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A levels > Chemistry - EEE > Flashcards

Chemistry - EEE Flashcards

0
Q

What is the electron configuration of Chromium?

A

[Ar] 3d5, 4s1

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1
Q

What is the electron configuration of Copper?

A

[Ar] 3d10, 4s1

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2
Q

What is a transition element?

A

An element that forms one or more stable ions with a partially-filled d-subshell

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3
Q

Why is scandium not a transition element?

A

Its only stable ion is Sc3+, which has a configuration of [Ar] 3d0

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4
Q

Why is Zinc not a transition element?

A

Its only stable ion is Zn2+, which has a configuration of [Ar] 3d10

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5
Q

what are the 4 typical characteristics of transition metals?

A

1) Variable oxidation state in compounds
2) The metals and their compounds are often catalytically
3) Able to form a wide range of complex ions
4) form coloured compounds

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6
Q

Why do transition metals have variable oxidation states?

A

The energies of the 4s and 3d electrons are very similar

-> the elements can lose (or share) various number of electrons

when they form stable compounds

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7
Q

Why are transition metals good catalysts?

A

They are good at absorbing reactants on the metal suface

thereby weaking the bonding in the molecule and hence lowering the activation energy

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8
Q

Give examples of transition metals being used as catalysts

A

1) Catalytic Converters - Platinum, Rhodium, and Palladium
2) Haber Process - Iron metal

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9
Q

Why are transition metal compounds often catalytically active?

A

They can easily and reversibly change oxidation states

  • allows them to provide alternative reaction pathways in redox reactions
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10
Q

Give an example of a transition metal compound being used as as catalyst

A

Vanadium Oxide - Catalyses oxidation of SO2 to SO3 in the manufacture of sulphuric acid

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11
Q

What is a complex ion?

A

A metal ion bonded to a number of ligands by coordinate bonds (dative covalent bonds)

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12
Q

what is a ligand?

A

An ion or molecule with a lone pair of electrons which it donates to a central metal ion by forming a coordinate bond with it

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13
Q

In what 2 cases does the colour of a transition metal change?

A

1) When the oxidation state changes
2) When a complex ion with different ligands are formed

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14
Q

What is the colour of iron in:

1) [Fe(H2O)6]2+
2) [Fe(H2O)6]3+

A

1) 2+: Pale green
2) 3+: Yellow

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15
Q

What are the colours of the following ligands of cobalt:

1) [Co(H2O)6]2+
2) [CoCl4]2+

A

1) [Co(H2O)6]2+: Pink
2) [CoCl4]2+ : Blue

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16
Q

What colour are the following compounds of Copper?

1) [Cu(H2O)6]2+
2) [Cu(NH3)4(H2O)2]2+
3) [CuCl4]2-

A

1) [Cu(H2O)6]2+ : Blue
2) [Cu(NH3)4(H2O)2]2+ : Deep blue
3) [CuCl4]2- : Yellow

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17
Q

Write the equation of the reaction which is used as a test for the presence of Fe2+ ions, and the observation to confirm the reaction has occured

A

Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)

Green Precipitate

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18
Q

Write the equation of the reaction which is used as a test for the presence of Fe3+, and give the observation used as a positive result

A

Fe3+ (aq) + 3 OH- (aq) -> Fe(OH)3

Red/Brown Precipitate

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19
Q

Write the equation of the reaction which is used as a test for the presence of Co2+, and give the observation used as a positive result

A

Co2+ (aq) + 2OH- -> Co(OH)2 (s) Blue Precipitate

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20
Q

Write the equation of the reaction which is used as a test for the presence of Cu2+ , and give the observation used as a positive result

A

Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)

Blue precipitate

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21
Q

What are unidentate ligands?

A

Simple ligands which have a single point of attachment to the ion

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22
Q

What are Bidentate Ligands?

A

a Lignad with 2 lone pairs, each capable of forming a coordinate bond to a metal ion

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23
Q

what is the coordination number of an ion in a complex?

A

The number of ligand lone pairs that are bound to the ion - I.e. the number of co-ordinate bonds formed to the metal

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24
Q

What factor affects the co-ordination number of a compound?

