lattice enthalpy Flashcards
what structures do ionic compounds form
giant ionic lattices
what is lattice enthalpy
the enthalpy change when one mole of a solid ionic lattice is formed from its gaseous ions under standard conditions
what are standard conditions
25 degrees celcius
100kPa
what is the standard lattice enthalpy a measure of
ionic bond strength
what does it mean if a lattice enthalpy is more exothermic
the more negative the lattice enthalpy, the stronger the ionic bonds
what two factors affect lattice enthalpy
ionic charge + ionic radius
how does ionic charge affect lattice enthalpy
the higher the charge on the ions, the more energy that is released when an ionic compound forms due to stronger electrostatic attractions between the ions
what processes are involved in a born haber cycle
- lattice enthalpy
- enthalpy of formation
- enthalpy of atomisation
- ionisation energy
- electron affinity
why is the enthalpy change of atomisation endothermic
requires energy to break the bonds holding the atoms together in a molecule
why is the enthalpy change of formation exothermic
forming bonds between elements to form an ionic compound
why is ionisation energy endothermic
energy is required to break the attraction between the negative electrons and positive nucleus
why is the first electron affinity exothermic, but the second endothermic
first electron affinity is exothermic because energy is released when the nucleus attracts an electron
second electron affinity is endothermic as it requires energy to add a negative electron to an already negative ion which experiences repulsion
what processes are involved in an enthalpy of solution cycle
- lattice enthalpy
- hydration enthalpy
- solution enthalpy
why is hydration enthalpy endothermic
breaking bonds to form aqueous ions
why can solution enthalpy be exothermic or endothermic
exothermic when the sum of the hydration enthalpies > lattice enthalpy
endothermic when lattice enthalpy > hydration enthalpies
what processes happen in solution calculations
- dissolve ionic compounds to form its gaseous ions
- bonds form between gaseous ions and water
why do bonds form between the ions and water molecules
oxygen is very electronegative, so it can pull the bonding electrons from the ions towards itself to create a dipole
how does ionic charge effect enthalpy of solution
higher charged ions are better at attracting water molecules so the electrostatic attractions between the ions and water is greater therefore more energy is released when bonds are made
how does ionic radius affect enthalpy of solution
smaller ions have a higher charge density and can attract water molecules better so stronger electrostatic attrcations
