22 Enthalpy and Entropy Flashcards
Lattice enthalpy
The enthalpy change that accompanies the formation of 1 mole of an ionic compound from its gaseous ions under standard conditions.
Standard enthalpy change of atomisation
Enthalpy change that takes place when 1 mole of gaseous atoms forms from the element in its standard state.
First ionisation energy
Enthalpy change required to remove one electron from each atom in 1 mole of gaseous atoms to form 1 moles of 1+ gaseous ions.
First electron affinity
Enthalpy change that takes place when one electron is added to each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions.
Standard enthalpy change in solution
Enthalpy change that takes place when 1 mole of solute dissolves in a solvent.
Enthalpy change of hydration
Enthalpy change that takes place when dissolving of 1 mole of gaseous ions in water to form 1 mole of aqueous ions.
What are the factors affecting lattice enthalpy?
Ionic size and ionic charge.
Entropy
The dispersal of energy within the chemicals making up the system. Greater entropy = greater disorder.
What happens to the entropy when the state changes from solid to liquid to gas?
Entropy increases as the arrangement of particles becomes more random.
Standard entropy
Entropy of 1 mole of a substance under standard conditions.
What is the Gibbs’ equation?
ΔG = ΔH - TΔS
For a reaction to be feasible, there must be…
A decrease in free energy i.e. ΔG < 0
How do you find the minimum temperature at which a reaction is feasible?
Calculate ΔS. Equate Gibbs’ equation to zero and rearrange to find T.
What are the limitations of predictions about feasibility?
ΔG does not take kinetics or the rate of reaction into account.
Some reactions can negative ΔG and not happen.
