17 thermodynamics Flashcards
define standard enthalpy of formation
enthalpy change when one mole of a compound is formed from its elements
in standard states
under standard conditions
define standard enthalpy of atomisation
enthalpy change when one mole of gaseous atoms are formed from elements in standard state
under standard conditions
define first electron affinity
enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions
each with a single negative charge
define first ionisation energy
enthalpy change when one mole of gaseous atoms is converted to a mole of gaseous ions
each with a single positive charge
define lattice formation enthalpy
enthalpy change when one mole of solid ionic compounds is formed from its gaseous ions
what is mean bond enthalpy?
the enthalpy change when one mole of gaseous molecules
each break a covalent bond to form 2 free radicals
averaged over a range of compounds
what is the standard enthalpy of hydration?
the standard enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions
what is the standard enthalpy of solution?
the standard enthalpy change when one mole of solute dissolved to form its aqueous ions
what is lattice dissociation enthalpy?
the standard enthalpy change when one mole of solid ionic compound dissociates into its gaseous ions
what are the two key factors that determine how exothermic a lattice enthalpy will be?
charge of ions
radius of ions
if an ion has more charge, what does this mean in terms of attraction?
more attraction to oppositely charged ion
if an ion is smaller, what does this mean in terms of attraction?
greater attraction to oppositely charged ion
what does CRAM stand for?
Charge
Radius
Attraction
More endo/exothermic
if a theoretical charge for an ionic compound is different to its actual charge, what does this mean?
the ionic compound has covalent character
what is covalent character?
“mimicking” covalent bond, wants to share electrons
what happens to the electron cloud in a compound with covalent character?
electron cloud becomes distorted
what is a point charge?
charge in only one space
what does the perfect ionic model say?
that ions are point charges and perfectly ionic
what does the Born Haber Cycle say about ionic compounds?
that ions are polarisable and have covalent character
if a compound has no covalent character, the lattice formation enthalpy calculated by the perfect ionic model is…
almost equal to the lattice formation enthalpy calculated by the Born Haber model
if an ionic compound has covalent character, it’s lattice formation enthalpy calculated by the perfect ionic model will be…
less exothermic than the lattice formation enthalpy calculated by the Born Haber model
how do you dissolve an ionic compound?
- break ionic bonds
- form bonds between water molecules and ions
what is entropy?
the amount of disorder
what is the unit of entropy?
JK-1 mol-1
does an increase in disorder increase or decrease entropy?
increase
does a decrease in moles decrease or increase disorder?
decrease
how can you calculate ΔS?
sum of S products - sum of S reactants
how do you calculate gibbs free energy?
ΔG = ΔH - T x ΔS
what is ΔG and what is its units?
gibbs free energy
kJ mol-1
what is ΔH and what is its units?
change in enthalpy
kJ mol-1
what is T and what is its units in the gibbs free energy equation?
temperature
K
what is ΔS and what is its units?
change in entropy
kJK-1 mol-1
when is a reaction feaible?
if ΔG is less than or equal to 0
how do you calculate the temperature at which a reaction becomes feasible?
T = ΔS/ΔH
