Year 13 AQA A-Level Chemistry Quick Revision
Thermodynamics
Standard state = 1 mole, 100kPa, 298K
Enthalpy change of formation- enthalpy change when 1 mole of a compound is formed from
its constituent elements under standard conditions with all elements in their standard states.
Enthalpy change of dissociation- Enthalpy change when 1 mole of covalent bonds is broken
in the gaseous state
Enthalpy change of combustion- Enthalpy change when one mole of a compound is burned
completely in oxygen under standard conditions, and with everything in its standard state.
1st Ea- Enthalpy change when 1 mole of gaseous 1- ions are made from 1 mole of gaseous
atoms
Lattice enthalpy of dissociation- Enthalpy change when 1 mole of ionic solid compound is
dissociated into its gaseous ions under standard conditions
Lattice enthalpy of formation- Enthalpy change when 1 mole of a solid ionic compound is
formed from it's gaseous ions under standard conditions
Enthalpy of atomisation- Enthalpy change when 1 mole of gaseous atoms are made from an
element in their standard state
2nd Ie- Enthalpy change when 1 mole of gaseous 1+ ions lose 1 mole of electrons to form 1
mole of gaseous 2+ ions.
2nd Ea- Enthalpy change when 1 mole of gaseous 2- ions are made from 1 mole of gaseous
1- ions when they gain 1 mole of e-
1st Ie- Enthalpy change when 1 mole of gaseous atoms lose 1 mole of electrons to form 1
mole of gaseous 1+ ions.
Enthalpy change of solution- Enthalpy change when 1 mole of an ionic substance is dissolved
in the minimum amount of solvent to ensure that no further enthalpy change is observed
during dilution.
Enthalpy change of hydration- Enthalpy change when one mole of gaseous ions is dissolved
in water to form one mole of aqueous ions under standard conditions.
Mean bond enthalpy- Enthalpy change when one mole of gaseous covalent bonds are broken
averaged over a range of different compounds.
, Theoretical and Experimental Lattice enthalpies
-Theoretical lattice enthalpies can be calculated assuming a perfectly ionic model
-Perfectly ionic model is assuming ions are perfectly spherical and that charge is evenly
distributed in this sphere (point charges) which means charge concentrated at centre.
-Most of the time the positive ion distorts the charge distribution in the negative ion, we say
the positive ion polarises the negative ion.
-The more polarisation the more covalent character there will be.
-This tells us that the compound being experimented on doesn't follow perfect ionic model
and has some covalent characteristics.
Normally experimental value shows a higher lattice enthalpy showing covalent
character
Enthalpy of solution = Enthalpy of dissociation + Enthalpy of hydration.
Entropy = measure of disorder within a system.
Increasing entropy is energetically favourable and some reactions that are enthalpically
unfavourable can still react if changes in entropy overcome changes in enthalpy.
Remember convert delta H from kJ mol to J mol
Thermodynamics
Standard state = 1 mole, 100kPa, 298K
Enthalpy change of formation- enthalpy change when 1 mole of a compound is formed from
its constituent elements under standard conditions with all elements in their standard states.
Enthalpy change of dissociation- Enthalpy change when 1 mole of covalent bonds is broken
in the gaseous state
Enthalpy change of combustion- Enthalpy change when one mole of a compound is burned
completely in oxygen under standard conditions, and with everything in its standard state.
1st Ea- Enthalpy change when 1 mole of gaseous 1- ions are made from 1 mole of gaseous
atoms
Lattice enthalpy of dissociation- Enthalpy change when 1 mole of ionic solid compound is
dissociated into its gaseous ions under standard conditions
Lattice enthalpy of formation- Enthalpy change when 1 mole of a solid ionic compound is
formed from it's gaseous ions under standard conditions
Enthalpy of atomisation- Enthalpy change when 1 mole of gaseous atoms are made from an
element in their standard state
2nd Ie- Enthalpy change when 1 mole of gaseous 1+ ions lose 1 mole of electrons to form 1
mole of gaseous 2+ ions.
2nd Ea- Enthalpy change when 1 mole of gaseous 2- ions are made from 1 mole of gaseous
1- ions when they gain 1 mole of e-
1st Ie- Enthalpy change when 1 mole of gaseous atoms lose 1 mole of electrons to form 1
mole of gaseous 1+ ions.
Enthalpy change of solution- Enthalpy change when 1 mole of an ionic substance is dissolved
in the minimum amount of solvent to ensure that no further enthalpy change is observed
during dilution.
Enthalpy change of hydration- Enthalpy change when one mole of gaseous ions is dissolved
in water to form one mole of aqueous ions under standard conditions.
Mean bond enthalpy- Enthalpy change when one mole of gaseous covalent bonds are broken
averaged over a range of different compounds.
, Theoretical and Experimental Lattice enthalpies
-Theoretical lattice enthalpies can be calculated assuming a perfectly ionic model
-Perfectly ionic model is assuming ions are perfectly spherical and that charge is evenly
distributed in this sphere (point charges) which means charge concentrated at centre.
-Most of the time the positive ion distorts the charge distribution in the negative ion, we say
the positive ion polarises the negative ion.
-The more polarisation the more covalent character there will be.
-This tells us that the compound being experimented on doesn't follow perfect ionic model
and has some covalent characteristics.
Normally experimental value shows a higher lattice enthalpy showing covalent
character
Enthalpy of solution = Enthalpy of dissociation + Enthalpy of hydration.
Entropy = measure of disorder within a system.
Increasing entropy is energetically favourable and some reactions that are enthalpically
unfavourable can still react if changes in entropy overcome changes in enthalpy.
Remember convert delta H from kJ mol to J mol
