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OCR A CHEM > ENTHALPY + ENTROPY > Flashcards

ENTHALPY + ENTROPY Flashcards

1
Q

what makes an ionic lattice very stable

A

strength of the ionic bond

- electrostatic attractions between oppositely charged ions in the structure

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2
Q

define lattice enthalpy

A

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

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3
Q

is lattice enthalpy exo or endo

A

it is ALWAY EXO –> making bonds

.:. value of enthalpy change is always neg

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4
Q

define enthalpy of formation

A

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

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5
Q

define enthalpy of atomisation

A

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

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6
Q

is enthalpy of atomisation endo or exo - why

A

endo –> bonds broken to form gas ions

.:. + value

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7
Q

define 1st ionisation energy

A

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

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8
Q

what is lattice enthalpy

A

measure of the strength of the ionic bond

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9
Q

define enthalpy of e- affinity

A

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

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10
Q

are ionisation energies endo or exo - why

A

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

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11
Q

what does e- affinity measure

A

the energy to gain e-

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12
Q

what does ionisation energy measure

A

the energy to lose e-

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13
Q

is electron affinity exo or endo - why

A

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

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14
Q

what type of energy change is this?

Ca (g) –> Ca+ (g) + e-

A

1st ionisation energy

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15
Q

what type of energy change is this?

S- (g) + e- –> S2- (g)

A

second e- affinity

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16
Q

what type of energy change is this?

Ca (s) + Cl2 (g) –> CaCl2 (s)

A

enthalpy of formation

17
Q

define enthalpy change of solution

A

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

18
Q

equation for energy change

A

q= mc∆T

19
Q

steps in the Born-Haber cycle

A
  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
20
Q

describe the dissolving process

A

ionic lattice breaks up

water molecules are attracted to and surround the ions

21
Q

steps in dissolving process

A
  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)
22
Q

factors affecting lattice enthalpy

A
  • Ionic size

- Ionic charge

23
Q

how does ionic size effect melting point

A

as ionic size incr, melting decr

  • ionic radius increases
  • attraction between ions decreases
  • lattice enthalpy less neg
  • melting point decreases
24
Q

how does ionic charge effect melting point

A

as ionic size incr, melting incr

  • ionic charge increases
  • attraction between ions increases
  • lattice enthalpy more neg
  • melting point increases
25
Q

Factors affecting hydration

A

ionic size

ionic charge

26
Q

how does ionic size effect hydration

A
  • ionic radius increases
  • attraction between ions and H2O decreases
  • hydration energy less neg
27
Q

what is entropy

A

the measure of disorer

28
Q

relationship between entropy and changing state

A

solid –> liquid –> gas

increasing entropy

29
Q

relationship between entropy and moles

A

if products have more moles, increase in entropy

30
Q

how do you calculate entropy change

A

∆S = ∆S (prod) - ∆S (reactant)

31
Q

what must the value be for reaction to be feasible

A

o or neg

32
Q

whats the gibbs equation

A

∆G= ∆H-T∆S

33
Q

how to calculate what temp the reaction will be feasible at

A

T= ∆H/∆S

34
Q

limitations of free energy

A

sometimes reactions with neg ∆G dont take place

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

OCR A CHEM (9 decks)

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