A

Size of the ligands

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25
Q

What factor affects the shape of complex ions?

A

1) Size - large ligands and small ions favour tetrahedral geometry - less crowded

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26
Q

What is the bond angle in a tetrahedral complex ion?

A

109.5

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27
Q

what is the bond angle in a square planar complex ion?

A

90* or 180*

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28
Q

What are the bond angles in octahedral complex ions?

A

90* or 180*

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29
Q

Why may ligand substitution reaction occur?

A

1) One ligand can form stronger coordinate bonds to the metal ion than another
2) The substituting ligand is present in a higher concentration than the other

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30
Q

Give the equation and observation of the substitution reaction that occurs when Concentrated HCL is added to aqueous Cu2+

A

[Cu(H2O)6]2+ (aq) + 4Cl- [CuCl4]2- (aq) + 6H2O (l) Colour change from Blue to Yellow

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31
Q

Give the equation and observation of the substitution reaction that occurs when aqueous ammonia is added to aqueous Cu2+

A

1) when a low conc. of ammonia is added:
a) NH3 + H2O (l) -> (NH4)+ + (OH)- (aq)
b) (Cu)2+ + 2(OH)- -> Cu(OH)2 (s) observation: Blue ppt
2) High concentration NH3:
a) [Cu(H2O)6]2+ + 4NH3 -> [Cu(NH3)4(H2O)2]2+ + 4H2O
observation: blue solution to deep blue solution

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32
Q

Give the equation and observation of the substitution reaction that occurs when concentrated HCl is added to aqueous Co2+

A

[Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2O

Pink solution turns blue

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33
Q

In Haemoglobin, what is the dentate of the Haem group ligand to the (Fe)2+ ion

A

Tetradentate (4)

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34
Q

What is the co-ordination number of Haemoglobin, and state the types of lone pairs in a haemoglobin molecule

A

1) 6 - octahedral
2) tetradentate haem group, protein, water

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35
Q

Give the ligand substitution of haemoglobin

A

let Hb = haemoglobin

Hb-H2O + O2 -> Hb-O2 + H2O

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36
Q

Describe the process of the substitution reaction of haemoglobin in the body

A
  • process allows Hb to transport O2 round the body
    1) Forward reaction occurs in the lungs - High O2 concentration
    2) In low O2 conc. (tissues) , backward reaction occurs - O2 released
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37
Q

Why does CO bind preferentially to oxygen in Hb?

A
  • CO is a better ligand than oxygen - Binding affinity of CO 200X greater than O2
  • > low levels of CO dramatically reduce ability of Hb to carry O2
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38
Q

What are stereoisomers?

A

Same structural formula, different arrangement in space

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39
Q

Which types of ligand complexes does cis-trans isomerism occur in?

A

Square planar and octahedral

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40
Q

What orientation are a pair of ligands in if the bond angle between them is 90*?

A

Cis

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41
Q

What orientation are a pair of ligands in if the bond angle between them is 180*?

A

Trans

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42
Q

What is Cis - platin, and how does it work?

A
  • Pt with 2 Cls and 2 NH3s [Pt(Cl)2(NH3)2]
  • Used in treatment of cancer - stops tumour growth by binding to DNA, stopping cell division
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43
Q

Which ion complexes can exist as optical isomers, and under what circumstances?

A
  • Octahedral - usually 2 or 3 bidentate ligands
  • Tetrahedral - only if 4 different ligands
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44
Q

What does the bond angle in Ammonia change to when it acts as a ligand in a complex, and why does it change?

A
  • 109.5 (from 107)
  • NH3’s lone pair has been converted to a coordinate bond - so no lone pairs in N’s outer shell
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45
Q

What is the stability constant of a complex ion? give the symbol used also

A

equilibrium constant for the formation of the complex ion from its constituent ions. (water is discounted)

Kstab

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46
Q

What is an Acid?

A

A proton donor

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47
Q

What is a base?

A

A proton acceptor?

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48
Q

What name is given to the other part of an acid or base that remains unchanged in a reaction?

A

Spectator Ion

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49
Q

Why is the reaction of a metal element and an acid not an acid-base reaction?

