Topic 13A - Lattice Energies Flashcards
Define lattice energy
The energy change when one mole of an ionic solid is formed from its gaseous ions
Define enthalpy change of atomisation
The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state
Define electron affinity
The energy required for one mole of gaseous atom to gain one mole electron to make one mole of a negative ion
What does a more exothermic lattice energy show
Stronger forces of electrostatic attraction between oppositely charged ions
Explain why experimental and theoretical lattice energies are different
Theoretical values assume 100% ionic nature and attractive forces are purely electrostatic.
Experimental values show some covalent nature of an ionic compound
What does it mean when the experimental value is very different to the theoretical value
The electron cloud of the ionic compound is distorted
The ionic compound has covalent nature
There is a greater polarising power
What factors affect polarising power
The charge density of the cation
The radius of the cation
The radius of anion
Define enthalpy change of solution
The enthalpy when one mole of an ionic substance is dissolved in a large excess of water
Define enthalpy change of hydration
When one mole of gaseous ions forms one mole of their aqueous ions under standard conditions
How is enthalpy change of solution calculated
Δhsoln=−Δhlatt + ΣΔhhyd
What does an exothermic enthalpy of solution show
The ionic compound is insoluble
Explain why enthalpy of hydration is always exothermic
Bonds formed between cation and lone pair in water molcules.
