ENTHALPY + ENTROPY Flashcards
what makes an ionic lattice very stable
strength of the ionic bond
- electrostatic attractions between oppositely charged ions in the structure
define lattice enthalpy
the energy change that takes place when one mole of an ionic compound is formed from it constituent gaseous ions, under standard conditions
is lattice enthalpy exo or endo
it is ALWAY EXO –> making bonds
.:. value of enthalpy change is always neg
define enthalpy of formation
the energy change that takes place when 1 mole of a compound is formed from its constituent elements under standard conditions
define enthalpy of atomisation
the energy change that takes place when 1 mole of gaseous atoms are formed from the element in its standard state
is enthalpy of atomisation endo or exo - why
endo –> bonds broken to form gas ions
.:. + value
define 1st ionisation energy
the energy change required to remove 1 e- from an atom in 1 mol of gaseous atoms to form 1 mol of unipositive gaseous ions
what is lattice enthalpy
measure of the strength of the ionic bond
define enthalpy of e- affinity
the enthalpy change that takes place, under standard conditions, when 1 e- is added to each atom in 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions
are ionisation energies endo or exo - why
endo - bc energy is required to overcome the attraction between a neg e- and pos nucleus
what does e- affinity measure
the energy to gain e-
what does ionisation energy measure
the energy to lose e-
is electron affinity exo or endo - why
exo - the e- being added is attracted towards the nucleus
what type of energy change is this?
Ca (g) –> Ca+ (g) + e-
1st ionisation energy
what type of energy change is this?
S- (g) + e- –> S2- (g)
second e- affinity
what type of energy change is this?
Ca (s) + Cl2 (g) –> CaCl2 (s)
enthalpy of formation
define enthalpy change of solution
the energy change when 1 mol of a solute dissolved in a solvent
equation for energy change
q= mc∆T
steps in the Born-Haber cycle
- FORMATION OF GAS ATOMS
- ->elements in standard states –> gas atoms
- -> this is EXO bc bond breaking - FORMATION OF GAS IONS
- -> gaseous atoms –> + & - gas ions
- -> overall endo - LATTICE FORMATION
- -> gaseous ions –> solid ionic lattice
describe the dissolving process
ionic lattice breaks up
water molecules are attracted to and surround the ions
steps in dissolving process
- ionic lattice breaks to form separate gaseous ions (LATTICE ENTHALPY)
- the separate ionic gas ions interact w/ polar water molecule to form aqueous ions
(HYDRATION)
factors affecting lattice enthalpy
- Ionic size
- Ionic charge
how does ionic size effect melting point
as ionic size incr, melting decr
- ionic radius increases
- attraction between ions decreases
- lattice enthalpy less neg
- melting point decreases
how does ionic charge effect melting point
as ionic size incr, melting incr
- ionic charge increases
- attraction between ions increases
- lattice enthalpy more neg
- melting point increases
Factors affecting hydration
ionic size
ionic charge
how does ionic size effect hydration
- ionic radius increases
- attraction between ions and H2O decreases
- hydration energy less neg
what is entropy
the measure of disorer
relationship between entropy and changing state
solid –> liquid –> gas
increasing entropy
relationship between entropy and moles
if products have more moles, increase in entropy
how do you calculate entropy change
∆S = ∆S (prod) - ∆S (reactant)
what must the value be for reaction to be feasible
o or neg
whats the gibbs equation
∆G= ∆H-T∆S
how to calculate what temp the reaction will be feasible at
T= ∆H/∆S
limitations of free energy
sometimes reactions with neg ∆G dont take place
–> this is because it may have a large activation energy + slow rate