A

H+ IS REDUCED

(no change of oxidation state in acid-base)

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50
Q

What is a strong acid? give an equation to demonstrate this

A

An acid which is totally ionised in aqueous solution

HCl (aq) -> H+ (aq) + Cl- (aq)

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51
Q

What is a strong base?

A

A base which is totally ionised in aqueous solution

NaOH (aq) -> Na+(aq) + OH- (aq)

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52
Q

What is a Weak Acid? give an equation to demonstrate this

A

an acid which is only partially ionised in aqueous solution

CH3COOH (aq) CH3COO- (aq) + H+ (aq)

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53
Q

What is a weak base? give an equation to demonstrate this:

A

A base which is partially ionised in aqueous solution​

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54
Q

Write a Brønstead-Lowry equation for the ionisation of Hydrochloric acid:

A

HCl (aq) + H2O (l) -> H3O+ + Cl-

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55
Q

What is the name of H3O+ (aq)?

A

HYDROXONIUM ION

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56
Q

What are Conjugate Pairs?

A

Acid-base pairs, differing only in the extra H+ possessed by the acid

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57
Q

What correlation is there between the strength of a conjugate acid and the strength of its conjugate base?

A

The stronger the conjugate acid, the weaker the conjugate base

(strong acid = equilibrium position of ionisation far to the right)

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58
Q

If two acids are involved in an acid-base reaction, how are their roles decided?

A

The stronger acid acts as the acid

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59
Q

What is the definition of pH?

A

pH= -Log[H+]

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60
Q

How do you find the concentration of H+, given pH?

A

10(-pH)

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61
Q

How do you calculate pH for a strong acid?

A

Strong acids are COMPLETELY IONISED, so

[Acid] = [H+] pH= -log[acid]

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62
Q

Give the equation for the equilibrium constant for the ionisation of water?

A

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

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63
Q

What is Kw?

A

the IONIC PRODUCT OF WATER

Kw = [H+][OH-] Kw = Kc[H2O]

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64
Q

What is the value of Kw at 25ºc?

A

1x10-14 mol2dm-6 (on data sheet)

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65
Q

How the the ratio of H+ ions to OH- ions compare in a neutral solution?

A

SAME CONC OF H+ AND OH-

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66
Q

How the the ratio of H+ ions to OH- ions compare in an acidic solution?

A

HIGHER [H+] than [OH-]

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67
Q

How the the ratio of H+ ions to OH- ions compare in an alkali solution?

A

HIGHER [OH-] than [H+]

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68
Q

How would you calculate the pH of pure water at rtp?

A

Kw = [H+][OH-],

in pure water [H+] = [OH-]

Kw = [H+]^2

[H+] =√Kw

pH = -log[H+] = 7.00

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69
Q

What formula is used to calculate the pH of strong alkalis?

A

Kw = [OH-][H+]

[H+] =Kw/[OH-]

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70
Q

Why does the concentration of a weak acid not immediately indicate the concentration of H+?

A

Weak acids are NOT FULLY IONISED in aqueous solution

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71
Q

What constant is used to calculate [H+] of a weak acid?

A

the acid DISSOCIATION CONSTANT, Ka

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72
Q

How is Ka defined?

A

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

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73
Q

What are the units of Ka?

A

Moldm-3

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74
Q

What factor has an effect on the value of Ka?

A

TEMPERATURE

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75
Q

What does the value of Ka indicate about an acid?

A

LARGER Ka = STRONGER ACID (Higher H+ conc.)

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76
Q

What is pKa?

A

pKa = -logKa

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77
Q

why is pKa often used instead of Ka?

A

Ka is often a very small number

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78
Q

What effect does the strength of an acid have on pKa?

A

STRONGER ACID = SMALLER pKa

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79
Q

What is the general formula for calculating [H+] of a weak acid solution?

A

[H+] = √(Ka[HA])

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80
Q

What is assumed when calculating the pH of an acid, and in what case is this assumption not true?

A

[H+]=[A-]

-> Only true for PURE ACIDS not true if extra acid or extra A- is added

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81
Q

What colour is MnO4-?

A

Purple

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82
Q

What is the colour of the end point of a potassium dichromate titration?

A

Pink

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83
Q

What is the colour change in iodine titrations?

