AQA A level Chemistry 3.1.8 - Thermodynamics
What are standard conditions?
298K/25°C 100kPa/1 atm 1 moldm-3
An EXOthermic reaction with an INCREASE in entropy is...
Always feasible.
As ionic radius of CATION (+) increases, covalent character...
Decreases.
As the ionic radius increases, the lattice enthalpy...
Decreases.
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.
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.
An ENDOthermic reaction with an INCREASE in entropy is...
Feasible ABOVE a critical temperature.
An EXOthermic reaction with an DECREASE in entropy is...
Feasible BELOW a critical temperature.
If a process has ΔG ≤0 then it is...
Feasible.
What is the symbol for Gibb's free energy and what is it measured in?
G kKmol-1
As charge of ANION (-) increases, covalent character...
Increases.
As charge of CATION (+) increases, covalent character...
Increases.
As ionic radius of ANION (+) increases, covalent character...
Increases.
As the charge of ions increases, the lattice enthalpy...
Increases.
When the number of molecules increases, entropy...
Increases.
When the temperature increases, entropy...
Increases.
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.
Endothermic reactions are _________ likely to happen.
Less
Exothermic reactions are _________ likely to happen.
More
An ENDOthermic reaction with an DECREASE in entropy is...
Never feasible.
If a process has ΔG >0 then it is...
Not feasible.
How much is a significant difference in the perfect ion theory?
Over 7%.
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.
What is the symbol for entropy and what is it measured in?
S JK⁻¹mol⁻¹
At the critical temperature, the Gibb's free energy equation is
Tc = ΔH ΔS
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 electron affinity
The enthalpy change when 1 mole gaseous atoms gains 1 electron per atom to form 1 mole of gaseous 1- ions.
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 of vaporisation
The enthalpy change when 1 mole of a liquid evaporates to form 1 mole of a gas.
Lattice enthalpy of dissociation
The enthalpy change when 1 mole of a solid ionic compound dissociates into its gaseous ions.
Lattice enthalpy of formation
The enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions.
Enthalpy of sublimation
The enthalpy change when 1 mole of a solid sublimes to form 1 mole of a gas.
Enthalpy change of combustion
The enthalpy change when 1 mole of a substance is burned completely in oxygen.
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.
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.
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.
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.
Enthalpy of hydration
The enthalpy change when 1 mole of gaseous ions dissolves completely in water.
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.
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.
At 0K the Gibb's free energy equation is
ΔG = ΔH
Gibb's free energy equation
ΔG = ΔH - T x ΔS ΔS must ÷ 1000 to be in kJK⁻¹mol⁻¹
