chem 23: chemical energetics

standard conditions

• 298K

• 100kPa

• 1 mol dm-3 conc

• products and reactants in standard states

standard enthalpy change of atomisation

when one mole of gaseous atoms are formed from the element in its standard state

enthalpy change of hydration

when only mole of gaseous ions dissolve in water

enthalpy change of solution

when one mole of ionic solid dissolves in water

lattice energy/ lattice formation enthalpy

when one mole of a solid ionic lattice is formed from its gaseous ions

lattice dissociation enthalpy

when one mole of an ionic compound breaks down to form its gaseous ions

is gaseous ions form a solid lattice then?

enthalpy change is negative

factors that affect lattice enthalpy

• ionic charge: increases, attractions btwn pos and neg ions increase so more negative lattice formation enthalpy

• ionic radius: decreasing radius, brings neg and pos ions closer so increased attraction so larger and stronger lattice enthalpy

must talk about pos and neg ions, attraction and more stronger negative lattice enthalpy

electron affinity

when one mole of a gaseous ion gain one electron to form one mole of 1- ions

factors that affect electron affinity

• nuclear charge: strongly attracts the electron

• shielding: shielding repels electrons, so less attraction

• atomic radius: big radius means more distance btwn nucleus and electron so less attraction

talk about the electron affinity trend in groups 6 & 7 going down

down the group nuclear charge increases bc of more p+ and so do atomic radius and electron shielding bc increasing number of shells. this leads to less attraction w/ the e- that’s coming bc of repulsion and so a lower electron affinity

what elements in g6 and g7 are exceptions and why

fluorine and oxygen

because they are relatively small and so have a higher density of electrons since it’s so compact causing repulsion with incoming electrons

so have a low electron affinity

second electron affinity

the energy required to add one electron to one mole of gaseous 1- ions to turn it into one mole of 2- gaseous ions

why does 2nd electron affinity energy is required instead of released

bc the first EA happened so the electron will try repel the new one that’s coming in so energy is required

enthalpy change of formation

when one mole of a compound is formed from its elements under standard conditions

ionisation energy

the energy required to remove an electron from one mole of gaseous atoms to form one of of 1+ ions

between electron affinity and ionisation energy which one is for non metals and which one is for metals

electron affinity = non metals and which

IE = metals

born haber cycle steps

• FLAIE

• start with doing the formation and lattice energy (the standard states 1:1 and in ion form)

• then it’s atomisation (gas form and turn any diatomic atom into one)

• then ionisation energy ion + e-

• then the last step is to do electron affinity where they both turn into ions

reaction pathway diagrams