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Chemistry A Level > Chapter 17 - Thermodynamics Year 2 > Flashcards

Chapter 17 - Thermodynamics Year 2 Flashcards

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1
Q

Definition of STANDARD ENTHALPY OF FORMATION, ΔHf⍬

A

The enthalpy change when one mole of a compound is formed from its elements with all reactants and products in their standard states.
ΔH = positive OR negative

eg. Mg (s) + Cl2 (g) → MgCl2 (s)

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2
Q

What is the definition of STANDARD ENTHALPY OF COMBUSTION, ΔHc⍬

A

The enthalpy change when one mole of an element or compound is completely burned in oxygen, with all reactants and products in their standard states.
ΔH = negative

eg. C (s) + O2 (g) → CO2 (g)

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3
Q

What is the definition of STANDARD ENTHALPY OF ATOMISATION (Element), ΔHat⍬

A

The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
ΔH = positive

eg. ½ Cl2 (g) → 2 Cl (g)

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4
Q

What is the definition of STANDARD ENTHALPY OF ATOMISATION (Compound), ΔHat⍬

A

The enthalpy change when one mole of a compound in its standard state is converted into gaseous atoms.
ΔH = positive

eg. CH4 (g) → C(g) + 4H(g)

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5
Q

What is the definition of BOND DISSOCIATION ENTHALPY, ΔHdis⍬

A

The enthalpy change when one mole of gaseous molecules each breaks a particular covelant bond to form two radicals.
ΔH = positive

eg. CH4 (g) → CH3 (g) + H(g)
eg. Cl2 (g) → 2Cl (g)

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6
Q

What is the definition of IONISATION ENTHALPY, ΔHIE⍬
1st Ionisation Enthalpy

A

The enthalpy change when one mole of gaseous atoms is converted into one mole of gaseous, singly charged, positive ions.
ΔH = positive

eg. Na (g) → Na+ (g) + e-

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7
Q

What is the definition of IONISATION ENTHALPY, ΔHIE⍬
2nd Ionisation Enthalpy

A

The enthalpy change when one mole of gaseous, singly charged, positive ions is converted into one mole of gaseous, doubly charged positive ions.
ΔH = positive

eg. Mg+(g) → Mg2+ (g) + e-

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8
Q

What is the definition of ELECTRON AFFINITY, ΔHEA⍬
1st Electron Affinity

A

The enthalpy change when one mole of gaseous atoms is converted into one mole of gaseous, singly charged, negative ions
ΔH = negative

eg. O (g) + e- → O- (g)

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9
Q

What is the definition of ELECTRON AFFINITY, ΔHEA⍬
2nd Electron Affinity

A

The enthalpy change when one mole of gaseous, singly charged, negative ions is converted into one mole of gaseous, doubly charged negative ions.
ΔH = positive

eg. O- (g) + e- → O2- (g)

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10
Q

What is the definition of LATTICE ENTHALPY, ΔHlatt⍬
Lattice Dissociation Enthalpy

A

The enthalpy change when one mole of an ionic compound is separated into its gaseous ions.
ΔH = positive

eg. MgCl2 (s) → Mg2+ (g) + 2 Cl- (g)

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11
Q

What is the definition of LATTICE ENTHALPY, ΔHlatt⍬
Lattice Formation Enthalpy

A

The enthalpy change when one mole of an ionic compound is formed from its gaseous ions.
ΔH = negative

eg. Mg2+ (g) + 2 Cl- (g) → MgCl2 (s)

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12
Q

What is the definition of ENTHALPY OF HYDRATION, ΔHhyd⍬

A

The enthalpy change when one mole of gaseous ions is converted into one mole of aqueous ions.
ΔH = negative

eg. Na+ (g) + aq → Na+ (aq)

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13
Q

What is the definition of ENTHALPY OF SOLUTION, ΔHsol⍬

A

The enthalpy change when one mole of an ionic compound dissolves in water to give a solution of infinite dilution.
ΔH = positive OR negative

eg. NaCl (s) + aq → Na+ (aq) + Cl- (aq)

