Chapter 22

Question 1

Why are solid ionic compounds very stable?

Answer 1

1) strength of ionic bonds

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

Question 2

What does lattice enthalpy measure?

Answer 2

the strength of ionic bonding in a giant ionic lattice

Question 3

What is lattice enthalpy?

Answer 3

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

Question 4

K⁺(g) + Cl⁻(g) –>

Answer 4

KCl(s)

Question 5

Is lattice enthalpy endothermic or exothermic?

Answer 5

exothermic

Question 6

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

Answer 6

make

Question 7

Can lattice enthalpy be measured directly?

Answer 7

no

Question 8

What is route 1 of a Born-Haber cycle?

Answer 8

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

Question 9

What is route 2 of a Born-Haber cycle?

Answer 9

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

Question 10

What is the standard enthalpy change of formation, ΔfH?

Answer 10

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

Question 11

What is the standard enthalpy change of atomisation ΔatH?

Answer 11

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

Question 12

Is ΔatH endothermic or exothermic?

Answer 12

endothermic

Question 13

Why is ΔatH endothermic?

Answer 13

bonds are broken to form gaseous atoms

Question 14

What is the first ionisation energy, ΔIEH?

Answer 14

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

Question 15

Are ionisation energies endothermic or exothermic?

Answer 15

endothermic

Question 16

Why are ionisation energies endothermic?

Answer 16

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

Question 17

What is the first electron affinity, ΔEAH?

Answer 17

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

Question 18

Are first electron affinities endothermic or exothermic?

Answer 18

exothermic

Question 19

Why are first electron affinities exothermic?

Answer 19

the electron being added is attracted towards the nucleus

Question 20

Are second electron affinities endothermic or exothermic?

Answer 20

endothermic

Question 21

Why are second electron affinities endothermic?

Answer 21

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

Question 22

What is the standard enthalpy change of solution, ΔsolH?

Answer 22

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

Question 23

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

Answer 23

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

Question 24

Is the enthalpy change of solution endothermic or exothermic?

Answer 24

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

Question 25

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

Answer 25

1) ionic lattice breaks up | 2) water molecules are attracted to, and surround, the ions

Question 26

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

Answer 26

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

Question 27

What is the enthalpy change of hydration, ΔhydH?

Answer 27

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

Question 28

What are the properties of ionic compounds?

Answer 28

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

Question 29

What factors affect lattice enthalpy?

Answer 29

1) ionic size | 2) ionic charge

Question 30

How does ionic size affect lattice enthalpy down a group?

Answer 30

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

Question 31

How does ionic charge affect lattice across down a period?

Answer 31

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

Question 32

What does the magnitude of lattice energy indicate?

Answer 32

1) melting point of an ionic compound | 2) packing of ions in an ionic lattice

Question 33

What factors affect hydration enthalpies?

Answer 33

1) ionic size | 2) ionic charge

Question 34

How does ionic size affect lattice enthalpy down a group?

Answer 34

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

Question 35

How does ionic charge affect lattice enthalpy across a period?

Answer 35

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

Question 36

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

Answer 36

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

Question 37

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

Answer 37

1) overall energy change is exothermic | 2) compound should dissolve

Question 38

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

Answer 38

1) overall energy change is endothermic | 2) compound should not dissolve

Question 39

What do the reasons for solubility depend on?

Answer 39

1) temperature | 2) entropy

Question 40

What does entropy, S explain?

Answer 40

things that occur naturally

Question 41

The greater the entropy, the greater the...

Answer 41

1) dispersal of energy | 2) disorder

Question 42

What is the term entropy used for?

Answer 42

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

Question 43

What are the units of entropy?

Answer 43

J K⁻¹mol⁻¹

Question 44

What are the general entropies with regard to different states?

Answer 44

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

Question 45

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

Answer 45

higher

Question 46

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

Answer 46

positive

Question 47

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

Answer 47

negative

Question 48

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

Answer 48

increase

Question 49

Do reactions that produce gases increase or decrease entropy?

Answer 49

increase

Question 50

Why do reactions that produce gases increase entropy?

Answer 50

1) increases disorder of particles | 2) energy is spread out more - change in entropy is positive

Question 51

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

Answer 51

decrease

Question 52

What is the standard entropy S of a substance?

Answer 52

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

Question 53

Are standard entropies positive or negative?

Answer 53

positive

Question 54

entropy change of a reaction =

Answer 54

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

Question 55

What is feasibility used to describe?

Answer 55

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

Question 56

What is the free energy change, ΔG?

Answer 56

overall energy change during a chemical reaction

Question 57

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

Answer 57

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

Question 58

ΔG =

Answer 58

ΔH - TΔS