ENTHALPY + ENTROPY

Question 1

what makes an ionic lattice very stable

Answer 1

strength of the ionic bond

- electrostatic attractions between oppositely charged ions in the structure

Question 2

define lattice enthalpy

Answer 2

the energy change that takes place when one mole of an ionic compound is formed from it constituent gaseous ions, under standard conditions

Question 3

is lattice enthalpy exo or endo

Answer 3

it is ALWAY EXO –> making bonds

.:. value of enthalpy change is always neg

Question 4

define enthalpy of formation

Answer 4

the energy change that takes place when 1 mole of a compound is formed from its constituent elements under standard conditions

Question 5

define enthalpy of atomisation

Answer 5

the energy change that takes place when 1 mole of gaseous atoms are formed from the element in its standard state

Question 6

is enthalpy of atomisation endo or exo - why

Answer 6

endo –> bonds broken to form gas ions

.:. + value

Question 7

define 1st ionisation energy

Answer 7

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

Question 8

what is lattice enthalpy

Answer 8

measure of the strength of the ionic bond

Question 9

define enthalpy of e- affinity

Answer 9

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

Question 10

are ionisation energies endo or exo - why

Answer 10

endo - bc energy is required to overcome the attraction between a neg e- and pos nucleus

Question 11

what does e- affinity measure

Answer 11

the energy to gain e-

Question 12

what does ionisation energy measure

Answer 12

the energy to lose e-

Question 13

is electron affinity exo or endo - why

Answer 13

exo - the e- being added is attracted towards the nucleus

Question 14

what type of energy change is this?

Ca (g) –> Ca+ (g) + e-

Answer 14

1st ionisation energy

Question 15

what type of energy change is this?

S- (g) + e- –> S2- (g)

Answer 15

second e- affinity

Question 16

what type of energy change is this?

Ca (s) + Cl2 (g) –> CaCl2 (s)

Answer 16

enthalpy of formation

Question 17

define enthalpy change of solution

Answer 17

the energy change when 1 mol of a solute dissolved in a solvent

Question 18

equation for energy change

Answer 18

q= mc∆T

Question 19

steps in the Born-Haber cycle

Answer 19

1. FORMATION OF GAS ATOMS
   - ->elements in standard states –> gas atoms
   - -> this is EXO bc bond breaking
2. FORMATION OF GAS IONS
   - -> gaseous atoms –> + & - gas ions
   - -> overall endo
3. LATTICE FORMATION
   - -> gaseous ions –> solid ionic lattice

Question 20

describe the dissolving process

Answer 20

ionic lattice breaks up

water molecules are attracted to and surround the ions

Question 21

steps in dissolving process

Answer 21

1. ionic lattice breaks to form separate gaseous ions (LATTICE ENTHALPY)
2. the separate ionic gas ions interact w/ polar water molecule to form aqueous ions
   (HYDRATION)

Question 22

factors affecting lattice enthalpy

Answer 22

• Ionic size

- Ionic charge

Question 23

how does ionic size effect melting point

Answer 23

as ionic size incr, melting decr

• ionic radius increases
• attraction between ions decreases
• lattice enthalpy less neg
• melting point decreases

Question 24

how does ionic charge effect melting point

Answer 24

as ionic size incr, melting incr

• ionic charge increases
• attraction between ions increases
• lattice enthalpy more neg
• melting point increases

Question 25

Factors affecting hydration

Answer 25

ionic size

ionic charge

Question 26

how does ionic size effect hydration

Answer 26

• ionic radius increases
• attraction between ions and H2O decreases
• hydration energy less neg

Question 27

what is entropy

Answer 27

the measure of disorer

Question 28

relationship between entropy and changing state

Answer 28

solid –> liquid –> gas

increasing entropy

Question 29

relationship between entropy and moles

Answer 29

if products have more moles, increase in entropy

Question 30

how do you calculate entropy change

Answer 30

∆S = ∆S (prod) - ∆S (reactant)

Question 31

what must the value be for reaction to be feasible

Answer 31

o or neg

Question 32

whats the gibbs equation

Answer 32

∆G= ∆H-T∆S

Question 33

how to calculate what temp the reaction will be feasible at

Answer 33

T= ∆H/∆S

Question 34

limitations of free energy

Answer 34

sometimes reactions with neg ∆G dont take place

–> this is because it may have a large activation energy + slow rate