22.1 Lattice enthalpy Flashcards
What is lattice enthalpy?
A measure of strength of ionic bonding in a giant ionic lattice
Definition of lattice enthalpy
The enthalpy change for the formation of 1 mole of an ionic compound (s) from its gaseous ions under standard conditions
What type of energy change is lattice enthalpy?
Exothermic change (-kJmol-1)
What are the units for lattice enthalpy?
-kJmol-1
How is lattice enthalpy measured an why?
Using Born-Haber cycles, as lattice enthalpy cannot be measured directly and must be calculated in directing using known energy changes
What are the two routes for changing elements in their standard states into an ionic lattice
Route 1 -
-formation of gaseous atoms
-formation of gaseous ions
-lattice formation (lattice enthalpy)
Route 2 -
elements in standard states directly to the ionic lattice (enthalpy change of formation)
Definition of enthalpy change of formation (ΔfH)
The enthalpy change that takes place when 1 mole of compound is formed from its elements under standard conditions, with all reactants and products in their standard states
Definition of enthalpy change of atomisation (ΔatH)
The enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
What type of energy change is the enthalpy change of atomisation?
Endothermic (positive), as bonds are broken to form gaseous ions
Definition of first ionisation energy (ΔIEH)
The enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to from one mole of gaseous 1+ ions
What type of energy change is first ionisation energy?
Endothermic because energy is required to overcome the attraction between a negative electron and positive nucleus
What is the difference between ionisation energy and electron affinity?
-Electron affinity is the opposite of ionisation energy
-Electron affinity measures the energy to gain electrons, ionisation energy measures the energy change to loose electrons
Definition of first electron affinity (ΔEAH)
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
What energy change is first electron affinity?
Exothermic, electrons being added is attracted towards the nucleus
What is the equation to show the enthalpy change of formation (ΔfH) of sodium chloride?
What type of energy change is 2nd electron affinity?
Endothermic (positive), as a second electron is gained by a negative ion, which repels the electron away. So energy must be put in to force the negatively-charged electron onto the negative ion
