Lattice enthalpy and the Born-Haber cycle Flashcards
What causes ions to bond together in an ionic lattice?
Electrostatic attraction between oppositely charged ions
Definition of lattice enthalpy?
The enthalpy change that accompanies the formation of 1 mole of an ionic compound from it’s gaseous ions under standard conditions, always negative as bonds being formed
What’s the standard enthalpy change of formation?
Enthalpy change when one mole of a compound is formed from it’s elements under standard conditions, with all reactants and products in standard states
Definition of first ionisation energy?
Energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form 1 mole of gaseous +1 ions, so produces electron with it
What’s the standard enthalpy change of atomisation?
The enthalpy change that takes place for the formation for one mole of gaseous atoms from the elements in its standard state under standard conditions
Going to be positive as bonds broken
Definition of electron affinity?
The enthalpy change that occurs when one electron is added to each atom ine one mole of gaseous atoms of an element to form one mole of gaseous 1- ions, uses up an electron
Which Electron affinity’s are positive and negative?
1st is exothermic, so negative enthalpy, as electron added, will be attracted to the nucleus
Subsequent ones are endothermic, as negatively charged electron being added to a negatively charged ion, and it’s necessary to overcome repulsion
How to draw a born harbour cycle
So from elements in natural state (0) (enthalpy on y axis) you want to atomise the metal and then the gas, each of these are endothermic so go upwards
You then do all the ionisation energies of metal, going upwards with each one producing an electron
You then do all the electron affinitys of gas, with first one going down
From the elements to ionic compound you have the enthalpy change of formation going down
From gaseous ions to ionic compound you have lattice enthalpy change going downwards
What’s the standard enthalpy change of solution?
The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions
What’s the standard enthalpy change of hydration?
The enthalpy change that takes place when one mole of isolated gaseous is dissolved in water forming one mole of aqueous ions under standard conditions
What is entropy?
Dispersal of energy and disorder within the chemicals making up the chemical system
symbol “s”, units are J K^-1 mol^-1
Orders of states in terms of entropy (lowest to highest)?
Solid-liquid-gas-plasma
How do you calculate entropy change?
ΔS = ΣS products - ΣSreactants
How to calculate gibbs free energy?
Gibbs free energy = Enthalpy change - ( kelvin x entropy change)
Entropy change must be divided by 1000 to get it in KJ
What does the value of gibbs free energy represent?
If it is negative the reaction can occur
