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Edexcel A Level Chemistry - 2021 MMS EXAMS > ✅13 - Energetics II > Flashcards

✅13 - Energetics II Flashcards

1
Q

What is standard lattice energy?

A

The energy change when one mole of ionic solid is formed from its gaseous ions under standard conditions.

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2
Q

What is the equation for standard lattice energy for NaCl?

A

Na+(g) + Cl-(g) —-> NaCl(s)

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3
Q

What are the factors affecting the magnitude of lattice enthalpy?

A

The charge on the ion
The amount of cation-anion interactions in the molecule
The distance between the centres of the cations and the anions

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4
Q

What is the standard enthlapy change of atomisation?

A

The enthlapy change when one mole of gaseous atoms is formed from an element in its standard state.

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5
Q

What is the equation for the atomisation of Na?

A

Na(s) —-> Na(g)

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6
Q

What is electron affinity?

A

The first energy change is the change when each atom in one mole of atoms in the gaseous state gains an electron to form a -1 ion

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7
Q

What is the equation for the first electron affinity of Chlorine?

A

Cl(g) + e- —-> Cl-

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8
Q

Which enthlapy change goes on the bottom of the Born Haber cycle?

A

The enthlapy change of formation

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9
Q

What is experimental lattice energy?

A

That calculated from a Born-Haber cycle

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10
Q

What is theoretical lattice energy?

A

The value found from X-ray crystallography

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11
Q

What are the assumptions made with theoretical lattice energy?

A

The ions are in contact with one another
The ions are perfectly spherical
The charge on each ion is evenly distributed around the centre so that each ion can be considered as point charges

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12
Q

What does an agreement between theoretical and experimental lattice energies indicate?

A

That the ionic model is good for the compound, so it has good ionic character.

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13
Q

What does a significant difference between values for experimental and theoretical lattice energies indicate?

A

That the compound has significant covalent character

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14
Q

When is an ion polarised?

A

When the electrons are pulled towards the cation and the distribution of electron density is distorted

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15
Q

What factors increase polarisation?

A

A high charge and small size of the cation

A high charge and large size of the anion

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16
Q

Which ions are polarised most easily?

A

Anions with a large charge and large size

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17
Q

What is the enthalpy change of solution?

A

The energy change when one mole of an ionic solid dissolves in water to form an infinitely dilute solution

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18
Q

Upon dilution, how do the ions move?

A

They move apart (endothermic) and become more hydrated (exothermic)

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19
Q

How is the value for enthalpy change of solution found?

A

The value cannot be found experimentally so is found by a process of extrapolation.

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20
Q

What is the point of infinite dilution?

A

The point where further dilution has no measurable effect on the enthalpy change of solution.

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21
Q

What is the enthalpy change of hydration?

A

The enthalpy change when one mole of an ion in a gaseous state is completely hydrated in water

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22
Q

In practice, when has complete hydration occurred?

A

When the solution formed is of infinite dilution

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23
Q

What is ion-dipole interaction?

A

The interaction as a result of the attraction between the delta - oxygen atom of the water molecule and the cation.

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24
Q

What are the factors affecting the magnitude of hydration enthalpy?

A

The charge on the ion

The ionic radius

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25
Q

How does ionic radius affect hydration enthalpy?

A

As the ions get larger,the attraction between them and the water molecule decreases and the enthalpy of hydration decreases

26
Q

How does charge affect hydration enthalpy?

A

The higher the charge, the more negative the value

27
Q

What makes the products of a reaction energetically stable?

A

If they have less energy then the reactants

28
Q

What is a spontaneous process?

A

One which takes place without continuous intervention from us.

29
Q

What is entropy?

A

A property of matter that is associated with the degree of disorder, or degree of randomness, of the particles

30
Q

What is the second law of thermodynamics?

A

In a spontaneous reaction, the total entropy increases.

31
Q

What is the total entropy change?

A

The entropy change of the system and the entropy change of the surroundings

32
Q

What is the system in a chemical reaction?

A

The species taking part in the reaction

33
Q

What must the total entropy change be for a reaction to be spontaneous?

A

Positive

34
Q

What is the equation for the entropy change of the system?

A

S(products) - S(reactants)

35
Q

What is the equation for entropy change of the surroundings?

A

-ΔH / T

36
Q

What will ΔSsurroundings be for an exothermic reaction?

A

Positive

37
Q

What would ΔSsurroundings be for an endothermic reaction?

A

Negative, so the entropy decreases

38
Q

Ice has a lower entropy than water so ΔS system is…

A

…negative

39
Q

If a process is exothermic, ΔS surroundings is…

A

…Positive

40
Q

How does an increase in the number of moles change the entropy?

A

Increasing moles increases the entropy

41
Q

What changes take place when ionic solids dissolve in water?

A

The lattice is broken down

The ions become hydrated

42
Q

Is the hydration of ions endothermic or exothermic?

A

Exothermic

43
Q

How is the solubility of an ionic salt determined?

A

By its entropy change

44
Q

If a salt is soluble, is entropy positive or negative?

A

Positive

45
Q

What is the expression for Gibbs energy?

A

∆G = ∆H - T x ∆S system

46
Q

Is ∆G positive or negative if the reaction is spontaneous?

A

Negative

47
Q

If ∆G = 0, the reaction is…

A

…in equilibrium

48
Q

When will ∆G be negative?

A

∆H < 0 and ∆S > 0
∆H < 0 and ∆H > T ∆S
∆H > 0 and ∆H < T ∆S

49
Q

When is ∆G positive?

A

∆H > 0 and ∆S < 0
∆H > 0 and ∆H > T ∆S
∆H < 0 and ∆H < T ∆S

50
Q

What is the equation for the relationship between K and ∆G?

A

∆G = -RTlnK

51
Q

How can K be calculated using ∆G?

A

K = e^(-∆G/RT)

52
Q

If ∆G is negative, K is…

A

… greater than 1, so the products are favoured

53
Q

If ∆G is positive, K is…

A

…less than 1, so the reactants are favoured

54
Q

If ∆G is positive, can all the reactants be converted into products?

A

No, it is impossible

55
Q

How can K be calculated from temperature?

A

lnK = -∆H/RT + ∆S system/R

56
Q

If the reaction is exothermic and temperature is increased, what happens to K?

A

It decreases, reaction shifts to the left

57
Q

If the reaction is endothermic and temperature increases, what happens to K?

A

It increases, equilibrium shifts to the right

58
Q

Why may a reaction not take place spontaneously even if ∆G is negative?

A

If the activation energy is very high and cannot be reached spontaneously, the reactants are kinetically stable

59
Q

What sign does ∆G have for a strong acid?

A

-

60
Q

What sign does ∆G have for a weak acid?

A

+

Edexcel A Level Chemistry - 2021 MMS EXAMS (19 decks)

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