1
Q
Enthalpy changes during formation of ionic compounds
A
- Formation of free (g) atoms frm elements, std state
- Form ions (add/remove e-)
- Form ionic compound (attraction of ions)
2
Q
Enthalpy change of atomization
A
- energy absorbed
- one mole of (g) atoms formed frm element
- std conditions
- Metals: Strong metallic bond broken
- Non-metals: Strong covalent bonds broken
- always +ve (endothermic) as energy needed to break bonds
3
Q
Ionization energy
A
- IE is always +ve (endo)
- energy required to overcome attractive force between +ve charged nucleus and electron being removed
- lower IE value, easier to form cation
- 2nd IE > 1st IE
- electrostatic attraction forces between remaining electrons and +ve nucleus stronger than 1st IE
4
Q
1st IE
A
- energy needed to remove 1 mol of e-
- from 1 mol of (g) atoms
- form 1 mol of (g) cations
- under std conditions
- e.g. Mg (g) –> Mg+ (g) + e-
5
Q
2nd IE
A
- energy needed to remove 1 mol of e-
- from 1 mol of free (g) unipositive ions of that element
- e.g. Mg+ (g) –> Mg2+(g) + e-
6
Q
1st Electron affinity (EA) (Non-metal)
A
- enthalpy change when 1 mol of (g) atoms gain 1 mole of e-
- form 1 mol of (g) anions
- e.g. O(g) + e- –> O- (g)
7
Q
2nd electron affinity (EA)
A
- energy change when 1 e- added
- to each mol of free (g) uninegative ions of that element
- O- (g) + e- –> O2-
8
Q
Electron affinity
A
- 1st EA exothermic, 2nd EA endothermic
- 2nd EA: electronic repulsion when 2nd electron added to a negative ion
- more electronegative the element, more exo the 1st EA
9
Q
Lattice enthalpy
A
- LE of ionic compound is the enthalpy change
- when 1 mol of ionic solid
- separated into its (g) ions
- under std conditions
- cannot be determined directly from experiments
- formation of ionic crystals frm (g) ions cannot be done in lab
- LE calculated from other experimentally determined enthalpy changes using Born-Haber cycle
10
Q
Born-Haber cycle
A
- enthalpy cycle
- calculate the std enthalpy change of a particular step or stage
- in formation of ionic compound
