Lattice Enthalpy and Born Haber Cycles Flashcards
Define standard lattice enthalpy.
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions.
It’s a measure of ionic bond strength.
How does ionic charge affect lattice enthalpy?
The higher the charge on the ions, the more energy is released when an ionic lattice forms.
More energy released means that the lattice enthalpy will be more negative.
How does size affect lattice enthalpy?
The smaller the ionic radii of the ions involved, the more exothermic (more negative) the lattice enthalpy. Smaller ions attract more strongly because their charge density is higher.
What does Hess’s law state?
The total enthalpy change of a reaction is always the same, no matter which route is taken.
Enthalpy change of formation ΔHfΘ
The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
Na(s) + ½ Cl2 (g) -> NaCl(s)
Standard enthalpy of atomization ΔatHΘ
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard state.
½ Cl2 (g) → Cl (g)
First ionisation energy definition.
The energy required to remove the outermost electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+.
Second ionisation energy
The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.
First electron affinity
The enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to in one mole of gaseous 1- ions
Cl (g) + e- → Cl- (g)
Second electron affinity
The enthalpy change accompanying the addition of one electron to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions
What is lattice enthalpy?
Lattice enthalpy is a measure of the strength of the forces between the ions in an ionic solid.
Suggest why the second electron affinity of oxygen is positive.
“oxide” ion and electron are both negative hence energy is required to overcome repulsion
Enthalpy change of solution
The enthalpy change when 1 mole of solute is dissolved in sufficient solvent than no further enthalpy change occurs on further dilution.
What two things happen when a solid ionic lattice dissolves in water.
1) The bonds between the ions break- this is endothermic. The enthalpy change is the opposite of the lattice enthalpy.
2) Bonds between the ions and water are made- this is exothermic. The enthalpy change here is called the enthalpy of hydration.
How does ionic charge affect enthalpy of hydration?
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.
