5.2 Energy Flashcards
Define lattice enthalpy
enthalpy change associated with the formation of one mole of an ionic lattice from its gaseous ions under standard conditions K+(g) +Cl- –> KCl(s)
Define enthalpy change of formation
The enthalpy change associated with the formation of one mole of a compound from its constituent elements in their standard conditions
How do lattice enthalpy values indicated the relative strength of ionic bonds
More exothermic lattice enthalpy values mean stronger ionic bonds and higher melting and boiling point
It also indicates smaller ions and larger charges
What can we use to measure lattice enthalpy
Born - Haber cycles because we can’t measure lattice enthalpy directly
What are the key features of a born haber cycle
continuous cycle
includes on step that shows the formation of one mole of the solid ionic lattice from the gaseous atoms
the remaining steps show intermediate changes
the lattice enthalpy can be calculated by applying hess’ law
Define the enthalpy change of atomisation
The enthalpy change associated when one mole of gaseous atoms is formed from its element in its standard state
K(s) –> K(g)
Define first ionisation energy
When one mole of gaseous 1+ ions is formed from its gaseous atoms
K (g)- e –> K+(g)
Define second ionisation energy
When one mole of gaseous 2+ ions are formed from one mole of gaseous 1+ ions
Mg+(g) - e- –> Mg2+(g)
Define the first electron affinity
when one mole of gaseous 1- ions is formed from gaseous atoms
Cl (g)+ e- –> Cl- (g)
Define second electron affinity
When one mole of gaseous 2- ions is formed from one mole of gaseous 1- ions
Describe the steps in a born haber cycle to determine lattice enthalpy of sodium chloride
atomisation of sodium
atomisation of chlorine
ionisation of sodium
electron affinity of chlorine
What happens when a solid dissolves
The ionic lattice breaks down
the free ions become a part of the solution (hydration )
Define the standard enthalpy of solution
The enthalpy change that take place when one mole of a solute is completely dissolved in water under standard conditions
KCl (s) = + aq –> K+ (aq) + Cl- (aq)
What is the enthalpy change associated with the breakdown of an ionic lattice
Lattice enthalpy of dissociation
How do lattice enthalpies differ energetically
Association is exothermic
Dissociation is endothermic
What dictates the size of the lattice enthalpy
the size of the ions involved
the charge on the ions
How does ionic radius affect lattice enthalpy
smaller ions can get closer together and will attract one another more strongly and give rise to a more exothermic lattice enthalpy values
How does ionic charge affect lattice enthalpy
Ions with higher charges cause greater electrostatic attraction and in turn more exothermic lattice enthalpy values
hat ions have the most negative lattice enthalpy values
The smallest most highly charged ions will give rise to the most exothermic lattice enthalpies as they can pack closer to the oppositely charged ions with a higher attraction
Define the standard enthalpy of hydration
The enthalpy change that takes place when dissolving one mole of gaseous ions in water under standard conditions
K+ (g) –> K+(aq)
What occurs during hydration
The positive ions will be attracted to the slightly negative oxygen
The negative ions will be attracted to the slightly positive hydrogen
the water molecules will completely surround the ions
What kind of process is hydration
Exothermic
What dictates enthalpy of hydration
Ionic radius
ionic charge