Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-Level Chemistry > Chapter 22 > Flashcards

Chapter 22 Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

Ionic bonds

A

Electrostatic attraction between oppositely-charged ions in the lattice structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Lattice Enthalpy

A

Measure of the strength of ionic bonding in a giant ionic lattice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Lattice Enthalpy DEFINITION

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Equation for KCl lattice Enthalpy?

A

K+ (g) + Cl- (g) -> KCl (s)
Gaseous ions -> solid ionic compounds
It is an EXOTHERMIC change and will always be negative as it involves bond formation (which releases energy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Depict lattice Enthalpy on a cycle?

A

It is a downwards arrow from gaseous ions to the ionic lattice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a born-Haber cycle?

A

Cannot be measured directly and must be calculated indirectly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Born-Haber route for KCl Route 1?

A

Elements in standard states -> gaseous atoms (endothermic - formation of gaseous atoms)
Gaseous atoms -> gaseous ions (endothermic - formation of gaseous ions)
Gaseous ions -> ionic lattice (LATTICE ENTHALPY - EXOTHERMIC)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Born Haber cycle Route 2?

A

Changing from standard state directly to the ionic lattice - this is the Enthalpy change of FORMATION - this is Exothermic (just one Enthalpy change)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Standard Enthalpy change of formation?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Standard Enthalpy change of atomisation? Give example for Cl2

A

Enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
1/2Cl2 (g) -> Cl(g)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Nature of Enthalpy change of atomisation?

A

Always endothermic as bonds are broken to form gaseous atoms ; when the element is a gas in its standard state, the standard Enthalpy change of atomisation = bond Enthalpy of bond being broken
Cl2(g) -> 2Cl(g) = +242kJ/mol
1/2 Cl2(f) -> Cl(g) = 121kJ/mol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

First ionisation energy?

A

Enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Na (g) -> Na+ (g) + e-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Nature of ionisation energies?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Electron affinity

A

Opposite of ionisation energy - measures the energy to GAIN electrons - first electron affinity is 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
Cl(g) + e- -> Cl- (g)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Nature of electron affinity

A

Exothermic because the electron being added is attracted in towards the nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Ionisation energy/electron affinity of NaCl?

A

Ionisation energy of Na to Na+ (endothermic) - release an electron
Electron affinity of Cl to Cl- (Exothermic) - gain that electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Second electron affinity?

A

With Oxygen - second electron affinities are endothermic… a second electron is being gained by a negative ion which repels the electron away so energy must be put in to force the negatively charged electron onto the negative ion
First electron affinity Exothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What happens when salt dissolves in water?

A

Water molecules are able to break up the giant ionic lattice structure and overcome the strong electrostatic attractions between oppositely charged ions - this is what happens when salt dissolves in water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Standard Enthalpy of solution

A

Enthalpy change that takes place when one mole of a solute dissolves in a solvent ; if the solvent is water the ions from the ionic lattice finish up surrounded with water molecules as aqueous ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Equation for standard Enthalpy change of solution of NaCl

A

Na+Cl- (s) + aq -> Na+ (aq) + Cl- (aq)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How can Enthalpy change of solution be determined experimentally?

A

Weigh a sample of the ionic lattice and pour a set amount of water into the plastic cup in the beaker (measure temperature) ; quickly tip all KCl into the water and stir until fully dissolved and the temperature no longer changes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Maths in experimentally determining Enthalpy change of solution

A

q = mc(change in temperature)
Where mass = mass of water (g) + mass of KCl
c = 4.18 (SHC)
Change in temperature
Figure out moles of KCl and then divide kJ of energy by moles

23
Q

What happens when a solid ionic compound dissolves in water?

A

Ionic lattice breaks up forming separate gaseous ions - opposite energy change from lattice energy which forms the ionic lattice from gaseous ions
Water molecules are attracted to and surround the ions - separate gaseous ions interact with polar water molecules to form hydrated aqueous ions… this energy change is called the Enthalpy change of hydration

24
Q

Enthalpy change of hydration

A

Enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions
NaCl (s) -> Na+(g) + Cl-(g) is endothermic you are breaking up the lattice (part of this is Enthalpy change of hydration (Exothermic or endothermic)
Exact opposite (just sign change) is formation of lattice

25
Q

What are three levels in Enthalpy change hydration cycles?

