5.2.1 Lattice Enthalpy

enthalpy change

heat energy transferres in a reaction at constant pressure

enthalpy change symbol

ΔH

units of enthalpy change

kJ mol^-1

enthalpy change of atomisation of an element 

enthalpy change when 1 mole of gaseous atms is formed from an element under standard conditions

enthalpy change of atomisation symbol

enthalpy change of atomisation of cl

enthalpy change of atomisation of a compound

enthalpy change when 1 mole of a compound is converted to gaseous atoms under standard conditions

enthalpy change of atomisation of NaCl

second ionisation energy

energy needed to change 1 mole of gaseous 1+ ions atoms into 1 mole of gaseous 2+ ions

first electron affinity

energy needed to change 1 mole of gaseous atoms into 1 mole of gaseous 1- ions

second electron affinity

energy needed to change 1 mole of gaseous 1- into 1 mole of gaseous 2- ions

lattice enthalpy

enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

lattice enthalpy symbol

lattice enthalpy of NaCl

enthalpy change of hydration

enthalpy change when 1 mole of gaseous ions is dissolved in water under standard conditions

enthalpy change of hydration symbol

enthalpy change of hydration of Na

enthalpy change of solution

enthalpy change when 1 mole of solute is dissolved in a solvent such as water under standard conditions

enthalpy change of solution symbol

enthalpy change of solution of NaCl

what is lattice enthalpy a measure of

ionic bond strength

Factors affecting lattice enthalpy

• ionic charge

  • ionic radius

how does ionic charge affect lattice enthalpy

• the higher the charge on the ions

• the stronger the electrostatic attraction between the ions

• so the more energy is released when an ionic lattice forms.

• more energy released meand lattice enthalpy will be more negative

• so lattice enthalpy for compounds with 2+ or 2- iions are more negative than 1+ or 1- ions

how does ionic radius affect lattice enthalpy

the smaller the ionic radii of the ions involved the higher the charge density of the ion this means the electrostatic attraction between the ions is greater so the lattice enthalpy is mor exothermic

born haber cycle example

what happens if there is 2 of a molecle in bohn haber cycle 

times enthalpy change of atomisation for element by 2 and either is ionisation energy or electron affinity by 2

what happens when a solid ionic lattice dissolves in water

• bonds between ions break to give gaseous ions which is endothermic,enthalpy change is opposite of lattice enthalpy

• bonds between ions and water and made-exothermic,enthalpy change of hydration

enthalpy change of solution equation

enthalpy of hydration-lattice enthalpy

enthalpy change of solution enthalpy cycle

factors affecting enthalpy of hydration

• ionic charge

  • ionic radius

how does ionic charge affect enthalpy of hydration

• ions with a greater charge have a greater enthalpy of hydration

• because ions with a higher charge are better at attracting water molecules than those with lower charges

• more energy is released when the bonds are made giving them a more exothermic enthalpy of hydration

how does ionic radius affect enthalpy of hydration

• smaller ions have greater enthalpy of hydration

• as smaller ions have a higher charge density than bigger ions

• they attract water molecules better and have more exothermic enthalpy of hydration

is lattice enthalpy endo or exothermic

exothermic

bond enthaly

The enthalpy change when 1 mole of a particular covalent bond in the gaseous state is broken.

why is the second and third electron affinities endothermic 

incoming electron is added to an already negative ion so energy is required to overcome the repulsive forces between the incoming electron and negative ion