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Chemistry > Thermodynamics Part 1 > Flashcards

Thermodynamics Part 1 Flashcards

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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
Q

Why is the value for second IE always larger than value for first IE

A

stronger attraction- same protons but fewer electrons

+ve ion attracting -ve electrons

26
Q

First electron affinity

A

The enthalpy change when one mole of gaseous 1- ions are formed from one mole of gaseous atoms

27
Q

First electron affinity of chlorine

A

Cl(g) + e- > Cl-(g)

28
Q

Why is first electron affinity always expthermic

A

Energy is released when the nucleus of an atom attracts an electron

29
Q

Second electron affinity

A

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

30
Q

Equation to represent the second electron affinity of oxygen

A

O-(g) + e- > O2-(g)

31
Q

Why is second electron affinity always endothermic

A

energy is needed to overcome the repulsion between the electrons and anion (both negative)

32
Q

The perfect ionic model

A

Ions are perfect spheres with only electrostatic forces of attractive (no covalent character)

33
Q

When does the fact that experimental lattice enthalpies found using born haber cycles are usually different to the theoretical value provide evidence for

A

Some ionic compounds having covalent character

34
Q

What is the relationship between the closeness of the experimental and theoretical value and the degree of ionic bonding

A

The closer the two values the greater the degree of ionic bonding

35
Q

What must the energy produced when water surrounds the ions be the same as for a solid dissolves

A

The electrostatic forces of attraction between the ions

36
Q

First step in solid dissolving

A

Ionic lattice breaks down into gaseous ions

MX(s) > M+(g) + X-(g)

37
Q

Second step in solid dissolving

A

Hydration of gaseous ions

M+(g) + X-(g) > M+(aq) + X-(aq)

38
Q

What is the resulting enthalpy change when a solid dissolves known as

A

The enthalpy change of solution

39
Q

Enthalpy of solution

A

The enthalpy change when one mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution

40
Q

Equation to represent the enthalpy of solution of sodium chloride

A

NaCl(s) > Na+(aq) + Cl-(aq)

41
Q

Enthalpy of hydration

A

The enthalpy change when one mole of aqueous ions is formed from one mole of gaseous ions

42
Q

Equation to represent the enthalpy of hydration of sodium ions

A

Na+(g) > Na+(aq)

43
Q

Why are enthalpies of hydration always expthermic

A

Energy is released when the gaseous ions form bonds to water

44
Q

What are lattice enthalpy values a measure of

A

The strength of attraction between oppositely charged ions

45
Q

What affects how strong the forces of attraction between oppositely charged ions are

A

Charged density

46
Q

What two things affect charge density

A

Size of ion

Size of charge

47
Q

Why do lattice enthalpies become less expthermic NaCl> NaI

A
  • Cl- smaller ion
  • greater charge density
  • greater attraction, stronger ionic bonding
  • therefore enthalpy of lattice formation becomes more expthermic
48
Q

Why do lattice enthalpies become more exothermic NaCl > MgCl2 > MgO

A

As charges increase on ions, stronger attraction between oppositely charged ions, stronger ionic bonding therefore more exothermic enthalpy of lattice formation

49
Q

Why do hydration enthalpies become more exothermic I->Br->Cl-

A

Cl- smaller ion- greater charge density- greater attraction to water molecules

50
Q

Why does hydration enthalpy become more exothermic Na+>Mg2+>Al3+

A

As charge on ions increases, attraction with water molecules increases massively- mucb more exothermic hydration enthalpy

Chemistry (42 decks)

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