Born-Haber Cycles + Gibbs Free Energy + Entropy Flashcards
enthalpy of formation definition
the energy required to form an ionic lattice from its constituent ions in a gaseous state under standard conditions
ionisation energy definition
the energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of an ion.
enthalpy of atomisation definition
the energy required for the formation of one mole of gaseous atoms under standard conditions
bond enthalpy definition
the heat energy needed to break one mole of the bond under standard conditions
electron affinity definition
the enthalpy change when one mole of electrons is added to one mole of gaseous atoms under standard conditons
Example of a Born Haber Cycle
up arrows = positive number
down arrows = negative number
compare lattice enthalpies from Born–Haber cycles with those from calculations based on a perfect ionic model to provide evidence for covalent character in ionic compounds.
The perfect ionic model:
- are perfectly spherical
- displays no covalent character
covalent character occurs when two joined ions have varying sizes/charges therefore the distribution is not even.
enthalpy of hydration definition
the enthalpy change when one mole of gaseous ions is dissolved in water to form one mole of aqueous ions under standard conditions.
Example of the cycle + what is the equation for enthalpy of solution
What is entropy and which state of molecules has the greatest entropy and why?
Entropy is a measure of disorder.
Solid<Liquid<Gas
Gas is most entropic because the particles are more spread apart.
Entropy increases as temp increases so particles gain energy and move further away.
What are the equations for gibbs free energy (feasibility), entropy and enthalpy and give their units.
∆G = ∆H - T∆S
∆G = kJ
∆H = kJ
∆S = J (must be divided by 1000 to make kJ)
For a reaction to be feasible, the value of ∆G must be zero or negative.
entropy equation:
products - reactants
enthalpy equation:
bonds broken - bonds made
Equation for the temperature range at which the reaction is feasible.
rearrange gibbs free energy
so:
T= ∆H / (∆S divided by 1000)
How does the free gibbs energy equation relate to the y=mx+c equation
y = m x + c
∆G = -∆S T + ∆H
-∆S = gradient (must be x1000 bc ∆S is in Joules, must be in kJ)
eg if gradient = -2, then ∆S would be 2000
∆S gradient = y/x x 1000
∆H = y intercept
Tips and tricks for gibbs free energy graph
negative gradient = positive ∆S
positive gradient = negative ∆S
why couldnt reactions happen at too hot or too cold temperatures?
too hot: reactants + products would decompose
too cold: they would be in different states
