A2- Born-Haber Flashcards
What is meant by the term ‘enthalpy change of hydration’?
the enthalpy change when one mole of aqueous ions is formed from one mole of gaseous ions
What is the definition of ‘enthalpy of lattice formation’?
the enthalpy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions
Why is enthalpy lattice of formation exothermic?
because it is equal to the formation of an electrostatic force between oppositely charged ions (ionic bond)
Write an equation equal to the lattice formation enthalpy of calcium fluoride
Ca2+(g) + 2F-(g) –> CaF2(s)
What 2 factors impact the size/strength of the enthalpy change of lattice formation?
- size of the ions (larger ions have weaker forces)
- charge of the ions (higher charges = stronger forces)
The lattice enthalpy of sodium chloride is -787 kJ mol -1 . Predict a value for the enthalpy change of lattice dissociation for sodium chloride. Explain your answer.
+ 787 kJ mol -1 . Lattice dissociation is the opposite enthalpy change of lattice formation and is endothermic due to breaking and ionic bond between Na + and Cl - ions
What is meant by the term ‘enthalpy change of atomisation’?
the enthalpy change when one mole of an element in its standard state is converted to gaseous atoms
What is meant by the term ‘enthalpy change of bond dissociation’?
the enthalpy change when one mole of covalent bonds dissociate/break forming gaseous molecules.
What is meant by the term ‘1st ionisation enthalpy’?
1 st ionisation enthalpy - The enthalpy change when one mole of gaseous atoms is converted into one mole of
gaseous ions with a 1+ charge and one mole of electrons
Why is 1st ionisation enthalpy an endothermic change?
because the electrostatic force of attraction between nucleus and electron is broken
Describe and explain the trend in ionisation enthalpy going down a group
Ionisation enthalpy increases down a group because atoms become larger with more electron shielding, therefore the electrostatic force between nucleus and outer electron shell becomes weaker and it is easier to remove an electron.
Describe and explain the trend in ionisation enthalpy going across a period
Ionisation enthalpy increases across a period because electron shielding remains constant, but nuclear charge increases creating a stronger electrostatic force between nucleus and outer electron shell making it harder to lose and electron.
What is meant by the term ‘1st electron affinity’?
The enthalpy change when one mole of electrons is added to one mole of
gaseous atoms is converted into one mole of gaseous ions with a charge of 1 –
What type of reaction is 1st electron affinity? why?
exothermic, because an electrostatic force (bond) is formed between nucleus and an
electron
What type of reaction is 2nd electron affinity?
Endothermic
A bond is formed between nucleus and an electron, however there is a lot of repulsion to be overcome as and electron is being added to a negatively charged ion
