Ionic compounds Flashcards
1
Q
What must be done to form a lattice?
A
- atomisation of metal
- atomisation of non metal
- ionisation of metal
- electron affinitiy of non metal
- formation of lattice
2
Q
How can a step of this process be calculated?
A
- Hess’s law tells us that the total enthalpy change for a chemical reaction is the same whatever route is taken
- provided conditions are constant
- any quanitites can be claculated
- using a Born-HAber cycle
3
Q
A
4
Q
What is a Born-Haber cycle?
A
- a thermochemical cycle that includes all the enthalpy changews involved in the formation of an ioninc compound
5
Q
What do Born-Haber cycles begin with?
A
all elements in their standard states
0 enthalpy
6
Q
What are the steps of a Born-Haber cycle?
starting from the bottom left going clockwise
A
- atomisation of metal (2nd row bottom left)
- atomisation of non metal
- ionisation of metal
- electron affinity of non metal
- enthalpy of lattice formation
7
Q
Which ways do the arrows point?
A
- positive enthalpy change goes up
8
Q
What is the clockwise rule for Born-Haber cycle?
A
clockwise arrows = anticlockwise arrows
rearange to find desired value
9
Q
what is the perfect ionic model?
A
ions regarded as point charges
10
Q
why is the enthalpy of lattice dissociation for AgCl greater than observed value?
A
has some covalent characteristics
forces in lattice stronger than pure ionic attraction
