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AQA Chemistry Thermodynamics Q&A
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AQA Chemistry Thermodynamics Q&A Can be used for exam question practice, very useful
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What are standard conditions? 100kPa and 298KWhat is the enthalpy change of formation? The standard enthalpy of formation is the
enthalpy change that occurs when one mole of a substance is formed from its elements under
standard conditions, all reactants and products being in their standard states.
Na(s) +½Cl2(g) --> NaCl (s)
What is the enthalpy of atomisation? The enthalpy of atomisation is the enthalpy change that
occurs when one mole of gaseous atoms is formed from its elements under standard states
½ O2(g) --> O (g)
What is the enthalpy of sublimation? The enthalpy of sublimation is the enthalpy change that
occurs when one mole of solid metal turns one mole of gaseous atoms under standard
conditions. It is numerically the same as the enthalpy of atomisation.
Na(s) --> Na(g)
What is the bond dissociation enthalpy? The bond disassociation enthalpy is the standard
molar enthalpy change that occurs when one mole of a covalent bond is broken into two
gaseous atoms(free radicals)
Cl2 (g) --> 2Cl (g)
CH4 (g) --> CH3 (g)+ H(g)
For diatomic molecules, the Bond Dissociation enthalpy is two times the Enthalpy of
atomisation of that element
What is the first ionisation enthalpy? The first ionisation enthalpy is the enthalpy change that
occurs when one mole of e- is removed from one mole of gaseous atoms to form one mole of
gaseous +1 ions.
What is the second ionisation enthalpy? The second ionisation enthalpy is the enthalpy
change that occurs when one mole of gaseous +1 ions remove one mole of e- to produce one
mole of gaseous +2 ions.
What is the first electron affinity? The first electron affinity is the enthalpy change that
occurs when one mole of gaseous atoms gain one mole of e- to form one mole of gaseous 1-
ions
Why is the First Electron Affinity EXOthermic for atoms that normally form negative ions?
First Electron Affinity is EXOthermic because the ion is more stable than the atom,
and so there is an attraction between the nucleus and the e-, energy is released
What is Second Electron Affinity? Second electron affinity is the enthalpy change when
one mole of gaseous 1- ions gain one electron per ion to produce one mole of gaseous 2- ions
Why is the Second Electron Affinity ENDOthermic? The Second Electron Affinity is
ENDOthermic because it takes energy to overcome the repulsive force between the negative
ion and the e-
What is the Enthalpy of Lattice Formation? The enthalpy of lattice formation is the enthalpy
change that occurs when one mole of an ionic crystal lattice is formed from its constituent
ions in gaseous form
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