A2- Born-Haber COPY Flashcards

1
Q

What is meant by the term ‘enthalpy change of hydration’?

A

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

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2
Q

What is the definition of ‘enthalpy of lattice formation’?

A

the enthalpy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions

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3
Q

Why is enthalpy lattice of formation exothermic?

A

because it is equal to the formation of an electrostatic force between oppositely charged ions (ionic bond)

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4
Q

Write an equation equal to the lattice formation enthalpy of calcium fluoride

A

Ca2+(g) + 2F-(g) –> CaF2(s)

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5
Q

What 2 factors impact the size/strength of the enthalpy change of lattice formation?

A
  • size of the ions (larger ions have weaker forces)
  • charge of the ions (higher charges = stronger forces)
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6
Q

The lattice enthalpy of sodium chloride is -787 kJ mol -1 . Predict a value for the enthalpy change of lattice dissociation for sodium chloride. Explain your answer.

A

+ 787 kJ mol -1 . Lattice dissociation is the opposite enthalpy change of lattice formation and is endothermic due to breaking and ionic bond between Na + and Cl - ions

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7
Q

What is meant by the term ‘enthalpy change of atomisation’?

A

the enthalpy change when 1 mol gaseous atoms is formed from an element in its standard state under standard conditions

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8
Q

What is meant by the term ‘enthalpy change of bond dissociation’?

A

the enthalpy change when one mole of covalent bonds dissociate/break forming gaseous molecules.

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9
Q

What is meant by the term ‘1st ionisation enthalpy’?

A

The enthalpy change when one mole of gaseous atoms is converted into one mole of
gaseous ions with a 1+ charge and one mole of electrons

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10
Q

Why is 1st ionisation enthalpy an endothermic change?

A

because the electrostatic force of attraction between nucleus and electron is broken

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11
Q

Describe and explain the trend in ionisation enthalpy going down a group

A
  • decreases
  • atoms become larger
  • more electron shielding,
  • electrostatic force between nucleus and outer electron shell becomes weaker
  • easier to remove an electron.
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12
Q

Describe and explain the trend in ionisation enthalpy going across a period

A
  • increases
  • electron shielding remains constant
  • nuclear charge increases
  • stronger electrostatic force between nucleus and outer electron shell
  • harder to lose and electron.
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13
Q

What is meant by the term ‘1st electron affinity’?

A

The enthalpy change when one mole of electrons is added to one mole of gaseous atoms forming 1 mol gaseous ions with a charge of 1 –

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14
Q

What type of reaction is 1st electron affinity? why?

A

exothermic, because an electrostatic force (bond) is formed between nucleus and an electron

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15
Q

What type of reaction is 2nd electron affinity?

A

Endothermic
A bond is formed between nucleus and an electron, however there is a lot of repulsion to be overcome as and electron is being added to a negatively charged ion

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16
Q

What is lattice dissociation enthalpy?

A

the energy required to break apart an ionic lattice into its constituent ions in a gaseous state under standard conditions

17
Q

What does the +ve ion do when there is covalent character?

A

polarises the -ve ion, distorting its shape (it is not spherical)

18
Q

What would different experimental and theoretical values suggest?

A

(more) covalent character, less spherical ions
not obey perfect ionic model

19
Q

What data is used in Born-Haber cycles?

A

experimental

20
Q

What would similar experimental and theoretical values suggest?

A

similar to perfect ionic model

21
Q

What is meant by the perfect ionic model?

A

a theoretical model that assumes no covalent interactions and perfect spheres