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Chemistry > 5.2.1: Lattice enthalpy > Flashcards

5.2.1: Lattice enthalpy Flashcards

1
Q

Define lattice enthalpy

A

Enthalpy change for the formation of 1 mole of ionic lattice from gaseous ions under standard conditions

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2
Q

What is lattice enthalpy a measure of ?

A

Strength of ionic bonding in giant ionic lattice structures

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3
Q

Why are lattice enthalpies theoretical values ?

A

Gaseous ions can’t exist under standard conditions

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4
Q

What is a feature of lattice enthalpy practically ?

A

Can’t be measured directly

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5
Q

What does a more negative lattice enthalpy indicate ?

A

Stronger ionic bond

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6
Q

Define enthalpy change of formation

A

Enthalpy change when 1 moles of a compound is formed from its constituent elements in their standard states under standard conditions

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7
Q

Is Lattice enthalpy exothermic or endothermic ?

A

Exothermic

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8
Q

Is enthalpy change of formation usually endothermic or exothermic ?

A

Exothermic

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9
Q

Define enthalpy change of first ionisation energy

A

Enthalpy change when 1 mole of gaseous 1+ ions are made from 1 moles of gaseous atoms by loss of an electron

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10
Q

Is enthalpy change of first ionisation energy endothermic or exothermic ? why?

A

Endothermic as electrons are removed

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11
Q

Define enthalpy change of second ionisation energy

A

Enthalpy change when 1 mole of gaseous 2+ ions are made from 1 mole of gaseous atoms by loss of electrons

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12
Q

Is enthalpy change of second ionisation energy exothermic or endothermic ? why?

A

Endothermic (more than first ionisation energy) as ion is smaller meaning greater attraction from nucleus

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13
Q

Is first electron affinity exothermic or endothermic ?

A

Exothermic

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14
Q

Is second electron affinity exothermic or endothermic ? why?

A

Endothermic as electrons have to overcome repulsion of -1 ion

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15
Q

Explain why the second electron affinity of oxygen is positive

A

Oxide ion and electron are both negative so energy is required to overcome repulsion

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16
Q

Is enthalpy change of atomisation exothermic or endothermic ? why?

A

Endothermic as more energy is required to break bonds than required to make them

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17
Q

Why is Na ionised before Cl ?

A

You need to lose an electron from an atom before it can be gained

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18
Q

Define enthalpy change of solution

A

Energy change when 1 moles of a solute dissolves in a water

19
Q

Is enthalpy change of solution exothermic or endothermic ? why ?

A

Exothermic or endothermic depending on size of lattice enthalpy and enthalpy change of hydration

20
Q

Define enthalpy change of hydration

A

Enthalpy change when 1 moles of gaseous ions dissolves in water to form 1 mole of aqueas ions

21
Q

Is enthalpy change of hydration exothermic or endothermic ? why ?

A

Can be both as to dissolve bonds must break (endothermic) and new bonds must form between solvent and substance (exothermic)

22
Q

How can enthalpy change of solution be measured practically ? Use KCl

A
  • Weigh sample of KCl
  • Pour 25cm^3 distilled water into plastic cup in beaker with measuring cylinder
  • Measure water temp. to nearest 0.5 degrees
  • Tip KCl into water, stir with thermometer until KCl has dissolved and there are no further temperature changes
  • Use q =mc delta T
  • Divide q by moles
23
Q

What does a larger change on an ion mean for ionic substances ?

A

Larger charge = stronger electrostatic attraction between ions = more energy to break forces = higher mp + bp

24
Q

What does a smaller size of ion/ smaller atomic radius mean for ionic substances ?

A

Smaller ion = stronger electrostatic attraction between ions = pack closer together = more energy to break forces = high mp + bp

25
Q

What does a smaller ion and higher charge mean ?

A

HIGHER CHARGE DENSITY

26
Q

How does ionic size down a group affect lattice enthalpy ?

A
  • Ionic radius increases
  • Attraction between ions decreases
  • Lattice energy is less negative
  • Melting point of ionic compound decreases
27
Q

How does ionic charge affect lattice enthalpy ?

A
  • As ionic charge increases…
  • Attraction between ions increases
  • Lattice enthalpy becomes more negative
  • Melting point increases
28
Q

Why are metal oxides used as protective coating inside furnaces ?

A

Because they have a very negative lattice enthalpy so have a very high melting point

29
Q

How does ionic size down a group affect enthalpy changes of hydration ?

A
  • Ionic radius increases
  • Attraction between ion and water molecules decreases
  • Enthalpy change of hydration is less negative
30
Q

How does ionic charge affect enthalpy changes of hydration ?

A
  • As ionic charge increases ..
  • Attraction with water molecules increases
  • Enthalpy change of hydration is more negative
31
Q

What are the 2 factors which determine solubility ?

A

Temperature and entropy

32
Q

What means a compound should be soluble and are there exceptions ?

A

If sum of enthalpies of hydration are larger than lattice enthalpy then overall energy change is exothermic so compound should dissolve. HOWEVER, some endothermic compounds are soluble !

33
Q

Why is the lattice enthalpy of sodium oxide more exothermic than potassium oxide ?

A

Ions are smaller in Na+ creating a stronger attraction to O2-

34
Q

What are the units for q ?

A

J or KJ

35
Q

Predict how enthalpy changes of F- and Cl- would differ

A
  • F- has a smaller atomic radius so has a stronger nuclear attraction than Cl- meaning it has a more negative enthalpy change
  • F- is a smaller sized ion causing a greater attraction to H20
36
Q

What sign follows a enthalpy change of solution practical calculation ?

A

-

37
Q

How do you calculate % uncertainty ?

A

Uncertainty divided by measured value x100

38
Q

How does a larger volume of water affect temperature changes ?

A

Decreases temperature change as same heat is spread over a large volume of water

39
Q

How does a larger volume of water affect enthalpy change of solution ?

A

Stays the same as same energy is released per molecule of.. and ratio of energy produced to moles is the same

40
Q

Why does NaBr (smaller atomic radii) have a higher melting point than KI ?

A

NaBr has greater attraction from smaller ions which have a greater charge density. More energy needed to break ionic bonds and overcome attraction between ions

41
Q

How does doubling the mass of CaCl2 affect temperature change and enthalpy change of solution

A
  • Temperature change doubles as twice the energy is produced in the same volume
  • enthalpy change of solution stays the same as ratio of energy produced to moles is the same
42
Q

Why is the first ionisation energy of calcium endothermic ?

A

Because energy is needed to overcome the force of attraction between outer electrons and nucleus

43
Q

What state is iodine ?

A

Solid

Chemistry (38 decks)

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