A2 enthalpy.

Question 1

What is lattice enthalpy?

Answer 1

The measure of the strength of the ionic bonds in a giant ionic lattice
The enthalpy change that accompanies the formation of one mole of an ionic compounds from it’s gaseous ions under standard conditions.

Question 2

Value for lattice enthalpy.

Answer 2

Always negative
As is an exothermic change.

Question 3

Born-haber cycles.

Answer 3

Used when enthalpy change can’t be measured directly
Practice questions!!!

Question 4

Formation of gaseous atoms.

Answer 4

Elements in standard state–> gaseous atoms
Endothermic
Breaks bonds.

Question 5

Formation of gaseous ions.

Answer 5

Gaseous atoms–> positive and negative gaseous ions
Endothermic.

Question 6

Lattice formation.

Answer 6

Gaseous ions–>solid ionic lattice
Lattice enthalpy
Exothermic.

Question 7

Route 2 from standard diagram.

Answer 7

Elements in SS–>ionic lattice
Enthalpy change of formation
Exothermic.

Question 8

Standard enthalpy change of formation.

Answer 8

1 mole of a compound is formed from it’s elements under SC
All reactants and products in SS
Compound=an ionic compound in it’s solid lattice.

Question 9

Standard enthalpy change of atomisation.

Answer 9

Formation of 1 mole of gaseous atoms from it’s elements in SS under SC
Endothermic
Bonds broken
When a gas in SS, atomisation enthalpy change is related to the bond enthalpy of the bond being broken.

Question 10

First ionisation energy.

Answer 10

Enthalpy change needed to remove 1 electron
from each atom in a mole of gaseous atoms to form 1 mole of gaseous 1+ ions
Endothermic.

Question 11

Electron affinity.

Answer 11

Measure energy required to gain electrons
Enthalpy change that takes place when 1 electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions
Exothermic.

Question 12

Successive electron affinities.

Answer 12

Needed when anion has a charge greater than 1-
2nd are always endothermic
Energy is needed to be put in to force the negatively charged electron onto the negative ion
Therefore would require 2 energy changes.

Question 13

Standard enthalpy change of solution.

Answer 13

Change that takes place when 1 mole of solute dissolves in a solvent
Exothermic or endothermic
Delta- oxygen attracted to the positive
Delta+ hydrogen attracted to the negative.

Question 14

Description of the dissolving process.

Answer 14

1) Ionic lattice breaks up:
Forms separate gaseous ions
Opposite energy change from lattice formation
endothermic
2) Separate gaseous ions interact w/ polar H2O molecules to form hydrated aqueous ions
Enthalpy change of hydration
Exothermic.
DIAGRAMS/practice questions.