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physical chem and transition elements Flashcards

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1
Q

what does enthalpy of formation mean?

A

the enthalpy change when 1 mole of a compound is formed from its element under standard conditions

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2
Q

what does ionisation enthalpy mean?

A

the amount of energy required to remove an electron from a gaseous atom of an element to from a gaseous ion under standard conditions

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3
Q

what does enthalpy change of atomisation mean?

A

the enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions

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4
Q

what does bond enthalpy mean?

A

the amount of energy required to break 1 mole of a specific covalent bond in the gas phase

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5
Q

what does lattice energy mean?

A

the enthalpy change when 1 mole of ionic compound is formed from its gaseous ions under standard conditions

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6
Q

what factors affect lattice enthalpy?

A

ionic radius
as it increases, attraction between ions decreases so lattice enthalpy becomes less exothermic and melting point decreases

ionic charge
as it increases, attraction between ions increases so lattice enthalpy becomes more exothermic and melting point increases

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7
Q

what does enthalpy change of solution mean?

A

the enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions

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8
Q

what does standard enthalpy change of hydration mean?

A

when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions

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9
Q

what does the entropy (S) of a given system mean?

A

the number of possible arrangements of the particles and energy in a given system

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10
Q

list the states in ascending order of entropy

A

solid, liquid, gas

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11
Q

what is the equation for change in entropy (S)

A

Σ S products - Σ S reactants

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12
Q

what is the Gibbs equation used to calculate?

A

if a reaction is feasible or not

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13
Q

what is the Gibbs equation?

A

ΔGꝋ = ΔHreactionꝋ - TΔSsystemꝋ

ΔGꝋ = ΣΔGproductsꝋ - ΣΔGreactantsꝋ

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14
Q

what does a negative ΔGꝋ value mean?

A

the reaction is feasible

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15
Q

what does a positive ΔGꝋ value mean?

A

the reaction is not feasible

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16
Q

in an exothermic reaction, what is the feasibility if ΔSsystemꝋ is positive?

A

both terms neg
neg ΔGꝋ
feasible

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17
Q

in an exothermic reaction, what is the feasibility if ΔSsystemꝋ is negative?

A

first term neg, second pos
at high temps, TΔSsystemꝋ is large and pos so overcomes ΔH
at high temps pos ΔGꝋ
not feasible

18
Q

what is ΔH in an exothermic reaction?

A

negative

19
Q

what is ΔH in an endo reaction?

A

positive

20
Q

in an endothermic reaction, what is the feasibility if ΔSsystemꝋ is negative?

A

both terms pos
pos ΔGꝋ
not feasible regardless of temp

21
Q

in an endothermic reaction, what is the feasibility if ΔSsystemꝋ is positive?

A

first term pos, second neg
at low temps TΔSsystemꝋ is small and neg
so ΔGꝋ pos
not feasible

more feasible at high temps

22
Q

what are the limitations of using ΔG?

A

can only be used under standard conditions
doesn’t take into account rate of reaction
some reactions are feasible but not kinetically feasible cos too slow

23
Q

what is an oxidising agent?

A

oxidise another atom/ ion by causing it to lose electrons
gets reduced- gains electrons
so oxidation number decreases

24
Q

what is a reducing agent?

A

reduces another atom/ ion by causing it to gain electrons
gets oxidised- loses electrons
so oxidation number increases

25
Q

explain potassium manganate (VII) titrations

A

manganate(VII) is oxidising agent
reduced to Mn2+
iron is reducing agent
oxidised to Fe3+
reaction mixture must be acidified to excess dilute sulphuric acid added to Fe3+ before reaction

potassium permanganate starts purple
Mn2+ is pale pink but appears colourless cos of low conc
when all Fe2+ reacted with Mn7+, pale pink solution due to excess Mn7+

26
Q

why is dilute sulphuric acid suitable for potassium manganate (VII) titrations?

A

does not oxidise under the conditions
does not react with manganate (VII)

27
Q

why is HCl not suitable for potassium manganate (VII) titrations?

A

can be oxidised to Cl by manganate (VII)

28
Q

why is nitric acid not suitable for potassium manganate (VII) titrations?

A

oxidising agent
may oxidise substances

29
Q

why is ethanoic acid not suitable for potassium manganate (VII) titrations?

A

weak acid
insufficient concentration of H+ ions

30
Q

why is conc sulphuric acid not suitable for potassium manganate (VII) titrations?

A

may oxidise substances

31
Q

explain iodine thiosulfate titrations

A

light brown/ yellow of iodine turns paler when converted to colourless iodide ions
when solution is a straw colour, starch is added
turns blue/black until all iodine reacts, then colour disappears

32
Q

what can iodine thiosulfate titrations be used for determining?

A

amount of chlorate(I) in bleach
amount of Cu2+ in copper(II) compounds
copper content of alloys

33
Q

what can potassium manganate titrations be used for determining?

A

percentage purity of iron supplements
formula of a sample of hydrated ethanedioic acid

34
Q

what does the position of equilibrium and electrode potential depend on?

A

temp
pressure of gases
conc of reagents

35
Q

what conditions are used when comparing electrode potentials?

A

standard
ion conc of 1moldm-3
298K
100kPa

36
Q

what is used to take standard electrode potential measurements?

A

high resistance voltmeter

so no current flows
and max pd achieved

37
Q

what is a standard hydrogen electrode?

A

contains hydrogen gas in equilibrium with H+ ions of concentration 1moldm-3 at 100kPa and an inert platinum electrode
0.00V

38
Q

what is standard electrode potential?

A

potential difference produced when a standard half cell is connected to a standard hydrogen cell under standard conditions

39
Q

which half cell is more likely to get reduced?

A

the more positive one

40
Q

which half cell is less likely to get reduced?

A

the more negative one

41
Q

what are the different types of half cells that can be connected to standard hydrogen electrodes?

A

metal/ metal ion
non metal/ non metal ion
ion/ ion

42
Q

why is platinum wire used as an electrode?

A

inert

chem (4 decks)

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