AQA A level Chemistry 3.1.8 –
Thermodynamics Already Passed
What are standard conditions? ✔✔298K/25°C
100kPa/1 atm
1 moldm-3
Enthalpy change of formation ✔✔The enthalpy change when 1 mole of a compound is formed
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AQA A level Chemistry 3.1.8 –
Thermodynamics Already Passed
What are standard conditions? ✔✔298K/25°C
100kPa/1 atm
1 moldm-3
Enthalpy change of formation ✔✔The enthalpy change when 1 mole of a compound is formed
from its constituent elements under standard conditions, with all reactants and products in their
standard states.
Enthalpy change of combustion ✔✔The enthalpy change when 1 mole of a substance is burned
completely in oxygen.
Enthalpy change of atomisation ✔✔The enthalpy change that accompanies the formation of 1
mole of gaseous atoms from the element in its standard state.
First ionisation enthalpy ✔✔The enthalpy change when 1 mole of gaseous atoms loses 1 electron
per atom to form 1 mole of gaseous 1+ ions.
Second ionisation enthalpy ✔✔The enthalpy change when 1 mole of gaseous 1+ ions loses 1
electron per atom to form 1 mole of gaseous 2+ ions.
First electron affinity ✔✔The enthalpy change when 1 mole gaseous atoms gains 1 electron per
atom to form 1 mole of gaseous 1- ions.
Second electron affinity ✔✔The enthalpy change when 1 mole of gaseous 1- ions gains 1
electron per atom to form 1 mole of gaseous 2- ions.
Mean bond enthalpy ✔✔The enthalpy change when 1 mole of gaseous molecules each breaks a
covalent bond to form 2 gaseous ions or free radicals.
Lattice enthalpy of formation ✔✔The enthalpy change when 1 mole of a solid ionic compound is
formed from its gaseous ions.
Lattice enthalpy of dissociation ✔✔The enthalpy change when 1 mole of a solid ionic compound
dissociates into its gaseous ions.
Enthalpy of hydration ✔✔The enthalpy change when 1 mole of gaseous ions dissolves
completely in water.
Enthalpy of solution ✔✔The enthalpy change when 1 mole of an ionic solid dissolves in enough
solvent to ensure that the dissolved ions are well separated and do not interact with one another.
Enthalpy of vaporisation ✔✔The enthalpy change when 1 mole of a liquid evaporates to form 1
mole of a gas.
Enthalpy of sublimation ✔✔The enthalpy change when 1 mole of a solid sublimes to form 1
mole of a gas.
Why are ionisation enthalpies always positive (endothermic)? ✔✔Energy needs to be put in to
pull an electron away from the nucleus to overcome the electrostatic attraction.
Why are first electron affinities always negative (exothermic)? ✔✔Energy is given out when an
electron is attracted to the positively charged nucleus.
Why are second electron affinities and onwards always positive (endothermic)? ✔✔Energy
needs to be put in to overcome the repulsion between an electron and a negatively charged ion.
As the charge of ions increases, the lattice enthalpy... ✔✔Increases.
As the ionic radius increases, the lattice enthalpy... ✔✔Decreases.
If there is "good agreement" between the experimental value (Born-Haber Cycle) and the
electrostatic attraction theory (Perfect Ion Theory) then the bonding is... ✔✔Pure ionic bonding.
If there is "significant difference" between the experimental value (Born-Haber Cycle) and the
electrostatic attraction theory (Perfect Ion Theory) then the bonding is... ✔✔Ionic bonding with
some covalent character.
How much is a significant difference in the perfect ion theory? ✔✔Over 7%.
As charge of CATION (+) increases, covalent character... ✔✔Increases.
As ionic radius of CATION (+) increases, covalent character... ✔✔Decreases.
As charge of ANION (-) increases, covalent character... ✔✔Increases.
As ionic radius of ANION (+) increases, covalent character... ✔✔Increases.
What is the symbol for entropy and what is it measured in? ✔✔S
JK⁻¹mol⁻¹
When the number of molecules increases, entropy... ✔✔Increases.
When the temperature increases, entropy... ✔✔Increases.
Exothermic reactions are _________ likely to happen. ✔✔More
Endothermic reactions are _________ likely to happen. ✔✔Less
Why are exothermic reactions more likely to happen, and endothermic reactions less likely to
happen? ✔✔The universe favours lower enthalpies, so reactions that result in a lower enthalpy
are favoured over reactions that result in a higher enthalpy.
What is the symbol for Gibb's free energy and what is it measured in? ✔✔G
kKmol-1
If a process has ΔG ≤0 then it is... ✔✔Feasible.
If a process has ΔG >0 then it is... ✔✔Not feasible.
Gibb's free energy equation ✔✔ΔG = ΔH - T x ΔS
ΔS must ÷ 1000 to be in kJK⁻¹mol⁻¹
An ENDOthermic reaction with an INCREASE in entropy is... ✔✔Feasible ABOVE a critical
temperature.
An ENDOthermic reaction with an DECREASE in entropy is... ✔✔Never feasible.
An EXOthermic reaction with an INCREASE in entropy is... ✔✔Always feasible.
An EXOthermic reaction with an DECREASE in entropy is... ✔✔Feasible BELOW a critical
temperature.
At 0K the Gibb's free energy equation is ✔✔ΔG = ΔH
At the critical temperature, the Gibb's free energy equation is ✔✔Tc = ΔH
ΔS
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