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Chemistry > Chapter 22 - Lattice enthalpy > Flashcards

Chapter 22 - Lattice enthalpy Flashcards

1
Q

What is lattice enthalpy the measure of ?

A

It is a measure of the strength of ionic bonding in a giant ionic lattice

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2
Q

Define lattice enthalpy

A

It is the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

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3
Q

What type of energy change is lattice enthalpy ?

A
  • It is an exothermic change
  • The value will always be negative
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4
Q

Does lattice enthalpy involve bond making or bond breaking ?

A
  • Bond making
  • Ionic bond formation from separate gaseous ions
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5
Q

What is the Born-Haber cycle ?

A

It is a type of energy cycle that allows you to calculate lattice enthalpy indirectly

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6
Q

How many routes are there in the Born-Haber cycle ?

A

There are 2 routes in the Born-Haber cycle

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7
Q

What are the three different processes in route 1 ?

A
  • Formation of gaseous atoms
  • Formation of gaseous ions
  • Lattice formation
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8
Q

What does the formation of gaseous atoms involve ?

A
  • Changing the elements in their standard states into gaseous atoms
  • This change is endothermic as it involves bond breaking
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9
Q

What does the formation of gaseous ions involve ?

A
  • Changing the gaseous atoms into positive and negative gaseous ions
  • Overall this change is endothermic
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10
Q

What does the process of lattice formation involve ?

A
  • Changing the gaseous ions into the solid ionic lattice
  • This is the lattice enthalpy and is exothermic
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11
Q

What is route 2 ?

A
  • It converts the elements in their standard states directly to the ionic lattice
  • There is only one enthalpy change
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12
Q

What is the enthalpy change for route 2 ?

A
  • Enthalpy change of formation
  • This is an exothermic enthalpy change
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13
Q

What is the standard enthalpy change of formation ?

A
  • It is the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions
  • With all reactants and products in their standard states
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14
Q

What is the standard enthalpy change of atomisation ?

A

It is the enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions

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15
Q

What kind of process is the standard enthalpy change of atomisation ?

A
  • It is an endothermic process
  • This is because bonds are broken to form gaseous atoms
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16
Q

What is the first ionisation energy ?

A

It is the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

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17
Q

Is the first ionisation energy exothermic or endothermic ?

A

Endothermic because energy is required to overcome the attraction between a negative electron and the positive nucleus

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18
Q

What is electron affinity ?

A

It is the opposite of ionisation energy

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19
Q

What does electron affinity measure ?

A

It measures the energy needed to gain electrons

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20
Q

What is the first electron affinity ?

A

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

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21
Q

Is the first electron affinity exothermic or endothermic ?

A

It is exothermic because the electron being added is attracted towards the nucleus

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22
Q

How do you determine lattice enthalpies ?

A

Using the Born-Haber cycle

23
Q

When are successive electron affinities required ?

A

When an anion has a greater charge than 1-, such as O2-

24
Q

Are second electron affinities exothermic or endothermic ?

A

They are endothermic

25
Q

Why are second electron affinities endothermic ?

A
  • A second electron is being gained by a negative ion, which repels the electron away
26
Q

Define standard enthalpy change of solution

A

The enthalpy change that takes place when one mole of a solute dissolves in a solvent.

27
Q

What mass should be used in enthalpy calculations ?

A

The mass of everything in the solution

28
Q

What processes take place when a solid ionic compound dissolves in water?

A
  • Ionic lattice breaks up
  • Water molecules are attracted to and surround the ions
29
Q

What are the energy changes involved in these processes of a solid ionic compound dissolving in water?

A
  • Ionic lattice is broken up forming separate gaseous ions
  • Separate gaseous ions interact with polar water molecules to form hydrated aqueous ions
  • Called enthalpy change of hydration
30
Q

Define enthalpy change of hydration

A

The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.

31
Q

What can the values of the enthalpy change of solution be ?

A

Exothermic and endothermic

32
Q

What are the general properties of ionic compounds ?

A
  • High melting and boiling points
  • Soluble in polar solvents
  • Conduct electricity when molten or in aqueous solution
33
Q

Do all ionic compounds follow the general properties ?

A

No

34
Q

Describe the effect of ionic size on lattice enthalpy and melting point

A
  • Ionic radius increases
  • Attraction between ions decreases
  • Lattice enthalpy becomes less negative
  • Melting point decreases
35
Q

Describe the effect of ionic charge on lattice enthalpy and melting point

A
  • Ionic charge increases
  • Attraction between ions increases
  • Lattice enthalpy becomes more negative
  • Melting point increases
36
Q

Describe the effect of ionic size on hydration enthalpy

A
  • Ionic radius increases
  • Attraction between ion and water molecules decreases
  • Hydration energy less negative
37
Q

Describe the effect of ionic charge on hydration enthalpy

A
  • Ionic charge increases
  • Attraction with water molecules increases
  • Hydration energy becomes more negative
38
Q

Why is hydration enthalpy an inaccurate method of predicting solubility?

A

Many compounds with endothermic enthalpy changes of solution are soluble.

39
Q

Define entropy

A

A measure of the dispersal of energy within the chemicals in a chemical system

40
Q

What are the unit for entropy ?

A

J/K/mol

41
Q

How does entropy relate to physical states?

A

In order of size : gases > liquids > solids, for entropy values

42
Q

How are entropy, the dispersal of energy and disorder related ?

A

The greater the entropy, the larger the dispersal of energy and the greater the disorder

43
Q

What is a system said to be if it is very random ?

A
  • Energy is spread out more
  • Entropy change is positive
44
Q

What is a system said to be if it is not very random ?

A
  • Energy is concentrated
  • Entropy change is negative
45
Q

When does entropy generally increase ?

A

During changes of state because the particles become more random

46
Q

What is entropy like when there is an increase in gaseous molecules in the reaction ?

A

It is positive

47
Q

What is entropy like when there is a decrease in gaseous molecules in the reaction ?

A

It is negative

48
Q

Define standard entropy

A
  • The entropy of one mole of a substance under standard conditions
  • It is always positive
49
Q

How is an entropy change calculated for a reaction?

A

Change in entropy is the sum of the entropies of the products minus the sum of the entropies of the reactants

50
Q

How is an entropy change calculated for a reaction?

A

Change in entropy is the sum of the entropies of the products minus the sum of the entropies of the reactants

51
Q

What is feasibility?

A

Whether a reaction is able to happen and is energetically feasible (or spontaneous).

52
Q

What is the equation for free energy change?

A

ΔG = ΔH - TΔS

53
Q

What is the requirement for the free energy change such that a reaction is feasible?

A
  • ΔG < 0
  • A decrease in free energy.
54
Q

Even though a reaction may have a negative value for ΔG, why might the reaction not take place at room temperature?

A

High activation energy resulting in a very slow rate.

Chemistry (29 decks)

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