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Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

What is the Born-Haber cycle? When is it used?

A

‘Special type of Hess’s law cycle’

- Used to calculate the lattice enthalpy of ionic compounds

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2
Q

Define atomisation

A

Formation of 1 mole of gaseous atoms

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3
Q

Define Ionisation

A

Formation of gaseous ions

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4
Q

Define standard enthalpy change of atomisation

A

The enthalpy change when 1 mole of gaseous atoms is formed under standard conditions

OR

The enthalpy change for this reaction:
Ca(s) ——> Ca(g)

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5
Q

Is atomisation ENDO or EXO. Why?

A

ENDO

because, bonds are being broken

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6
Q

Define standard enthalpy change of the 1st I.E

A

(1st I.E)
the enthalpy change of this reaction:
Ca(g) ——> Ca+ (g) + e-

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7
Q

Is the 1st I.E ENDO or EXO

Why?

A

ENDO

because, energy is needed to overcome the electrostatic attraction between the nucleus and the electron being removed

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8
Q

Define standard enthalpy change of the 2nd I.E

A

The enthalpy change for this reaction:

Ca+(g) ——> Ca2+(g) + e-

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9
Q

Is the 2nd I.E ENDO or EXO

Why?

A

MORE ENDO
because, more energy is needed to overcome the electrostatic attraction between the nucleus and the electron being removed

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10
Q

Define the standard enthalpy of the first electron affinity

A

The enthalpy change for this reaction:

F(g) + e- ——> F- (g)

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11
Q

Is the first electron affinity ENDO or EXO

Why?

A

EXO
because, there is an electrostatic force of attraction between the nucleus of the gaseous atom and the electron being added

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12
Q

Define the standard enthalpy of the second electron affinity

A

The enthalpy change for this reaction:

O-(g) + e- ——> O2- (g)

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13
Q

Is the second electron affinity ENDO or EXO

Why?

A

ENDO
because energy is needed to overcome the repulsion between the negatively charged gaseous ion and the negatively charged electron being added

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14
Q

Define Enthalpy of Lattice Formation

A

The enthalpy change when 1 mole of an ionic solid is formed from the gaseous ions under standard conditions

OR

the enthalpy change for this reaction:
K+(g) + F-(g) ——> KF(s)

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15
Q

Is the lattice of formation ENDO or EXO

Why?

A

EXO

because, there is a strong electrostatic force of attraction between the oppositely charged ions

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16
Q

Define Enthalpy of Lattice Dissociation

A

The enthalpy change when 1 mole of an ionic solid lattice is broken to form the separate gaseous ions under standard conditions.

OR

The enthalpy change for this reaction:

KF(s) ——> K+(g) + F-(g)

17
Q

Is the lattice of dissociation ENDO or EXO

Why?

A

ENDO

because, energy is needed to break the electrostatic force of attraction between the oppositely charged ions

18
Q

What 2 factors affect Lattice enthalpy

A
  • charge of ions

- Size/ radius of ion

19
Q

What do you call lattice enthalpy values from Born- Harber cycles

A

Experimental lattice energies

20
Q

What are theoretical lattice energy values

A

Values calculated from the ‘perfect ionic model’

21
Q

Name the 2 main assumptions of the ‘perfect ionic model’

A
  • The ions are perfectly spherical /(they are point charges)
  • The compound is 100% ionic. There is no distortion or polarisation of the ions (no covalent character present)
22
Q

Define the enthalpy change of solution

A

The enthalpy change when 1 mole of an ionic solid lattice is dissolved completely in water under standard conditions

OR

The enthalpy change for this reaction:
KCl(s) ——> K+(aq) + Cl-(aq)

23
Q

When an ionic solid is dissolved in water, which 2 thermodynamic processes are involved

A

-Lattice Dissociation
The ionic solid lattice is broken into the gaseous ions

-Hydration
The gaseous ions are converted into aqueous ions

24
Q

What is the equation for the 🔺H(sol) ?

A

🔺H(sol)

= lattice dissociation + 🔺H(hyd)

25
Q

Define the enthalpy change of Hydration

A

The enthalpy change when 1 mole of aqueous ions is formed from 1 mole of gaseous ions under standard conditions

OR

The enthalpy change for this reaction:
Na+ (g) ——> Na+(aq)

26
Q

Is the enthalpy of hydration ENDO or EXO

Why?

A

EXO

because of the strong electrostatic attraction between the ion and the diapoles in water

27
Q

What 2 factors affect the enthalpy of hydration?

A
  • Size of ion

- Charge of ion

28
Q

What does it mean if an ion has a higher ‘charge density’

A

SMALLER ion

HIGHER charge

29
Q

Define what it means for a reaction to be spontaneous/ ‘feasible’

A

Can occur freely/ of it’s own accord

30
Q

What is Entropy and give it’s units

A

‘The measure of the degree of disorder in a reaction’
UNITS: Jk-1 mol-1
J= joules
K= kelvin

31
Q

Why is the entropy of elements not zero?

A

Entropy is measured at 298K

- the particles still have some energy to distribute (still moving)

32
Q

Define the state of ‘perfect/ maximum order’

A

The state of a substance when the particles are stationary (only occurs at 0K)

33
Q

What does a graph showing entropy against temperature show?

A

Entropy increases as temperature increases
A change in state leads to a BIG INCREASE in entropy
Boiling results in a bigger increase in entropy than melting

34
Q

What is the equation for the entropy change of surroundings

A

🔺S = (-)🔺H / T

35
Q

What is the 2nd law of thermodynamics

A

For a spontaneous reaction

🔺S total must be positive

36
Q

What is the equation for ‘Gibbs free energy change’

A

🔺G = 🔺H - T🔺S

37
Q

Why might a reaction with negative GFEC not occur spontaneously and give solutions

A

Rate is too slow

  • Add a catalyst
  • Increase the temperature
38
Q

What is the equation for the entropy change of a system

A

entropy change of (products) - entropy change of (reactants)

Chemistry (4 decks)

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