This indicates weaker attraction between ions and hence weaker ionic bonding

29
Q

how does ionic charge govern the size of lattice enthalpy?

A

Charge increases and produces a greater attraction between these positive ions and negative ions. The ionic radius decreases, resulting in the ions in the lattice being closer together, producing more attraction.
Therefore as charge increases, lattice enthalpies become more endothermic, therefore more positive.

30
Q

what types of compounds would you expect to have the most positive lattice enthalpies?

A

those with small, highly charged ions

31
Q

define enthalpy of solution

A

The enthalpy change when one mole of a solute dissolves in water.

32
Q

define enthalpy of hydration

A

The enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions.

33
Q

What processes occur when an ionic solid dissolves and why?

A
  1. breakdown of the ionic lattice - overcoming the attractive forces requires energy
  2. Hydration of the gaseous ions - gaseous ions bond with the water molecules
34
Q

What equation connects enthalpy of solution and enthalpy of hydration?

A

Enthalpy of solution = lattice enthalpy + enthalpy of hydration