A

Brown to colourless

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84
Q

What substance is often used to intensify the colour of iodine, and what colour does it turn in the presence of iodine?

A

Starch indicator Black

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85
Q

What are the characteristics of a dynamic equilibrium?

A

1) Rate of forward reaction = rate of backward reaction
2) Closed system - substances are not being added or removed
3) macroscopic properties remain constant

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86
Q

What is meant by Kc?

A

1) EQUILIBRIUM CONSTANT

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87
Q

Under what conditions is the value of Kc constant?

A

given TEMPERATURE

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88
Q

How does the value of Kc correlate with the position of equilibrium? for what conditions is this true?

A

higher Kc = position further to right

similar equilibria - Kc has same unit

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89
Q

What effect does an increase in temperature for an exothermic reaction have on the equilibrium constant, and why?

A

1) decrease in value of Kc
2) Position of equilibrium has shifted in the endothermic direction - left

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90
Q

What effect does an increase in temperature for an endothermic reaction have on the equilibrium constant, and why?

A

1) Kc increases
2) equilibrium shifts to endothermic direction to oppose change - right

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91
Q

What effect does an increase in pressure have on the value of Kc?

A

No effect

only effects position of equilibrium - will cause the equation to no longer equal Kc

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92
Q

How can we tell if a system has not reached equilibrium?

A

CONCENTRATIONS WILL NOT BE CONSISTENT WITH Kc

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93
Q

If the value of a concentration equation is higher than Kc, which way will the reaction move as it approaches equilibrium? why?

A

Backward

if calculated value is higher than Kc, concentration on top line must be too high compared to bottom line

concentration reaction will move backward (left) to increase bottom line concentration, and therefore come into line with Kc

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94
Q

What is the movement of electrons in a redox reaction?

A

electrons are transferred from the REDUCING AGENT to the OXIDISING AGENT

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95
Q

What name is given to the system where electrons flow indirectly from the reducing agent to the oxidising agent, causing an electric current?

A

ELECTROCHEMICAL CELL

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96
Q

Which electrode in a half cell contains the oxidising agent?

A

POSITIVE ELECTRODE

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97
Q

What is the purpose of a Salt Bridge?

A

to complete the circuit by allowing the controlled movement of IONS between the salt bridge (not electrons)

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98
Q

How can you construct a simple salt bridge?

A

A piece of filter paper soaked in saturated potassium nitrate solution

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99
Q

What is the correlation between cell potential and current?

A

Electrons move from a region of NEGATIVE POTENTIAL to an area of POSITIVE POTENTIAL

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100
Q

What is another term for voltage?

A

POTENTIAL DIFFERENCE

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101
Q

What is meant by cell potential?

A

The potential difference measured in a cell - measured in volts - always positive

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102
Q

What is the hydrogen electrode made out of?

A

Platinum - Hydrogen gas is bubbled over it in a H+ solution

103
Q

What is the equation for the reaction at the hydrogen electrode?

A

H+ (aq) + e- > 1/2 H2 (g)

104
Q

What factor effects the direction the hydrogen electrode reaction goes in, and the charge of the hydrogen electrode?

A

How easily the other half cell is oxidised/reduced

105
Q

What are standard conditions for a half cell?

A

1 moldm-3 solution 1 atm pressure 298K/25*c temp

106
Q

What is meant by Standard Electrode Potential?

A

The voltage measured in a cell which that half cell is connected to a standard hydrogen electrode, under standard conditions

107
Q

How does the value of the standard electrode potential of a half cell affect whether it becomes the positive or negative electrode?

A

If E^ø is positive, when connected to a hydrogen electrode it will become the positive electrode

108
Q

How does the reactivity of a metal correlate with the Standard Electrode Potential?

A

More reactive = reduction of ions less favourable = more negative E^ø

109
Q

How would you make a half cell for a gas?

A

Bubble gas over Platinum electrode

and immerse in solution of ions

formed by reduction/oxidation of gas

110
Q

How would you construct a half cell for ions of one element in solution?

A

Use a platinum electrode with BOTH IONS AT THE SAME CONCENTRATION

111
Q

What is meant by Standard Cell Potential (E^ø cell)?

