Enthalpy and Entropy

Created by

Tom Prior

Cards (24)

Why are solid ionic compounds stable?
Electrostatic attractions between oppositely charged ions means that there is a substantial energy barrier which must be overcome to break down the lattice
What is lattice enthalpy?
The enthalpy change which accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
Will lattice enthalpy be exothermic or endothermic?
It will be exothermic as the enthalpy change will always be negative
How can lattice enthalpy be calculated?
Using a special cycle known as the born-haber cycle
What are the two routes which can be used for the calculation?
Route 1- 3 different processes, formation of gaseous atoms, formation of gaseous ions, lattice formation
Route 2- Converts the elements in their standard states directly to the ionic lattice
What is the standard enthalpy change of formation? 
The enthalpy change which takes place when one mole of compound is formed from its elements in standard states under standard conditions, with all reactants and products in standard states
What is the standard enthalpy change of atomisation? 
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
Is enthalpy change of atomisation endothermic or exothermic? 
Endothermic as bonds are broken to form gaseous atoms
What is the first ionisation energy? 
The enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ atoms
What is first electron affinity? 
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms
What happens when water is added to giant ionic lattice structures? 
They are able to break up the ionic lattice structure and overcome strong electrostatic attractions between oppositely charged ions
What is the standard enthalpy change of solution? 
The enthalpy change which takes place when one mole of a solute dissolves in a solvent
Why can ionic lattices break apart in water? 
Due to the partial charges in water and the attraction to the oppositely charged ion
How can you determine enthalpy change of solution? 
Use q=mcdeltaT
What is the dissolving process of a ionic lattice? 
The ionic lattice is broken up forming separate gaseous ion, opposite energy change from lattice energy which forms the ionic lattice from gaseous ions
The separate gaseous ions interact with polar water to form hydrated aqueous ions and this is called enthalpy change of hydration
What is route 1 in enthalpy change of solution?
A+D
Lattice enthalpy + enthalpy change of solution
What is route 2 in enthalpy change of solution? 
B+C
Enthalpy change of hydration*2 ~
How do you calculate lattice enthalpy (solution) using both routes? 
A+D= B+C
What properties do ionic compounds tend to have?
High MP and BP
Soluble in polar solvents
Conduct electricity when molten or aqueous
What are the factors affecting lattice enthalpy? 
Effect of ionic size (Na->Rb) : ionic radius increases, attraction between ions decreases, lattice energy is less negative, MP decreases
What is the other factoe which affects lattice enthalpy? 
Effect of ionic charge (Na+ and Ca2+): The ionic charge increases, attraction between ions increases, lattice energy becomes more negative and therefore MP increases
Factors effecting hydration? 
Ionic radius increases, Attraction between ion and water molecules decreases, hydration energy is less negative
What is required to dissolve a compound in water?
The attraction between the ions in the ionic lattice, this requires a quantity of energy which is equal to lattice enthalpy.
What happens when the sum of the hydration enthalpies is larger than the magnitude of the lattice enthalpy? 
It should dissolve and be exothermic