module 5.2 - physical chemistry and transition elements: energy Flashcards
lattice enthalpy definition
enthalpy change when 1 mol of an ionic compound is formed from its gaseous ions under standard conditions
what is lattice enthalpy a measure of
energy released when forming an ionic bond in a giant ionic lattice
enthalpy change of atomisation
enthalpy change when 1 mol of gaseous atoms is formed from the elements in its standard state under standard conditions
electron affinity
enthalpy change when 1 electron is added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous negative ions under standard conditions
enthalpy change of formation
enthalpy change when 1 mol of a compound is formed from its elements under standard conditions
first ionisation energy definition
the energy required to remove 1 mol of electrons from 1 mol of atoms of an element in the gaseous state to form 1 mol of gaseous ions.
why can’t we use Hess’ Law to measure lattice enthalpy
cause we can’t measure lattice enthalpy directly so we do it indirectly
what do we use to measure lattice enthalpy
Born Haber cycle
enthalpy change of solution
enthalpy change when 1 mol of a solute dissolves into a solvent under standard conditions
enthalpy change of hydration
enthalpy change when 1 mol of gaseous ions are hydrated to form 1 mol of aqueous ions
entropy definition
measure of the dispersal of energy in a system
greater entropy =
greater dispersal of energy = greater disorder
difference in entropy between states of matter
gas > liquid > solid
calculation for entropy change in a system
∆S⦵ = ∑S⦵ (products) - ∑S⦵ (reactants)
what must happen in a reaction for it to be deemed feasible
- must occur spontaneously
what must decrease in order for a reaction to be feasible
gibb’s free energy
equation to calculate free energy change
∆G = ∆H - T∆S
unit of measure for ∆G
KJ mol-1
unit of measure for ∆H
KJ mol-1
unit of measure for T
kelvin (+273)
unit of measure for ∆S
Jmol-1K-1 (divide by 1000)
what must the value of ∆G be for the reaction to be feasible
∆G has to be a negative value (∆G < 0)
limitations of using ∆G
- just because the reaction is feasible doesn’t mean it will occur at an observable rate
- while ∆G can be used to determine the feasibility of a reaction, it does not take into account the kinetics of the reaction i.e rate of reaction
- some reactions are feasible but very slow
finding minimum temp
rearrange Gibbs equation with ∆G as 0 to find T
T= ∆H/∆S
