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OCR A level Chemistry > Lattice enthalpy > Flashcards

Lattice enthalpy Flashcards

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1
Q

Define lattice enthalpy

A

The enthalpy change associated with the formation of one mole of an IONIC compound from its gaseous ions under standard conditions

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2
Q

What is the symbol for lattice enthalpy

A

ΔLeHϴ

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3
Q

What symbol accompanies lattice enthalpy?

A

-

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4
Q

Why is lattice enthalpy always negative?

A

It represents the formation of bonds which releases energy and so is exothermic

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5
Q

Write an equation to represent the lattice enthalpy of NaCL

A

Na+ (g) + Cl- (g) —-> NaCl(s)

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6
Q

What is the definition of enthalpy of formation?

A

The enthalpy change that accompanies the formation of one mole of a substance from its elements under standard conditions with all reactants and products in their standard states

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7
Q

What is the definition of 1st ionisation energy?

A

The amount of energy required to remove one electron from each atom in one mole of gaseous atoms OF AN ELEMENT to form one mole of gaseous 1+ ions

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8
Q

Write an equation for 1st ionisation energy

A

Na(g) —–> Na+ (g) + e-

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9
Q

What is the sign of ionisation energy?

A

+

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10
Q

Why is ionisation always positive?

A

Energy is required to pull the electron being removed away from the nucleus

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11
Q

As more electrons are removed what happens to the value of IE and why?

A

The value increases
As more electrons are removed the remaining electrons are pulled in closer to the nucleus and so more energy is required to remove the electrons

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12
Q

What is the definition of enthalpy of atomisation?

A

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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13
Q

What is the sign for enthalpy of atomisation?

A

Always +

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14
Q

Why is the sign of enthaply of atomisation always +?

A

Bonds holding atoms together in their standard states must be broken

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15
Q

What is the definition of 1st electron affinity?

A

Th energy change that accompanies the addition of one electron to each atom in one mole of atoms of an element on gaseous form to form one mole of gaseous 1- ions

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16
Q

Is 1st Electron affinity exothermic?

A

Yes

17
Q

Why is 1st electron affinity exothermic?

A

An electron is being added and will be attracted to the nucleus

18
Q

Are subsequent electron affinities exothermic?

A

No

19
Q

Why are subsequent electron affinities endothermic?

A

Electrons are being added to a negatively charged ion, and it is necessary to overcome the repulsion

20
Q

From the bottom left hand side round to the bottom right hand side, what is the order of enthalpy changes?

A
  • Formation
  • Atomisation
  • 1st ionisation energy
  • any subsequent ionisation energies
  • atomisation
  • 1st electron affinity
  • any subsequent electron affinities
  • lattice enthalpy
21
Q

Define enthalpy of hydration

A

The enthalpy change when one mole of isolated gaseous ions is dissolved in water under standard conditions

22
Q

Define enthalpy change of solution

A

The enthalpy change when one mole of a substance is completely dissolved in water under standard conditions

23
Q

What is the symbol for enthalpy change of solution?

A

ΔsolHϴ

24
Q

What is the symbol for enthalpy change of hydration?

A

ΔhydHϴ

25
Q

Is the enthalpy change of solution endothermic or exothermic?

A

Either

26
Q

Is the enthalpy change of hydration endothermic or exothermic?

A

Exothermic

27
Q

Why is the enthalpy change of hydration exothermic?

A

Bonds are being formed between ions and water

28
Q

Are the lattice enthalpies of larger ions more or less exothermic?

A

Less

29
Q

Why do larger ions have a less exothermic lattice enthalpy?

A
  • the electrostatic attraction between the ions is weaker

- because the ions have a lower charge density

30
Q

How is charge density calculated?

A

charge/volume

31
Q

Are the lattice enthalpies of more highly charge ions more or less exothermic?

A

More

32
Q

Why do more highly charged ions have a more exothermic lattice enthalpy?

A
  • the electrostatic attraction between the ions is stronger

- because the charge density is higher

33
Q

Do smaller ions have a more or less exothermic value of enthalpy of hydration?

A

More

34
Q

Why do smaller ions have a more exothermic enthalpy of hydration?

A
  • smaller ions have larger charge densities

- so attract water molecules more strongly

35
Q

Do ions with a smaller charge have more or less exothermic enthalpies of hydration?

A

Less

36
Q

Why do ions with a smaller charge have a less exothermic enthalpy of hydration?

A
  • the ions have smaller charge densities

- so they cannot attract water molecules as strongly

OCR A level Chemistry (30 decks)

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