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Oceans Flashcards

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1
Q

How is the strength of ionic attraction measured?

A

Lattice enthalpy

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2
Q

What is the lattice enthalpy?

A

Enthalpy change when one mole of solid is formed from its gaseous ions

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3
Q

Are lattice enthalpies positive or negative, and why?

A

Negative- bond making

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4
Q

How do you break down a lattice?

A

Put in energy equal to the negative LEH (this becomes positive as you are putting energy in)

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5
Q

What factors affect lattice enthalpy?

A

Ionic charge
Ionic radii

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6
Q

What makes a lattice enthalpy more negative?

A

Increased ionic charge
Decreased ionic radii

Charge density increases, and so increases attraction, increasing the bond strength

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7
Q

Bond breaking/making

A

Breaking - endo +
Making - exo -

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8
Q

How does hydration occur?

A

Ion-dipole interactions
Positive ions surrounded by negative end of water molecule
Negative ions surrounded by positive end of water molecule

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9
Q

What does weak/extensive hydration mean?

A

Ions are weakly/strongly bound to water molecules

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10
Q

How does charge density of an ion affect its hydration?

A

Larger charge density increases the number of water molecules it can attract
A small ion can become large as a hydrated ion

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11
Q

How can energy be provided to break the lattice enthalpy?

A

Formation of bonds between ions and water molecules

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12
Q

Why can’t hydration enthalpy be used to achieve enough energy to break a lattice?

A

Water molecules have strong hydrogen bonds, so breaking these bonds so they can reform around the ion also requires energy

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13
Q

What is the enthalpy change of hydration?

A

Strength of attractions between ions and water molecules
Enthalpy change of a formation of solution from one mole of gaseous ions

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14
Q

Lattice enthalpy of NaCl equation

A

Na+(g) + Cl-(g) –> NaCl(s)

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15
Q

Hydration enthalpy of sodium equation

A

Na+(g) + aq –> Na+(aq)

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16
Q

Is the value of hydration enthalpy negative or positive, and why?

A

Negative- hydration is exothermic as bonds are being formed

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17
Q

What is enthalpy of solvation?

A

Using solvents other than water (eg ethanol)
Enthalpy change when 1 mol of ionic substance dissolves in the solvent to form a solution

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18
Q

What is enthalpy change of solution?

A

Difference in enthalpy between
- hydration enthalpy
- lattice enthalpy
One mol of solute dissolves to form a very dilute solution

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19
Q

What is the equation for enthalpy change of solution?

A

solutionH = hydH (cation) + hydH (anion) - leH

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20
Q

Enthalpy cycle- what is the original and alternative route for solution enthalpy?

A

Original: ionic lattice + solvent –(solutionH)–> solution

Alternative: ionic lattice + solvent –(-leH)–> gaseous ions + solvent –(hydH of cation+anion)–> solution

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21
Q

What does a negative enthalpy solution mean?

A

Hydration provides more energy than is needed to break the lattice
Solid will dissolve

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22
Q

What does a positive enthalpy of solution mean?

A

Hydration does not provide as much energy as is needed to break up the lattice
Solute does not dissolve

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23
Q

What does a slightly positive enthalpy of solution mean?

A

Hydration doesn’t provide exact energy but solute still dissolves

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24
Q

What are examples of greenhouse gases and where are they found?

A

CO2 and methane
Troposphere

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25
Q

What 2 things occur when IR is absorbed by greenhouse gases?

A

1) Increases vibrational energy of gases; vibrational energy can be transferred to other molecules by collision; increases kinetic energy- raising temp of air

2) Some IR re-emitted to earth, some to space

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26
Q

What is the most abundant greenhouse gas in the atmosphere?

A

Water vapour

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27
Q

What is the IR window?

A

The wavelengths of IR that water vapour does not absorb

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28
Q

Which gas absorbs wavelengths of light in the IR window?

A

CO2

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29
Q

How is the temperature of the earth being increased by increasing levels of CO2?

A

More CO2
More wavelengths of IR window absorbed- increasing temp
Increasing temp = more water vapour

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30
Q

What is an acid?

A

H+/proton donor

31
Q

What is a base?

A

H+/proton acceptor

32
Q

What is a conjugate acid-base pair?

A

HA (conj. acid) –> H+ + A- (conj. base)

33
Q

Water acting as a base

A

HCl + H2O –> H3O+ + Cl-

34
Q

Water acting as an acid

A

H2O + NH3 –> OH- + NH4+

35
Q

What is the equation for pH?

