Thermodynamics
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What do Born Haber cycles do?
They allow enthalpy changes to be determined which cannot be measured directly.
What substances are lattice enthalpies used for?
Ionic substances
What is the definition of the lattice dissociation enthalpy?
The energy required to break apart an ionic lattice into its constituent ions in a gaseous state and under standard conditions.
What is the definition of lattice formation enthalpy?
The energy required to form an ionic lattice from its constituent ions in a gaseous state and under standard conditions.
What is the definition of enthalpy of electron affinity?
The enthalpy change when one mole of electrons is added to a mole of gaseous atoms under standard conditions.
What is the definition of atomisation enthalpy?
The energy required for the formation of a mole of gaseous atoms under standard conditions.
What is the definition of enthalpy of solution?
The enthalpy change when one mole of ionic solid is dissolved in water to infinite dilution so that the ions no longer interact under standard conditions.
What is the definition of enthalpy of hydration?
The enthalpy change when one mole of gaseous ions is dissolved in water to form one mole of aqueous ions under standard conditions.
Why is enthalpy of hydration mostly negative?
Water has a slightly positive region that naturally attracts slight negative regions.
What does the perfect ionic model suggest?
1) All the ions are perfectly spherical. 2) The ions display no covalent character.
When does covalent character occur?
It appears in ions when two joined ions have varying sizes/charges meaning the distribution of charge is not even.
What is entropy (ΔS)?
A measure of disorder.
What causes a greater entropy value?
As temperature increases, entropy increases. The more disordered a substance is.
Why does entropy value increase when temperature increases?
Particles gain energy and move further apart - they become more disordered.
Out of solids, liquids and gases, what has the greatest entropy?
Gases
When a substance melts or evaporates, does entropy decrease or increase?
Increases.
Why is the entropy change of vaporisation much greater than the entropy change of fusion?
A gas is more disordered than a liquid or solid.
What is entropy change measured in?
J K^-1 mol^-1.
How to calculate entropy change?
Products - Reactants
What is meant by a positive entropy value?
Disorder increases
Gibbs-Free Energy equation?
ΔG = ΔH - TΔS
What is ΔG measured in?
kJ mol^-1
What equation does the Gibbs-Free energy equate to?
y = mx + c
When drawing a graph of Gibbs-Free energy, what is on the x and y axis?
ΔG on the y axis and ΔS on the x axis.