chapter 22- enthalpy and entropy

why are ionic compounds so stable

the strength of the ionic bonds, electrostatic attraction between oppositely charged ions in the ionic lattice structure

what is lattice enthalpy

the enthalpy change that accompanies the formation of 1 mole of an ionic compound from it’s gaseous ions under standard conditions

what is lattice enthalpy used to measure

the strength of an ionic bond

what are 3 processes in route 1 of the borne-harber cycle

• formation of gaseous atoms

• formation of gaseous ions

• lattice formation

how do you form gaseous atoms for the borne-harber cycle

changing the elements in their standard states into gas atoms

• endothermic (bond breaking)

how do you form gaseous ions for the borne-harber cycle

changing gaseous atoms into positive and negative gaseous ions

• endothermic change

how do you form a lattice in the borne-harber cycle

changing the gasesous ions into a solid ionic lattice

• exothermic change

what is route 2 of the borne-harber cycle

converting elements in their standard states directly to the ionic lattice (enthalpy of formation exothermic)

standard enthalpy change of formation

the enthalpy change that takes place when one mole of a compound is formed from its constituent elements under standard conditions

standard enthalpy change of atomisation

the enthalpy change that takes place for the formation of 1 mole of gaseous atoms from the element in it standard state under standard conditions

1st ionisation energy

the enthalpy change required to remove 1 electron from each atom in 1 mole of gaseous atoms in order to form 1 mole of gaseous 1+ ions

1st electron affinity

the enthalpy change required to add 1 electron to each atom in 1 mole of gaseous atoms in order to form 1 mole of gaseous 1- ions

steps of a route 1 borne harber cycle

• enthalpy change of atomisation for element 1

• enthalpy change of atomisation for element 2

• first ionisation energy for the cation

• first electron affinity for the anion

• lattice enthalpy of the ionic compound

steps for route 2 of the borne-harber cycle

• enthalpy change of formation of the ionic compound

how would you write 1st electron affinity

X_(g) + e^- —> X^- (g)

how would you write second electron affinity

X^-(g) + e^- —> X^2-_(g)

why is the second electron affinity endothermic

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 e^- into the negative ion