Thermodynamics Flashcards
Define ‘enthalpy of formation’
The enthalpy change when 1 mole of compound is made from its elements with everything in its standard states under standard conditions
Ca(s) + C(s) + 1/2 O2 —> CaCO3(s)
Define ‘enthalpy of atomisation’ (sublimation)
The enthalpy change when 1 mole of gaseous atoms is formed from an element in its standard states.
Na(s) –> Na(g)
Define ‘first ionisation enthalpy’
The enthalpy change when 1 mole of gaseous 1+ ions made from 1 mole of gaseous atoms under standard conditions.
Na(g) —> Na+(g) + e-
Define ‘ second ionisation energy’
The enthalpy change when each ion in 1 mole of gaseous 1+ ions loses 1 electron to form 1 mole of gaseous 2+ ions
Na+(g) –> Na2+(g) + e-
Define ‘first electron affinity’
The enthalpy change when 1 mole of gaseous 1- ions made from 1 mole oif gaseous atoms.
Cl(g) + e- —> Cl-(g)
Why is 1st electron affinity EXOthermic?
Ion more stable than the atom
Attraction between nucleus + electron
Define ‘second electron affinity’
The enthalpy change when each atom of 1 mole of gaseous 1- ions gain and electron to form 1 mole of gaseous 2- ions.
O-(g) + e- –> O2-
Why is 2nd electron affinity ENDOthermic?
Takes energy to overcome repulsive force between negative ion and electron.
Define ‘enthalpy of hydration’
The enthalpy change when 1 mole of gaseous ions become aqueous ions (dissolved in water).
Na+(g) —> Na+(aq)
Always gives OUT energy (EXO) –> bonds between ions + water molecules
Define ‘enthalpy of solution’
The enthalpy change when 1 mole of an ionic substance is dissolved in a volume of water large enough to ensure all the ions are separated and do not interact with each other.
MgSO4(s) —> Mg2+(aq) + SO42-(aq)
Define ‘ enthalpy of lattice formation’
The enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions.
Na+(g) + Cl-(g) –> NaCl
Define ‘enthalpy of lattice dissociation’
The enthalpy change when 1 mole of solid ionic compound is dissociated into its gaseous ions under standard conditions.
NaCl(s) —> Na+ + Cl-
Define ‘bond dissociation enthalpy’
The standard molar enthalpy change when 1 mole of a covalent bonds broken under standard conditions producing gaseous fragments.
CH4 —> CH3. + H.
What is the relationship between Bond dissociation enthalpy and enthalpy of atomisation?
In diatomic molecules:
Bond dissociation = 2x atomisation
Why are Born-Haber cycles used?
Lattice enthalpy cannot be determined directly –> calculated indirectly by making use of changes of data available
What do the strength of enthalpy of lattice formation rely depend on?
Size of the ions
Charges of ions
