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Chemistry OCR A-Level > Chapter 22 > Flashcards

Chapter 22 Flashcards

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1
Q

Why are solid ionic compounds very stable?

A

1) strength of ionic bonds

2) electrostatic attractions between oppositely-charged ions in ionic lattice

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2
Q

What does lattice enthalpy measure?

A

the strength of ionic bonding in a giant ionic lattice

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3
Q

What is lattice enthalpy?

A

the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

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4
Q

K⁺(g) + Cl⁻(g) –>

A

KCl(s)

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5
Q

Is lattice enthalpy endothermic or exothermic?

A

exothermic

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6
Q

Does lattice enthalpy break or make ionic bonds from separate gaseous ions?

A

make

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7
Q

Can lattice enthalpy be measured directly?

A

no

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8
Q

What is route 1 of a Born-Haber cycle?

A

1) formation of gaseous atoms
2) formation of gaseous ions
3) lattice formation

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9
Q

What is route 2 of a Born-Haber cycle?

A

converting the elements in their standard states directly to the ionic lattice - ΔfH

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10
Q

What is the standard enthalpy change of formation, ΔfH?

A

the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

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11
Q

What is the standard enthalpy change of atomisation ΔatH?

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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12
Q

Is ΔatH endothermic or exothermic?

A

endothermic

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13
Q

Why is ΔatH endothermic?

A

bonds are broken to form gaseous atoms

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14
Q

What is the first ionisation energy, ΔIEH?

A

the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

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15
Q

Are ionisation energies endothermic or exothermic?

A

endothermic

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16
Q

Why are ionisation energies endothermic?

A

energy is required to overcome the attraction between a negative electron and the positive nucleus

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17
Q

What is the first electron affinity, ΔEAH?

A

the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

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18
Q

Are first electron affinities endothermic or exothermic?

A

exothermic

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19
Q

Why are first electron affinities exothermic?

A

the electron being added is attracted towards the nucleus

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20
Q

Are second electron affinities endothermic or exothermic?

A

endothermic

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21
Q

Why are second electron affinities endothermic?

A

1) a second electron is being gained by a negative ion - repels the electron away
2) energy must be put in to force the negatively-charged electron onto the negative-ion

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22
Q

What is the standard enthalpy change of solution, ΔsolH?

A

the enthalpy change that takes place when one mole of a solute dissolves in a solvent

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23
Q

What happens with the standard enthalpy change of solution, ΔsolH is the solvent is water?

A

the ions from the ionic lattice finish up surrounded with water molecules as aqueous ions

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24
Q

Is the enthalpy change of solution endothermic or exothermic?

A

either depending on relative sizes of lattice enthalpy + enthalpy changes of hydration

25
Q

What processes take place when a solid ionic compound dissolves in water?

A

1) ionic lattice breaks up

2) water molecules are attracted to, and surround, the ions

26
Q

What energy changes take place when a solid ionic compound dissolves in water?

A

1) ionic lattice is broken forming separate gaseous ions
2) separate gaseous ions interact with polar water molecules to form hydrated aqueous ions - enthalpy change of hydration

27
Q

What is the enthalpy change of hydration, ΔhydH?

A

the enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

28
Q

What are the properties of ionic compounds?

A

1) high melting + boiling points
2) soluble in polar solvents
3) conduct electricity when molten/in aqueous solution

29
Q

What factors affect lattice enthalpy?

A

1) ionic size

2) ionic charge

30
Q

How does ionic size affect lattice enthalpy down a group?

A

1) ionic radius increases
2) attraction between ions decreases
3) lattice energy less negative
4) melting point decreases

31
Q

How does ionic charge affect lattice across down a period?

A

1) ionic charge increases
2) attraction between ions increases
3) lattice energy becomes more negative
4) melting point increases

32
Q

What does the magnitude of lattice energy indicate?

A

1) melting point of an ionic compound

2) packing of ions in an ionic lattice

33
Q

What factors affect hydration enthalpies?

A

1) ionic size

2) ionic charge

34
Q

How does ionic size affect lattice enthalpy down a group?

A

1) ionic radius increases
2) attraction between ion and water molecules decreases
3) hydration energy less negative

35
Q

How does ionic charge affect lattice enthalpy across a period?

A

1) ionic charge increases
2) attraction with water molecules increases
3) hydration energy becomes more negative

36
Q

What has to happen to dissolve an ionic compound in water?

A

the attraction between the ions in the ionic lattice must be overcome

37
Q

What does it mean when the sum of hydration enthalpies is larger than the magnitude of the lattice enthalpy?

A

1) overall energy change is exothermic

2) compound should dissolve

38
Q

What does it mean when the sum of hydration enthalpies is smaller than the magnitude of the lattice enthalpy?

A

1) overall energy change is endothermic

2) compound should not dissolve

39
Q

What do the reasons for solubility depend on?

A

1) temperature

2) entropy

40
Q

What does entropy, S explain?

A

things that occur naturally

41
Q

The greater the entropy, the greater the…

A

1) dispersal of energy

2) disorder

42
Q

What is the term entropy used for?

A

the dispersal of energy within the chemicals making up the chemical system

43
Q

What are the units of entropy?

A

J K⁻¹mol⁻¹

44
Q

What are the general entropies with regard to different states?

A

1) solids = smallest entropies
2) liquids = greater entropies
3) gases = greatest entropies

45
Q

Do systems that are more chaotic have a higher or lower entropy value?

A

higher

46
Q

If a system becomes more random, is the entropy change positive or negative?

A

positive

47
Q

If a system becomes less random, is the entropy change positive or negative?

A

negative

48
Q

Does melting/boiling increase or decrease the randomness of particles?

A

increase

49
Q

Do reactions that produce gases increase or decrease entropy?

A

increase

50
Q

Why do reactions that produce gases increase entropy?

A

1) increases disorder of particles

2) energy is spread out more - change in entropy is positive

51
Q

Do reactions that result in a decrease of gas molecules increase or decrease entropy?

A

decrease

52
Q

What is the standard entropy S of a substance?

A

the entropy of one mole of a substance, under standard conditions

53
Q

Are standard entropies positive or negative?

A

positive

54
Q

entropy change of a reaction =

A

sum of standard entropies of products - sum of standard entropies of reactants

55
Q

What is feasibility used to describe?

A

whether a reaction is able to happen + is energetically feasible (spontaneous)

56
Q

What is the free energy change, ΔG?

A

overall energy change during a chemical reaction

57
Q

What two types of energy is the free energy change, ΔG made up of?

A

1) enthalpy change ΔH - heat transfer between chemical system + surroundings
2) entropy change at the temperature of the reaction TΔS - dispersal of energy within the chemical system

58
Q

ΔG =

A

ΔH - TΔS

Chemistry OCR A-Level (28 decks)

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