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14
Q

What is HESS’S LAW

A

The enthalpy change for a reaction depends only on the initial and final states of the reaction and is independent of the route by which the reaction may occur.

e.g. ΔH1 = ΔH2 + ΔH3 + ΔH4

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15
Q

What is the Born-Haber cycle

A

It is an energy cycle that includes the enthalpy of lattice formation of an ionic compound and shows every step within that cycle

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16
Q

What reactions are in a Born-Haber Cycle

A

Enthalpy of formation
Enthalpy of atomisation of element 1
Enthalpy of atomisation of element 2
1st ionisation energy
(2nd and 3rd ionisation energy)
Electron affinity
Lattice formation enthalpy

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17
Q

What do lattice enthalpies tell us

A

The strength of ionic bonding
Higher lattice enthalpy = stronger ionic bonding

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18
Q

What can ionic and covalent bonding be imagined

A

they are 2 extremes at either end of a continuum with some molecules have characters of both ionic and covalent

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19
Q

What causes covalent character in a ionic bond

A

It is caused by polarisation

20
Q

How does polarisation work

A

When a small positive ion is near a large negative ion it distorts the shape of the electron cloud in the negative ion
This pulls electrons towards the positive ion causing to many electrons between the ions giving covalent characters

21
Q

when is polarisation most likely to occur

A

small highly positive ions next to large highly negative ions

22
Q

What are experimental lattice enthalpies

A

They are values using real data from experiments

23
Q

What are theoretical lattice enthalpies

A

Where the values assume bonding is purely ionic and the ions are perfectly spherical

24
Q

What is the difference between theoretical and experimental enthalpies

A

They show us how purely ionic bonding is in a reaction

25
Q

What is the theoretical model of dissolving

A

Solid to gas is lattice dissociation enthalpy
Gas to hydrated ions is enthalpy of hydration
Equal to enthalpy of solution

26
Q

What means a compound is soluble

A

enthalpy of solution is less than +30
The more negative, the more soluble

27
Q

What is the equation for enthalpy of solution

A

lattice enthalpy + enthalpy of hydration

28
Q

How is enthalpy of hydration measured

A

It isn’t possible to measure the enthalpy of hydration of a single ion so the value is the sum of 2 enthalpies of hydration

29
Q

what factors affect enthalpy of hydration

A

Charge of ions
size of ions

30
Q

How does charge of ions affect the enthalpy of hydration

A

higher charge is greater attraction and trhe more negative enthalpy

31
Q

How does ion size affect enthalpy of hydration

A

The bigger it is, the smaller the attraction so bigger enthalpy

32
Q

What is a spontaneous change

A

It is one which just happens without any extra energy needing to be supplied to it at a particular temperature

33
Q

What is entropy

A

It is a measure of the degree of disorder in a system

34
Q

What ways are entropy increased

A

melting
evaporation
solution from solid
gas from solids or liquids
when the number of molecules increases

35
Q

What are the units of entropy change

A

J/K/mol

36
Q

What is the equation for entropy change of reaction

A

entropy of products - entropy of reactants

37
Q

What is the equation for total entropy change

A

entropy of reaction + entropy of surrondings

38
Q

What is the equation of entropy of surrondings

A

-enthalpy change / temperature

39
Q

What influences spontaneous reactions

A

enthalpy and entropy change

40
Q

What is the equation for Gibbs free energy chnage

A

enthalpy change - temperature x Entropy change

41
Q

What means a reaction is feasible

A

negative gibbs free energy change

42
Q

What does gibbs free energy change equal for an equilibrium process

A

0

43
Q

What is an equilibrium change

A

change of state

44
Q

When is the standard entropy of an element 0

A

0 K

45
Q

What is an enthalpy change

A

Heat (energy) change at constant pressure

Chemistry A Level (20 decks)

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