5.2.1 - Lattice enthalpy
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Lattice enthalpy
Enthalpy change when one mole of an ionic compound is formed from the gaseous ions under standard conditions
Is lattice enthalpy exo/endothermic
Exothermic
What does lattice enthalpy measure
Ionic bond strength
Why is breaking ionic lattice endo
Energy is required to overcome ionic bonds Stronger bonds –> more +ve
General formula for BHC w/ formation
Formation Atomisation ^ Atomisation ^ 1st IE ^ 1st EA LE
Enthalpy of atomisation
Standard enthalpy change when one mole of gaseous atoms is formed from its elements in their standard states Always +ve
Enthalpy of 1st electron affinity
Enthalpy change of adding one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions Exothermic
Enthalpy of 2nd electron affinity
Enthalpy change of adding one electron to each ion in one mole of gaseous ions to form one mole of gaseous 2- ions Endothermic
Factors affecting LE
Ionic size Ionic charge
How does ionic size affect LE
Smaller ions can pack together more closely in a lattice and attract each other more strongly Leads to a more exothermic LE
How does ionic charge affect LE
Ions w/ higher charges attract each other more strongly As the charge on the cations increase, LE becomes more exo
When is enthalpy of hydration/solution used
Ions that contain more than one element eg. NO3-, CO3^2-, SO4^2- and salts
Enthalpy of solution
Enthalpy change that takes place when 1 mole of an ionic compound dissolves completely in water Can be endo/exothermic
Enthalpy of hydration
Enthalpy change that takes place when 1 mole of gaseous ions dissolves in water to form 1 mole of aq ions Always exo
Factors affecting Enthalpy of hydration
Ionic size Ionic charge
How does ionic size affect enthalpy of hydration
Smaller ions have more exothermic enthalpies of hydration Grreater charge density means stronger bonding w/ water
How does ionic charge afffect enthalpy of hydration
Higher charge ions have more exothermic enthalpies of hydration due to stronger bonds w/ H2O due to dipoles
General formula for BHC w/ hydration
LE Hydration Hydration Solution ^
How does LE change across a period
Ionic charge increases Ionic radius decreases Stronger ionic bonds due to increased attraction between ions so w/ more -ve LE Sronger bonds w/ H2O –> more - ve hydration enthalpies
How does LE change down a group
Atomic charge stays the same Ionic radius increases Charge density decreases so weaker ionic bonds due to weaker forces of attraction –> less -ve LE Weaker bonds w/ H2O due to weaker dipoles –> less -ve hydration enthalpies
Why is the 2nd IE more endo than the 1st
X^+ is smaller than X Greater nuclear attraction
Why is the second EA +ve
More energy is required to overcome the repulsion between X^- and the electron
Why is the first EA -ve
Involves electron experiencing attraction to the nucleus