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chemistry > topic 13 > Flashcards

topic 13 Flashcards

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1
Q

what is the enthalpy chnage of 1st electron afinity

A

the enthalpy change when 1 mole of gaseous 1- ions are made from 1 mole of gaseous atoms
O(g) –> O- (g)

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2
Q

what is the lattice enthalpy of formation

A

the enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions under standard condition
Ca 2+ (g) + 2Cl- (g) –> CaCl2 (s)

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3
Q

what is the enthalpy change of second electron affinity

A

the enthalpy change when 1 mole of gaseous 2- ions are made form 1 mole of gaseous 1- ions
O- (g) –> O 2- (g)

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4
Q

what is the enthalpy change of atomisation

A

the enthalpy change when 1 mole of gaseous atoms is made from an element in its standard state
!/2 F2 (g) —> F (g)

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5
Q

what affects the strenght of an ionic bond

A

size of the charge
- bigger chrges = stronger electrostatic attraction
- more energy required so increased mp

size of ion
- smaller ion = stronger electrostatic attraction
- smaller ions can pack closer and more energy required to overcome so increased mp

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6
Q

draw a born haber cycle for lithium chloride

A

see flash card

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7
Q

draw a born haber cycle for magnesium oxide

A

see flash card

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8
Q

what is theoretical lattice enthalpies

A

calculated from data assuming a perfectly ionic
- ions are perfectly spherical
- charge is evenly distributed

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9
Q

what is experimental lattice enthalpies

A

can be different to theoretical as ionic comound has covalent chaacterisitcs, more polarisation = more covalent
positive ion polarised negative ion

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10
Q

what causes higher polarisation

A

smaller cations more polarising = higher charge density so pulls electrons towards itself more readily
large anions with large charge are polarised more easily = electrons further away from nucleus and more repulsion between electrons in ion

small ions
larger charge

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11
Q

what does more polarisation do to covalent character of and ionic compound

A

increases covalent character

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12
Q

what is electronegativity

A

the ability for an atom to attract electrons towards itself in a covalent bond

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13
Q

where are the most elctronegative elements in the periodic table

A

further up and right

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14
Q

what is electronegativity measured in

A

pauling scale

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15
Q

what does a big difference in electronegativity suggest

A

more ionic the substance

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16
Q

what is enthalpy change of solution

A

the enthalpy change when 1 mole of ionic substance is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution

17
Q

what is hydration

A

when the ionic lattice in solid form is mixed with water
substance bonds broken to create free moving ions
bonds formed between ions and water

18
Q

what must happen for a substance to dissolve

A

the new bonds formed must be same strength or greater than those broken
tend to have exothermic enthalpies of solution

19
Q

how to calculate enthalpy of solution

A

know lattice enthalpy of dissociation and hydration
see flash card for cycle

20
Q

what 2 things affect enthalpy of hydration and why

A

charge
- high charge attract water molecules more strongly as electrostatic attraction stronger, more energy released when bond is made so more exothermic enthalpy of hydration
- larger charge more -ve ethalpy of hydration

size
- smaller ions have higher charge density so can attract water molecules more strongly so more exothermic enthalpy of hyration
- smaller ion more -ve enthalpy of hydration

21
Q

what is entropy

A

measure of disorder in a system

22
Q

what does more disorder in a system mean in terms of enropy

A

higher entropy

23
Q

which out of solid liquid and gas has highest entropy

A

gas

24
Q

does more or less moles have higher entropy

A

more moles

25
Q

how can a enthalpically unfavourable (endothermic) still be feasible

A

if changes in enropy overcome changes in enthalpy

26
Q

how to work out entopy of system and what are the units

A

S products - S reactants
units = JK^-1mol^-1

27
Q

what is standard entropy

A

1 mole
100KPa
298K

28
Q

for a feasible reaction what must the entropy be

A

positive

29
Q

how to work out total entropy

A

entropy system + entropy surroundings

system = products - reactants

surroundingds = -AH in JKmol^1 / T in K

30
Q

what does gibbs free energy tell us

A

if a reaction is feasible or not

31
Q

how to work out gibbs free energy

A

AH - T AS system

AG - Jmol^-1
AH - Jmol_1
T - K
AS system - JK^-1mol^-1

32
Q

what must gibbs free energy be for reaction to be feasible

A

negative or 0

33
Q

how to calculate the temperature of feasibility

A

T + AH / AS system

T - K
AH - convert from KJ mol^-1 to Jmol^-1

34
Q

in terms of equilibrium constants what happens when gibbs is negative

A

reaction is theoretically feasible
equilibrium constants are large
greater than 1

35
Q

in terms of equilibrium constants what happens when gibbs is positive

A

reaction is not theoretically feasible
equilibrium constants are small
less than 1

36
Q

how to work out equilibrium constants using gibbs free energy

A

lnk = AG / - RT
k = e ^- ln

chemistry (15 decks)

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