5.2.2 Enthalpy + Entropy

defiine: enthalpy of atomisation

enthalpy change when 1 mol of gaseous atoms forms from its elements in its standard state under standard condition

endothermic

define: ionisation energy

enthalpy change when 1 electron is removed from 1 mol of gaseous atoms

forming 1 mole of 1+ ions under standard conditions

endothermic

define: electron affinity

enthalpy change when 1 electron (e-) is added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions under standard conditions

1st electron affinity

exothermic

electron is attracted into the outer shell of an atom by the nucleus

2nd electron affinity

endothermic

electron is repelled by the 1- ion

the repulsion needs to be overcome, so the energy needs to be provided

define: lattice enthalpy

enthalpy change when 1 mol of ionic compound is made from its gaseous ions under standard conditions

(ionic bond strength)

exothermic

factors: lattice enthalpy

• charge/attraction

• size

lattice enthalpy is directly proportional to charge, indirectly proportional to size

more -ve lattice enthalpy

smaller ionic radius

greater charge density

stronger electrostatic attraction

lattic enthalpy is more exothermic

more +ve lattice enthalpy

larger ionic radius of

smaller charge density

weaker electrostatic attraction

lattice entalpy is less exothermic

define: enthalpy of hydration

enthalpy change when 1 mol of gaseous ions dissolves in excess water to form 1 mol of aqueous ion under s6tandard conditions

exothermic

define: enthalpy of solution

enthalpy change when 1 mol of solute (s) dissolves in water under standard conditions