lattice enthalpy Flashcards
define lattice enthalpy
It is the formation of 1 mole of a solid ionic lattice from its constituent gaseous ions under standard conditions
what does a more exothermic lattice enthalpy mean?
more exothermic = stronger ionic bonds
why is it not possible to measure lattice enthalpy directly?
it is not possible to form 1 mole of ionic solid from its gaseous ions
define enthalpy change of solution
enthalpy change that takes place when 1 mole of a solute is completely dissolved in water under standard conditions
define enthalpy change of hydration
the enthalpy change that takes place when dissolving one mole of gaseous ions in water
what are the factors that impact the size of lattice enthalpy
- the size of ions involved
- charges on the ions
- ionic bond strength
explain which ions have more negative lattice enthalpy values: smaller or larger ions?
- smaller ions
- they have a stronger nuclear attraction
- they have a greater charge density
describe hydration
- ionic lattice is broken and the ions become part of the solution
- positive ions get attracted towards slightly negative oxygen and negative ions get attracted towards slightly positive hydrogen
what are the factors that impact the magnitude of the enthalpy of hydration
- the size of the ion
- charge of the ions
explain why the second ionisation energy of an element may be more exothermic than its first ionisation energy
- the ion is smaller than the atom
- the electrons are closer to the nucleus and feel a bigger nuclear attraction
suggest why the second electron affinity of an element may be positive
- both the ion and the electron are negative
- energy is required to overcome the repulsion
what type of process is lattice association (formation)
exothermic
what type of process is lattice dissociation
endothermic
what is the ΔH of formation
the enthalpy change where 1 mole of a compound is formed from its constituent elements
what is the ΔH of formation?
the enthalpy change where 1 mole of a compound is formed from its constituent elements
what is the enthalpy change of ionisation
the energy change where 1 mole of electrons are removed from 1 mole of gaseous atoms/ions
what is the ΔH of atomisation
the enthalpy change where 1 mole of an element in its standard state is atomised to 1 mole of gaseous atoms
what is the bond enthalpy
the energy change where 1 mole of a bond type in the gaseous state is broken to give separate atoms
what is the ΔH of electron affinity
the energy change where an electron is added to an atom in the gaseous state
what is the equation for calculating the enthalpy change of the solution?
ΔH solution = ΔH lattice dissociation + ΔH hydration
what does it mean if the ΔH of the solution is positive?
- less likely to be more soluble
what does it mean if the ΔH of the solution is negative
- more likely to be more soluble
