Born Haber cycles

Question 1

The Standard Enthalpy of Formation, ∆Hɵf

Answer 1

The enthalpy change when one mole of a compound is formed
from its elements
under standard conditions, all reactants and products in their standard states.
e.g. Na(s) + ½Cl2(g)  NaCl(s)

Question 2

First Ionisation Enthalpy, 1st∆Hɵi

Answer 2

The standard enthalpy change when one mole of electrons
is removed from one mole of gaseous atoms
to give one mole of gaseous ions each with a single positive charge.
e.g. Ca(g) —–> Ca+(g) + e

Question 3

The Standard Enthalpy of Atomisation, ∆Hɵat

Answer 3

The enthalpy change when one mole of gaseous atoms are formed
from an element in its standard state.
e.g. ½ Br2(l) ——> Br(g)

Question 4

Mean Bond Enthalpy ΔHBEΘ

Answer 4

The enthalpy change when one mole of gaseous molecules
each break a covalent bond to form two free radicals
averaged over a range of compounds.
e.g. Br2(l) —–> 2Br(g)

Question 5

First Electron Affinity, 1st∆Hɵea

Answer 5

The standard enthalpy change when one mole of gaseous atoms
is converted into a mole of gaseous ions
each with a single negative charge under standard conditions.
e.g. O(g) + e- —–> O-(g)

Question 6

Lattice Formation Enthalpy ΔHLFΘ

Answer 6

The standard enthalpy change when one mole of solid ionic compound
is formed from its gaseous ions.
e.g. Mg2+(g) + 2Br-(g) ——> MgBr2(s)

Question 7

Lattice Dissociation Enthalpy ΔHLDΘ

Answer 7

The standard enthalpy change when one mole of solid ionic compound
dissociates into its gaseous ions.
e.g. MgBr2(s) ——> Mg2+(g) + 2Br-(g)

Question 8

Standard Enthalpy of Hydration ΔHhydΘ

Answer 8

The standard enthalpy change when one mole of gaseous ions
is converted into one mole of aqueous ions.
e.g. Cl-(g) + aq ——> Cl-(aq)

Question 9

Standard Enthalpy of Solution ΔHsolΘ

Answer 9

The standard enthalpy change when one mole of solute dissolves
to form its aqueous ions
e.g. NaCl(s) + aq —–> Na+(aq) + Cl-(aq)

Question 10

Definition of an ionic bond:

Answer 10

The strong electrostatic attraction between oppositely charged ions.

Question 11

The strength of an ionic bond will increase dependent on:

Answer 11

• The size of the ions - Smaller ions have a stronger attraction
• The charge of the ions – Higher charged ions have a stronger attraction

Question 12

Stronger ionic lattices have a more……. lattice ………enthalpy

Answer 12

exothermic
formation

Question 13

Stronger ionic lattices have a more ………… lattice …………enthalpy

Answer 13

endothermic
dissociation

Question 14

Model name-theoretical-experimental

Model name- perfect ionic model-born Haber cycle

Assumption made about ions-perfect spheres/point charges-polarisable ions

Nature of bonding-purely ionic-ionic plus some covalent character

Answer 14

Write from memory

Question 15

State the meaning of the term enthalpy change

Answer 15

Heat energy change at constant pressure

Question 16

Give one reason why the bond enthalpy you have calculated is different from the mean bond enthalpy quoted in a data book

Answer 16

Data book value derived from a number of different compounds

Question 17

The enthalpy of combustion determined experimentally is less exothermic than that calculated using enthalpies of formation

Give one possible reason for this, other than heat loss

Answer 17

-Incomplete combustion
-Fuel evaporating
- Reaction not under standard condition

Question 18

Explain why the value given for O=O bond enthalpy in part b is not a mean value

b) the bond enthalpy for O=O is +496 kJmol-1

Answer 18

O2 is the only substance that had O=O

So can’t calculate a mean