energetics 2 p1 Flashcards
what is Hess’ Law?
the enthalpy change for a reaction is independent of the route taken
standard enthalpy of atomisation
enthalpy change when one mole of gaseous atoms is formed from a compound in its standard state in standard conditions
1/2I2(g) –> I(g)
first ionisation energy
enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Li(g) –> Li+(g) + e-
second ionisation energy
enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
Mg+(g) –> Mg2+(g) + e-
first electron affinity
enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous 1- ions
Cl(g) + e- –> Cl-(g)
second electron affinity
enthalpy change when one mole of gaseous 1- ions gains one mole of electrons to form one mole of gaseous 2- ions
O-(g) + e- –> O2-(g)
lattice enthalpy of formation
enthalpy change when one mole of solid ionic lattice is formed from its constituent gaseous ions
Na+(g) + Cl-(g) –> NaCl(s)
enthalpy of hydration
enthalpy change when one mole of gaseous ions become hydrated/dissolved in water to infinite dilution (water molecules totally surround the ion)
Na+(g) –> Na+(aq)
enthalpy of solution
enthalpy change when one mole of solute dissolves completely in a solvent to infinite dilution
NaCl(s) –> Na+(aq) + Cl-(aq)
mean bond dissociation enthalpy
enthalpy change when one mole of (a certain type of) covalent bond is broken, with all species in the gaseous state
Br2(g) –> 2Br(g)
what is a Born-Haber cycle?
thermochemical cycle showing all the enthalpy changes involved in the formation of an ionic compound. start with elements in their standard states (enthalpy of 0)
Born Haber cycle - up arrows and down arrows
up - atomisation, ionisation
down - formation, affinity, lattice formation
what factors affect the lattice enthalpy of an ionic compound?
size of ions, charge on ions
how can you increase the lattice enthalpy of a compound? why does this increase it?
smaller ions, since the charge centres will be closer together
increased charge, since there will be a greater electrostatic force of attraction between the oppositely charged ions
increasing charge on the anion has a smaller affect since increasing anion charge also increases ionic size
how can Born-Haber cycles be used to see if compounds could theoretically exist?
use known data to predict certain values of theoretical compounds then see if these compounds would be thermodynamically stable
used to predict the first noble gas containing compound