A

Gaseous ions
Aqueous ions
Ionic lattice

26
Q

Gaseous ions to ionic lattice

A

Lattice Enthalpy

27
Q

Gaseous ions to aqueous ions

A

Enthalpy change of hydration

28
Q

Ionic lattice to aqueous ions

A

Enthalpy change of solution

29
Q

Ionic compounds

A

High melting and boiling points
Soluble in polar solvents
Conduct electricity when molten or in aqueous solution

30
Q

Factors affecting lattice Enthalpy?

A

Effect of ionic size and effect of ionic charge

31
Q

Effect of ionic size on lattice Enthalpy?

A

Ionic radius increases
Attraction between ions decreases
Lattice energy less negative
Melting point decreases

32
Q

Effect of ion charge?

A

Ionic charge increases (best ratio 2:2 like CaO for example)
Attraction between ions increases
Lattice energy becomes more negative
Melting point increases

33
Q

Opposing effects with oppositely charged ions?

A

Na+ Mg2+ and Al3+
Increasing charge means more attraction
Decreasing size (more protons to same number of electrons)
S2- and Cl-
Increasing charge gives more attraction
Increasing size gives less attraction

34
Q

Uses of metal oxides?

A

Protective coating for the insides of furnaces

35
Q

What other factors needed for melting points?

A

Picking of ions

36
Q

Hydration Enthalpy factors?

A

Ionic size - as you go down the group, ionic radius increases and attraction between ion and water molecules decreases so hydration energy is less negative
Ionic charge - as you go along the period, ionic charge increases so attraction with water molecules increases and hydration energy becomes more negative

37
Q

Predicting solubility

A

If sum of hydration enthalpies is larger than the magnitude of lattice Enthalpy then the overall Enthalpy change will be Exothermic and the compound should dissolve

38
Q

What else does solubility depend on?

A

Temperature and entropy

39
Q

What is entropy?

A

A measure of disorder (S)

40
Q

Greater the entropy?

A

Greater the dispersal of energy and greater the disorder - tendency for energy to spread out
Greater the energy is spread out per kelvin per mole

41
Q

General entropy rules?

A

Solids have smallest entropies
Gases have greatest entropies

42
Q

If a system changes to become more random?

A

Energy is spread out more and entropy change is positive
Vice versa

43
Q

Solid to liquid to gas

A

Entropy increases

44
Q

Melting and boiling

A

Increases randomness and thus increases disorder and increases entropy

45
Q

Standard entropy?

A

Entropy of one mole of a substance under standard conditions (100kPa and 298 K) - they are ALWAYS POSITIVE and have units J/K/mol

46
Q

Calculating entropy changes?

A

Sum of Entropy of products - sum of entropy of reactants

47
Q

Feasibility?

A

A reaction can happen if products have a lower overall energy than the reactants - spontaneous is same as energetically feasible

48
Q

Free energy

A

Overall change in energy during a chemical reaction made of
1) Enthalpy change (heat transfer between chemical system and surroundings)
2) Entropy change at the temperature of the reaction ; dispersal of energy within the chemical system itself

49
Q

Gibbs equation

A

Enthalpy change with sureoundings - Temperature in Kelvin*Entropy of system

50
Q

If gibbs<0

A

Reaction is feasible

51
Q

Convert Celsius to Kelvin

A

+273

52
Q

What to remember in Gibbs energy?

A

Entropy should be divided by 1000 to become kJ/K/mol
As temperature increases, entropy becomes more significant

53
Q

Limitations of predictions made for feasibility

A

Free energy change is useful for predicting feasibility but many reactions have a negative Gibbs energy and do not seem to take place
BECAUSE IT DOES NOT TAKE INTO ACCOUNT ACTIVATION ENERGY - VERY SLOW RATE (NO ACCOUNT OF KINETICS OR RATE OF REACTION)

A-Level Chemistry (28 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions