Chapter 17 - Thermodynamics Flashcards
What two definitions can lattice enthalpy have and why can they both be used?
Enthalpy of lattice formation and also enthalpy of lattice dissosciation. They can both be used because it requires the same amount of energy to break the bonds in a lattice as it does to form them
What type of diagram is typically used to calculate lattice enthalpy?
Born-Haber cycles
What other enthalpies are required to construct a complete Born-Haber cycle?
Enthalpy of formation
Enthalpy of atomisation
Ionisation energy
Electron Affinity
What is enthalpy of atomisation?
The energy change when one mole of gaseous atoms are formed from its element at standard conditions and standard state
What is electron affinity?
The amount of energy required for one mole of a gaseous substance to gain ond mole of electrons
M(g) + e- -> M-(g)
Why will thelattice enthalpy calculated from a Born-Haber cycle be different to the experimental value?
Because the Born-Haber cycle will not take covalent character into consideration and only works off of the perfect ionic model, whereas in reality many lattices experience some covalent character
Define enthalpy of solution:
The enthalpy change when one mole of solute dissolves completely (in enough solvent to be able to become far enough away so that the ions do not interact with each other anymore)
Define enthalpy of hydration
The enthalpy change when water molecules surround one mole of aqueous ions
What other data is required to use a cycle to calculate the enthalpy of solution for a lattice?
The enthalpy of lattice dissosciation
The enthalpies of hydration
What is “feasible change”. What is not enough to explain feasible change
Feasible change is a reaction which is possible to happen, and does so to increase the stability of the system. Enthalpy change by itself is not enough data to explain this by itself, and entropy change is also required
What is entropy, and what does nature prefer?
Entropy is a measure of the state of disorder of a system, and nature typically prefers higher states of entropy (more disordered systems)
Which equation is able to link entropy and enthalpy in a feasible reaction?
DeltaG (Gibb’s Free Energy) = DeltaH - T(K) X DeltaS(entropy)
Reactions are feasible when Gibb’s Free Energy is equal to 0 or less
How is entropy change calculated?
Entropy change is the entropy of the products minus the entropy of the reactants
