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Thermodynamics Part 1 Flashcards

1
Q

What is the strength of the bonding in a lattice given by

A

It’s lattice enthalpy

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2
Q

What are the two ways to define lattice enthalpy

A
  • enthalpy of lattice dissociation

- enthalpy of lattice formation

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3
Q

Enthalpy of lattice dissociation

A

The enthalpy change to separate one mile of solid ionic compound into its gaseous ions

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4
Q

Why are enthalpies of lattice dissociation always endothermic

A

Bonds are being broken

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5
Q

What is the enthalpy of lattice dissociation a measure of

A

The strength of the electrostatic forces of attraction between ions, massive of the strength of the ionic bonding

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6
Q

Enthalpy of lattice formation

A

The enthalpy change when one mole of solid ionic compound is formed from its gaseous ions I

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7
Q

Why are enthalpies of lattice formation always endothermic

A

Bonds are being formed

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8
Q

How will the values for dissociation and formation be similar

A

They’ll be the same but have the opposite sign

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9
Q

Standard enthalpy of formation

A

The enthalpy change that occurs when one mole of a compound is formed from its constituent elements with all reactants and products in their standard states

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10
Q

Equation to represent the standard enthalpy of formation potassium chloride

A

K(s) + 1/2Cl2(g) > KCl(s)

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11
Q

What is the standard enthalpy of formation always in ionic compounds and why

A

Expthermic becaude energy is released when the compound is formed

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12
Q

Standard enthalpy of atomisation

A

The enthalpy change when one mole of gaseous atoms it formed from the element in its standard state

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13
Q

Equation to represent atomisation of chlorine

A

1/2 Cl2(g) > Cl (g)

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14
Q

What is atomisation always and why

A

Endothermic because energy is needed to form gaseous atoms

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15
Q

Bond enthalpy

A

The energy required to break one mole of a given covalent bond in the molecules in the gaseous state

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16
Q

Equation to represent the bond enthalpy of a Cl-Cl bond

A

Cl2(g)> 2Cl(g)

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17
Q

What is the relationship between the value for the bond enthalpy of a Cl-Cl bond and the value for the atomisation of chlorine

A

Bond enthalpy= 2xatomisation energy

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18
Q

Why are bond enthalpies always endothermic

A

It takes energy to break bonds

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19
Q

First ionisation energy

A

The energy needed to remove one mole of electrons from one mole of atoms in the gaseous state

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20
Q

Equation to represent the first ionisation energy of lithium

A

Li(g)>Li+ + e-

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21
Q

Why are first IEs always endothermic

A

It takes energy to remove an electron

22
Q

Second ionisation energy

A

The enthalpy change when one mole of gaseous 2+ ions are formed from one mole of gaseous 1+ ions

23
Q

Equation to represent the second IE of calcium

A

Ca+(g) > Ca2+(g) + e-

24
Q

Why is second IE always endothermic

A

It takes energy to remove an electron

25
Why is the value for second IE always larger than value for first IE
stronger attraction- same protons but fewer electrons +ve ion attracting -ve electrons
26
First electron affinity
The enthalpy change when one mole of gaseous 1- ions are formed from one mole of gaseous atoms
27
First electron affinity of chlorine
Cl(g) + e- > Cl-(g)
28
Why is first electron affinity always expthermic
Energy is released when the nucleus of an atom attracts an electron
29
Second electron affinity
The enthalpy change when one mole of gaseous 2- ions are formed from one mole of gaseous 1- ions
30
Equation to represent the second electron affinity of oxygen
O-(g) + e- > O2-(g)
31
Why is second electron affinity always endothermic
energy is needed to overcome the repulsion between the electrons and anion (both negative)
32
The perfect ionic model
Ions are perfect spheres with only electrostatic forces of attractive (no covalent character)
33
When does the fact that experimental lattice enthalpies found using born haber cycles are usually different to the theoretical value provide evidence for
Some ionic compounds having covalent character
34
What is the relationship between the closeness of the experimental and theoretical value and the degree of ionic bonding
The closer the two values the greater the degree of ionic bonding
35
What must the energy produced when water surrounds the ions be the same as for a solid dissolves
The electrostatic forces of attraction between the ions
36
First step in solid dissolving
Ionic lattice breaks down into gaseous ions MX(s) > M+(g) + X-(g)
37
Second step in solid dissolving
Hydration of gaseous ions M+(g) + X-(g) > M+(aq) + X-(aq)
38
What is the resulting enthalpy change when a solid dissolves known as
The enthalpy change of solution
39
Enthalpy of solution
The enthalpy change when one mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution
40
Equation to represent the enthalpy of solution of sodium chloride
NaCl(s) > Na+(aq) + Cl-(aq)
41
Enthalpy of hydration
The enthalpy change when one mole of aqueous ions is formed from one mole of gaseous ions
42
Equation to represent the enthalpy of hydration of sodium ions
Na+(g) > Na+(aq)
43
Why are enthalpies of hydration always expthermic
Energy is released when the gaseous ions form bonds to water
44
What are lattice enthalpy values a measure of
The strength of attraction between oppositely charged ions
45
What affects how strong the forces of attraction between oppositely charged ions are
Charged density
46
What two things affect charge density
Size of ion Size of charge
47
Why do lattice enthalpies become less expthermic NaCl> NaI
- Cl- smaller ion - greater charge density - greater attraction, stronger ionic bonding - therefore enthalpy of lattice formation becomes more expthermic
48
Why do lattice enthalpies become more exothermic NaCl > MgCl2 > MgO
As charges increase on ions, stronger attraction between oppositely charged ions, stronger ionic bonding therefore more exothermic enthalpy of lattice formation
49
Why do hydration enthalpies become more exothermic I->Br->Cl-
Cl- smaller ion- greater charge density- greater attraction to water molecules
50
Why does hydration enthalpy become more exothermic Na+>Mg2+>Al3+
As charge on ions increases, attraction with water molecules increases massively- mucb more exothermic hydration enthalpy

Chemistry (42 decks)

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