5.2.1 Lattice Enthalpy Flashcards
Define lattice enthalpy
The enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions.
Give an equation demonstrating lattice enthalpy. Use NaCl.
Na⁺(g) + Cl⁻(g) → NaCl(s)
Is lattice enthalpy exothermic or endothermic?
Exothermic
What is lattice enthalpy used for?
As a measure of the strength of ionic bonding in a giant ionic lattice. The solubility of the ionic compound can then be predicted.
Define the enthalpy change of atomisation
The enthalpy change when 1 mole of gaseous atoms are formed from an element in its standard state.
Give an equation demonstrating the enthalpy change of atomisation. Use Na, Cl₂ and I₂.
Na(s) → Na(g)
- 5Cl₂ → Cl(g)
- 5I₂ → I(g)
Define first electron affinity
The enthalpy change when every atom in 1 mole of gaseous atoms acquires an electron to form 1 mole of gaseous 1⁻ ions.
Give an equation demonstrating the first electron affinity of chlorine.
Cl(g) + e⁻ → Cl⁻(g)
Is the enthalpy change of atomisation exothermic or endothermic?
Endothermic
Is first electron affinity exothermic or endothermic?
Exothermic
Define second electron affinity
The enthalpy change when every ion in 1 mole of gaseous 1⁻ ions acquires an electron to form 1 mole of gaseous 2⁻ ions.
Give an equation demonstrating the second electron affinity of chlorine ions.
Cl⁻(g) + e⁻ → Cl²⁻(g)
Is second electron affinity exothermic or endothermic? Why?
Endothermic. The negative electron experiences repulsion by the already negative ion. It requires more energy to overcome the repulsion than is released.
Define the enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states.
Is enthalpy change of formation exothermic or endothermic?
Both