A

the DIFFERENCE between 2 E^ø values - always positive

112
Q

How would you decide which half cell would be a negative electrode?

A

More negative E^ø = oxidation more likely = more negative electrode

113
Q

How could you tell if a reaction is feasible from electrode potentials?

A

If the one with the more negative electrode potential is being reduced, it is not feasible

114
Q

What factors may cause a measured E^ø value to be different form predicted E^ø values?

A

1) non-standard conditions - due to le chateliers principal - position of equilibrium shifts, affecting whether reduction or oxidation is more favourable
2) rates of reaction - high activation energy
- > reaction occurs too slowly to come to equilibrium - changes measured E^ø

115
Q

What is a storage cell?

A

An electrochemical cell with the voltmeter replaced by an electrically powered device (e.g. light bulb)

The free energy created by the cell is used to create a voltage

116
Q

Why may an electrochemical cell with sufficient cell potential not be able to be used in practice,?

A

1) Salt bridge has HIGH RESISTANCE

117
Q

What is an example of a storage cell?

A

NICKEL-CADMIUM BATTERIES

118
Q

Why are nickel-cadmium batteries not widely used anymore?

A

1) HIGHLY TOXIC compounds - difficult to dispose of
2) EXPENSIVE - NON RENEWABLE

119
Q

What type of storage cell are nickel-cadmium batteries?

A

RECHARGEABLE CELLS

120
Q

What factor is necessary for a cell to be rechargable?

A

1) electrodes must remain physically intact as the reaction proceeds
- i.e cant change state -

do not lose physicall integrity

121
Q

How would you recharge a cell?

A

1) connect positive electrode to the positive terminal of a power supply (and negative to negative)
2) Electrons are driven back into the cell

122
Q

What is the difference between storage cells and fuel cells?

A

1) Storage cells are sealed systems - the free energy is stored in the cell
2) Fuel cells are not sealed - chemicals constantly flow into the cell

123
Q

What 2 things do fuel cells generally require?

A

1) FUEL (usually HYDROGEN)
2) OXIDANT (usually OXYGEN from the air)

124
Q

What are the electrodes in a Hydrogen fuel cell made out of?

A

Platinum catalyst coated metal

125
Q

What is the reaction at the negative electrode in a hydrogen fuel cell?

A

1) 1/2 H2 -> H+ + e-

Hydrogen is OXIDISED

126
Q

What is the reaction at the positive electrode of a hydrogen fuel cell?

A

1) 2H+ + 1/2O2 + 2e- -> H2O

127
Q

What is the overall cell reaction for a hydrogen fuel cell?

A

H2 + 1/2 O2 -> H2O

128
Q

What is the reaction for the negative electrode of a hydrogen fuel cell under alkaline conditions?

A

1/2H2 + OH- -> H2O + e-

129
Q

What is the reaction for the positive electrode of a hydrogen fuel cell under alkaline conditions?

A

1/2 O2 + H2O + 2e- -> 2OH-

130
Q

What methods can be used for storing hydrogen in Fuel Cell Vehicles, and what are their limitations?

A

1) High pressure - risk of explosion, specialised tanks needed
2) storage as liquid - low temps required, expensive
3) Adsorption on a solid surface - expensive materials
4) Absorption in a solid metal - (release H2 as pressure eases)
5) Hydrogen rich fuels - H2 released by reforming - releases CO2

131
Q

What are the advantages of FCV’s?

A

1) (hydrogen FCVS) only produce water as waste - less polluting
2) much more efficient than traditional combustion engines - even reforming hydrogen rich fuels will produce less CO2

132
Q

What are the limitations of FCV’s?

A

1) Hydrogen supply - H2 doesn’t occur on earth naturally, must be manufactured - costs energy and often produces CO2
2) Hydrogen storage - Compression and liquefaction have high energy costs and risks of explosion - Absorption and Adsorption systems for H2 have a limited lifetime
3) Fuel cells - need regular replacement - expensive to manufacture and involves toxic chemicals

133
Q

What is meant by the Hydrogen Economy?

