3.1.8 Thermodynamics Flashcards
The standard molar enthalpy of formation
When one mol of a compound is formed from its elements at standard states at standard conditions.
Elements → compound
The standard enthalpy of atomisation
The enthalpy change of one mol of gaseous atoms form the elements at standard states understandard conditions.
Atom → 1 mol of gaseous atom
First ionisation energy
The standard enthalpy changes when 1 mol of gaseous atoms is converted to one mol of gaseous ions each with a single positive charge.
Metal atom → 1+ion
Second ionisation energy
The loss of a mol of electrons from a mol of 1+ions
1+ion → 2+ion
First electron affinity
When a mol of gaseous atoms is converted to a mol of gaseous 1- ions
Non metal atom → 1-ion
Second electron affinity
When a mol of electrons is added to a mol of gaseous ions with a 1- charge
1-ion → 2-ion
Lattice enthalpy of formation
When one mol of solid ionic compound is formed from its gaseous ions
Gaseous ions → ionic compound
When a lattice is formed energy is released. Separating requires energy.
Trends in lattice enthalpy
Larger ion = smaller lattice enthalpy (as the opposite charges are further apart)
For ions of a similar radius it increases with the charge of the ion.
Theoretical compound
Can predict lattice enthalpy of formation theoretically using born haber cycles.
Can you predict from the size of the metal ion and the structure of the crystals ???
find the enthalpy change of hydration when an ionic solid is dissolved in water
Enthalpy change of Lattice of dissociation
Pos ions hydrated lattice enthalpy of hydration given out
Neg ions hydrated lattice enthalpy of hydration given out
Lattice enthalpy of dissociation
The ionic lattice breaks to give separate gaseous ions.
ionic lattice → separate gaseous ions
Difference between theoretical lattice enthalpy predictions
Polarisation when small highly charged negative ions disrupt large highly charged negative ions. Leading to a degree of covalent bonding. Causing a difference between theoretical values.
Forces that make chemical reactions happen
Increase in entropy - increase in randomness delta S
Decrease in enthalpy - decrease in energy delta H
What are feasible reactions favoured by
Positive entropy changes +delta s (products more random than reactants)
Negative enthalpy changes (energy given out)
Gibbs free energy equation
delta G = delta H - T delta S
T = temperature
Value of delatG where it is feasible
0
So can calculate the temperature at which the reaction becomes feasible
born habour cycle calculation
arrow going oposite to direction = arrows going the correct direction
delta H of solution
= delat H lattice dissociation - (delta H hydra cation + delat H of hydr of anion)
multiply the delta hydra by the nub of ion present for the anion or cation
entropy at diffrent states
gas is more disordered than a solid
when us teh standard entropy os a substance 0
at OK
as particals are stationary meaning no vibration
meaning no dissorder
difference between boiling and melting
boiling has a bigger change in dissorder thena melting
delta G =
AH -TAS
linear realtionship
why delta G decreases as T increases
as Tdelta S gets bigger as the particals are moving more meaning ore dissorder
frsible when …
delta G is negative
how to calculate delat S from a table
products - reactants
what happens at a standard state
entropy data is wrong
reason the first elctron affinity of oxygen in an exothermic process
attractive force between the nucleas of atom and external electron
dela solution of a compound =
A H lattce enthalpy of the compound