A

-log10 [H+(aq)]

36
Q

What is a strong acid?

A

Strong tendency to donate H+
Dissociate completely in aq

37
Q

Equations for dissociation of a strong acid

A

HA + H2O –> H3O+ + A-
Water is in excess:
HA –> H+ + A-

38
Q

Examples of strong acids

A

HCl
H2SO4

39
Q

What is a weak acid?

A

Tendency to donate H+ is weaker
Does not dissociate completely in water

40
Q

Equation for weak acids

A

HA <–> H+ + A-

41
Q

Example of a weak acid

A

Ethanoic acid (CH3COOH)

42
Q

Equilibrium in terms of strength of acid

A

Weak = left
Strong = right

43
Q

How to calculate pH of a strong acid

A

pH = -log10 [H+]

44
Q

How to calculate [H+] of a strong acid

A

10^-pH

45
Q

How to calculate pH of a weak acid

A

Ka = [H+][A-] / [HA]

46
Q

What are the 2 assumptions made about [H+] of weak acids?

A

1) [H+] = [A-]
Water is another source of [H+]
Produces far fewer H+ than a weak acid, neglecting ionisation of water has no effect

2) Amount of HA at equilibrium = amount of HA put into solution
Neglect H+ lost as weak acids dissociate very little

47
Q

pKa equation

A

pKa = -log10 Ka

48
Q

What is pKa?

A

Logarithmic scale as values for Ka of weak acids is very small

49
Q

How do you calculate pH of strong alkali?

A

1) Equation
2) Ka equation
3) Kw equation

50
Q

pH of strong alkali- equation (1)

A

H2O <–> H+ + OH-

51
Q

pH of strong alkali- Ka equation (2)

A

Ka = [H+][OH-] / [H2O]

52
Q

pH of strong alkali- Kw equation (3)

A

Water is in excess
Kw = [H+][OH-]

53
Q

What is a buffer?

A

Solutions that resist changes in pH despite the addition of small quantities of acid/alkali

54
Q

What are buffer solutions made from?
Examples

A

A weak acid/base and one of its salts

Ethanoic acid + sodium ethanoate
Ammonia + ammonium chloride

55
Q

Equation for action of a buffer solution

A

HA <–> H+ + A-

56
Q

What are the assumptions made about buffers to explain why they resist changes in pH?

A

1) All A- comes from the salt
Weak acid supplies very few A- in comparison to salt

2) Almost all HA remains unchanged

57
Q

What happens when H+ is added to a buffer solution?

A

A- reacts with extra H+
Forms HA and water
Removes H+
Reestablish pH

58
Q

What happens when OH- is added to a buffer solution?

A

H+ removed by OH-
H+ regenerated by HA

59
Q

Buffer calculation equation

A

Ka = [H+] x [salt]/[acid]

60
Q

What can be used to measure ‘insoluble’ ionic solids?

A

Kc - equilibrium constant

61
Q

Why is equilibrium equation different for ‘insoluble’ ionic solids?

A

Adding more solid does not cause equilibrium to shift towards product
Solution is saturated at that temp
Doesn’t affect amount of solid present
Solubility product equation

62
Q

What is the solubility product equation?

A

Ksp (solid) = [+][-]

63
Q

What is the solubility product constant?

A

Conditions for equilibrium between sparingly soluble solid + saturated solution

64
Q

Using Ksp to predict if a precipitate will form

A

[+][-] = more than Ksp = will precipitate
[+][-] = less or equal to Ksp = ions stay in solution

65
Q

What is entropy?

A

Randomness of a system, mathematically calculated
Ways that energy can be arranged between particles

66
Q

What does +/- entropy mean?

A

Positive = products more disordered than reactants
Negative = reactants more disordered than products

67
Q

What are the units for entropy?

A

J K-1mol-1

68
Q

What causes a higher entropy?

A

More spread out molecules
Energy shared among more molecules

69
Q

How to predict if a change is feasible?

A

TotalS must be positive

70
Q

What is the equation for total entropy change?

A

TotalS = sysS - surrS

71
Q

How do you calculate entropy of a system?

A

Entropy of products - entropy of reactants

72
Q

What is the equation for surrS?

A

-ΔH/T

73
Q
A

Chemistry (9 decks)

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