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Alevel Chemistry OCR A > Module 5: Enthalpoy And Entropy > Flashcards

Module 5: Enthalpoy And Entropy Flashcards

1
Q

Definitions
What is enthalpy of formation

A

Enthalpy change when one mole of a substance is formed from its elements in their standard state

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2
Q

Definitions
What type of energy change is enthalpy of formation

A

Exothermic for most

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3
Q

Definitions
Equation for enthalpy of formation for sodium oxide

A

2Na(s) + 1/2 O2(g) —> Na2O(s)

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4
Q

Definitions
What is enthalpy of combustion

A

Enthalpy change when one mole of a substance undergoes complete combustion with all substances in their standard states

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5
Q

Definitions
What type of energy change is enthalpy of combustion

A

Exothermic

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6
Q

Definitions
What is the equation for combustion of ethane

A

C2H6 + 7/2 O2 —> 2 CO2 + 3 H2O

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7
Q

Definitions
What is enthalpy of neutralisation

A

Enthalpy change when one mole of water is formed in a reaction between an acid and alkali under standard conditions

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8
Q

Definitions
What energy change is enthalpy of neutralisation

A

Exothermic usually -57

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9
Q

Definitions
Equation for enthalpy of neutralisation for sulfuric acid and sodium hydroxide

A

1/2 H2SO4 (aq) + NaOH (aq) —> 1/2 H2SO4 (aq) + H2O (l)

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10
Q

Definitions
What is the first ionisation energy

A

Enthalpy Chang when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous 1- ions

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11
Q

Definitions
What type of reaction is first ionisation energy

A

Endothermic

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12
Q

Definitions
Equation for first ionisation energy of magnesium

A

Mg(g) —> Mg+ (g) + e-

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13
Q

Definitions
What is second ionisation energy

A

Enthalpy can change when one mole of gaseous 1+ ions loses one. Ole of electrons to form one mole of gaseous 2+ ions loses

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14
Q

Definitions
What energy change is second ionisationnnenegry

A

Endothermic

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15
Q

Definitions
Equation for second ionisation energy for magnesium

A

Mg+(g) —> Mg2+ (g) + e-

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16
Q

Definitions
What is the first electron affinity

A

Enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mol of 1- ions

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17
Q

Definitions
What type of energy change is first electron affinity

A

Exothermic for many non metals

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18
Q

Definitions
Equations for first electron affinity of oxygen

A

O(g) + e- —> O-(g)

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19
Q

Definitions
What is second electron affinity

A

Enthalpy Change when one mole of gaseosus 1– ions gains one mole of electrons to form one mole of gaseous 2- ions

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20
Q

Definitions
What type of energy change is second electron affinity and why

A

Endothermic as adding negative electrons to a negative ion so some repulsion

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21
Q

Definitions
Equation for second electron affinity of oxygen

A

O- (g) + e- —> O2- (g)

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22
Q

Definitions
What is enthalpy of atomisation

A

Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state

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23
Q

Definitions
What type of energy change is enthalpy of atomisation

A

Endothermic

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24
Q

Definitions
Equation for enthalpy of atomisation of iodine

A

1/2 I2 (s) —> I (g)

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25
Q

Definitions
What is hydration enthalpy

A

Enthalpy change when one mole of gaseous ions dissolve in sufficient water to five an infinitely dilute solution

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26
Q

Definitions
What type of energy b change is hydration enthalpy

A

Exothermic

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27
Q

Definitions
Equation for hydration enthalpy of magnesium

A

Mg2+ (g) —> Mg2+ (aq)

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28
Q

Definitions
What is enthalpy of solution

A

Enthalpy change when one mole of ionic substance dissolves in water to give an infinitely dilute solution

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29
Q

Definitions
What type of energy change is enthalpy of solution

A

Varies

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30
Q

Definitions
Equation for enthalpy og solution of magnesium chloride

A

MgCl2 (s) —> Mg2+ (aq) + 2 Cl- (aq)

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31
Q

Definitions
What is bond dissociation enthalpy

A

Enthalpy changes when one mole of covalent bonds is broken in the gaseous state

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32
Q

Definitions
What energy change is bond dissociation enthalpy

A

Endothermic

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33
Q

Definitions
Equation for Bond dissociation enthalpy of I2

A

I2 (g) —> 2 I(g)

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34
Q

Definitions
What is lattice enthalpy of formation

A

Enthalpy change when one mole of solid ionic lattic is formed from gaseous ions

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35
Q

Definitions
When energy change is lattic enthalpy of formation

A

Exothermic

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36
Q

Definitions
Equation for lattic enthalpy of formation for magnesium chloride

A

Mg2+ (g) + 2 Cl-(g) —> MgCl2 (s)

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37
Q

Definitions
What is enthalpy of vaporisation

A

Enahtlpy change when one mole of a liquid is turned into a gas

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38
Q

Definitions
What energy change is enthalpy og vaporisation

A

Endothermic

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39
Q

Definitions
Equation for enthalpy of vaporisation of water

A

H2O (l) —> H2O(g)

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40
Q

Definitions
What is enthalpy of fusion

A

Enthalpy change when one mole of a solid is tuned into a liquid

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41
Q

Definitions
What energy change is enthalpy of fusion

A

Endothermic

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42
Q

Definitions
Equation for enthalpy of fusion for magnesium

A

Mg (s) —> Mg(l)

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43
Q

Lattice enthalpy
What is lattic enthalpy

A

Enthalpy change when one mole on a solid ionic compound is formed from its gaseous ions under standard conditions

44
Q

Lattice enthalpy
Equation for lattice enthalpy of potassium chloride

A

K+(g) + Cl-(g) —> KCl (s)

45
Q

Lattice enthalpy
What kind of energy change and why

A

Exothermic as involves formation of ionic bond

46
Q

Lattice enthalpy
What is lattic enthalpy also a measure of

A

Ionic bond strength

47
Q

Lattice enthalpy
What does a more negative lattic enthalpy value suggest

A

Stronger ionic bonding

48
Q

Lattice enthalpy
What is lattic enthalpy dependent upon

A

Charge density

49
Q

Lattice enthalpy
What two things is charge density dependent on

A

Ionic charge
Size of ion

50
Q

Lattice enthalpy
What does a higher charge on the ion mean for lattic enthalpy

A

More energy is released when lattic formed due to stronger electrostatic forces between ions so more negative lattice enthalpy

51
Q

Lattice enthalpy
What does a smaller atomic radii of ions mean for lattic enthalpy;py

A

More exothermic as have higher charge density and ions can sit closer together in lattice

52
Q

Lattice enthalpy
Will LiCl or KCl have more negative lattice enthalpy

A

LiCl has more negative lattice enthalpy as higher charge density due to smaller ion

53
Q

Lattice enthalpy
Will MgCl2 or NaCl have a more negative lattic enthalpy and why

A

MgCl2 as higher charge so greater lattice strength due to greater charge density

54
Q

Lattice enthalpy
How can lattic enthalpy of a compound be found

A

Using a born haber cycle

55
Q

Lattice enthalpy
What is lattice enthalpy bvalue determined by born haber cycles named as and why

A

Experimental value as data used in cycle is determined by experiments

56
Q

Born haber cycles for lattice enthalpy
What is a born haber cycle

A

Cycles that includes all the enthalpy changes in the formation of the ionic compound

57
Q

Born haber cycles for lattice enthalpy
What is the lattic enthalpy shown as for this

A

Negative so equation can be written

58
Q

Born haber cycles for lattice enthalpy
What equation can be made from born haber

A

Enthalpy of formation of the ionic compound equals sum of all other enthalpy changes

59
Q

Born haber cycles for lattice enthalpy
What has to be drawn for each enthalpy change

A

A separate step

60
Q

Born haber cycles for lattice enthalpy
What does Hess law say

A

Total enthalpy change of reaction is always the same independent of whoich route taken

61
Q

Born haber cycles for lattice enthalpy
What is the route 1

A

Enthalpy of formation
From elements in standard states down (exo) to solid ionic compound

62
Q

Born haber cycles for lattice enthalpy
What is route 2

A

From elements in standard state, atomisation of metal, atomisation of nonmetal, ionisation of metal, electron affinity of non metal, lattic enthalpy of formtionn

63
Q

Born haber cycles for lattice enthalpy
Describe arrow for atomisation enthalpy of metals

A

Arrow going from elements in standard states up (endo) to gaseous atom of metal and standard state non metal

64
Q

Born haber cycles for lattice enthalpy
Describe arrow for atomisation of non metal

A

From gaseous metal atom and standard state non metal going up (endo) to gaseous metal atom and gaseous non metal atom

65
Q

Born haber cycles for lattice enthalpy
Describe ionisation of metal

A

All ionisation energy endo so going up
From gases of metal atom and ghaeosu non metal atom to gaseous metal ion and gaseous non metal atom and electron
Do each ionisation energy in individual step n

66
Q

Born haber cycles for lattice enthalpy
Describe first electron affinity of non metal

A

Goes down as exothermic
From gaseous metal ion and gaseaous non metal atom and electrons to gaseous metal ion and gaseous non metal 1- ion (and electron)

67
Q

Born haber cycles for lattice enthalpy
What is different about second electron affinity of non metal

A

Endothermic so arrow going upwards

68
Q

Born haber cycles for lattice enthalpy
Describes arrow for lattic enthalpy of the ionic product

A

Goes from gaseous ions of solid ionic product
Arrow goes down as exothermic

69
Q

Born haber cycles for lattice enthalpy
What do need to be careful of when doing born haber

A

If need multiple species may have multiples of each enthalpy change

70
Q

Solution and hydration
What is enthalpy of solution

A

Enthalpy change when one mol of ionic substance dissolves in water to give a solution of infinite dilution

71
Q

Solution and hydration
Equation for enthalpy of solution for sodium chloride

A

NaCl(s) —> Na+ (aq) + Cl- (aq)

72
Q

Solution and hydration
What is the energy h age for enthalpy of solution

A

Can be either

73
Q

Solution and hydration
What is enthalpy of hydration

A

Enthalpy change when one mol of gaseous ions dissolves in sufficient water to give a infinitely dilute solution

74
Q

Solution and hydration
Equation for enthalpy of hydration for chlorine

A

Cl-(g) —> Cl-(aq)

75
Q

Solution and hydration
What is the energy change for enthalpy of hydration

A

Expothermic

76
Q

Solution and hydration
What can be constructed for these

A

Born haber cycles

77
Q

Solution and hydration
What goes at the top of these born haber cycles

A

Gaseous ions

78
Q

Solution and hydration
What always goies down from gaseous ions

A

Lattice enthalpy ands the hydration enthalpies of both species

79
Q

Solution and hydration
What can change about these cycles

A

Whether enthalpy of solution is endo or exo so can change position

80
Q

Entropy
What letter is given to entropy

81
Q

Entropy
What is it a measure of

82
Q

Entropy
What is the term entropy used for

A

The dispersal of energy within the chemicals making up the chemical system

83
Q

Entropy
What does the greater the entropy ,mean

A

More disorder

84
Q

Entropy
What is the units

A

J K^-1 mol^-1

85
Q

Entropy
What state has the greatest entropy

86
Q

Entropy
What state has the lowest entropy

87
Q

Entropy
What two factors can affect change in entropy

A

Number of moles
State

88
Q

Entropy
How do you explain increase in entropy due to change in state

A

Increase in entropy as particles are becoming more disordered

89
Q

Entropy
What happens to entropy as temperature increases

A

Entropy increases as faster particles move or vibrate so entropy increases

90
Q

Entropy
How can you predict the change in entropy from number of moles

A

If more moles on product side increase in entropy as have more moles of particles with disorder

91
Q

Entropy
What are standard entropy’s

A

Entropy of one mole of a substance under standard conditions

92
Q

Entropy
How do you calculate delta S

A

Sum of Sproducts - sum of Sreactants

93
Q

Free energy
What is feasibility

A

Term describes whether a reaction is able to happen and energetically feasible

94
Q

Free energy
What word may be used instead of feasibliklity

A

Spontaneous

95
Q

Free energy
What is the equation

A

/\G = /\H - T /\S

96
Q

Free energy
What is /\G and units

A

Gibbs free energy (overall change in energy during reaction)
kJ mol^-1

97
Q

Free energy
What is /\ H and units

A

Enthalpy change with surroundings in kJ mol^-1

98
Q

Free energy
What is T sand units

A

Temperature in kelvin

99
Q

Free energy
What is /\S and units

A

Change in entropy in J K^-1 mol^-1

100
Q

Free energy ***
What is key in doing this equation

A

Convert /\S from J to kJ but divide by 1000

101
Q

Free energy
What has to be true for a reaction to be feasible

102
Q

Free energy
What is a reaction being feasible dependent on

A

Temperature

103
Q

Free energy
How do you work out point at which reaction switches from being feasible to not

A

/\G=0 in equation using same /\H and /\S

104
Q

Free energy
Why may a reaction not be feasible

A

If has a very high Ea

105
Q

Free energy
H0w can this equation be applied to a graph

A

/\G on y axis
T on x axis
-/\S is gradient
/\H is the y intercept

Alevel Chemistry OCR A (16 decks)

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