A

An economy in which our energy needs are met to a substantial extent by hydrogen in the place of fossil fuels

134
Q

What obstacles need to be overcome in order to reach a hydrogen economy?

A

1) Public and political acceptance of hydrogen as a fuel - fear over explosion due to Hindenburg
2) Establishment of infrastructure to ensure hydrogen is widely available - storage and distribution facilities
3) generation of large quantities of hydrogen, which requires energy - will only significantly reduce CO2 emissions is fossil fuels are not used to generate H2 - electrolysis of water using sustainable energy sources

135
Q

What is an Acid?

A

A substance that can donate a H+ ion

136
Q

What is a base?

A

A substance that can accept a H+ ion

137
Q

What name is given to ions in acid-base reactions that are not actively involved in the process?

A

SPECTATOR IONS

138
Q

What is a strong acid?

A

An acid that is TOTALLY IONISED IN AQUEOUS SOLUTION HX -> H+ + X-

139
Q

What is a strong base?

A

A base that is TOTALLY IONISED IN AQUEOUS SOLUTION XOH -> X+ + OH-

140
Q

What is a weak acid?

A

An acid that is only PARTIALLY IONISED IN AQUEOUS SOLUTION HX H+ + X-

141
Q

What is a weak base?

A

A base that only PARTIALLY IONISES IN AQUEOUS SOLUTION XNH2 + H2O XNH3+ + OH-

142
Q

Write the Brønstead-Lowry equation for the ionisation of HCl:

A

HCl (aq) + H2O (aq) Cl- (aq) + H3O+ (aq)

143
Q

What is the name of H3O+?

A

HYDROXONIUM ION

144
Q

What is a Conjugate acid?

A

A Base which has accepted a H+

145
Q

What is a conjugate base?

A

An acid which has donated a H+

146
Q

What name is given to acid-base pairs that only differer by a H+ ion?

A

CONJUGATE PAIRS

147
Q

How does the strength of a conjugate acid affect the strength of a conjugate base?

A

THE STRONGER THE CONJUGATE ACID, THE WEAKER THE CONJUGATE BASE

148
Q

What is rate of reaction?

A

the rate of change of concentration of a reactant or product with time

149
Q

What units are used to measure rate of reaction?

A

Moldm-3s-1

150
Q

How can you measure rate of reaction on a graph plotting concentration against time?

A

Draw a tangent to curve at given time and measure gradient

151
Q

What is meant by the Rate Equation of a reaction?

A

An equation showing how the rate depends on the concentrations of reactants

152
Q

How do you write a rate equation?

A

Rate=K[A]m[B]n

153
Q

How do you calculate the overall order of a reaction?

A

Sum all the separate orders in the rate equation

154
Q

What name is given to the K in a rate equation?

A

Rate Constant

155
Q

What is K a measure of?

A

The probability that a reaction will happen when the particles collide

156
Q

What effect does temperature have on K, and why?

A

Increase in temp = increase in K Due to increase in proportion of reactant molecules or ions with energy greater than the activation energy

157
Q

What effect do other variables - Concentration, pressure, etc. - have on the value of K?

A

NO EFFECT

158
Q

What effect does the addition of a catalyst have on the value of K?

A

May increase K - but often the entire rate equation changes due to a new pathway with lower activation energy

159
Q

What are the units of K?

A

Mol(1-x)dm(3x-3)S-1 Where x is the overall order of reaction

160
Q

What is the half life of a reaction?

A

The time taken for the concentration of a reactant to fall to half of its original value

161
Q

What is the trend in Half Lives for a zero order reaction?

A

SUCCESSIVE HALF LIVES DECREASE

162
Q

What are the units of K for a zero order reaction?

A

Moldm-3s-1 (same as rate)

163
Q

What does a rate v concentration graph look like for a zero order reaction?

A

Horizontal Line

164
Q

What is the trend in half lives for 1st order reactions?

A

SUCCESSIVE HALF LIVES ARE CONSTANT

165
Q

What are the units of K for first order reactions?

A

S-1

166
Q

What does a Rate v concentration graph look like for first order reactions?

A

Positive gradient linear

167
Q

What is the trend of half lives for second order reactions?

A

SUCCESSIVE HALF LIVES INCREASE

168
Q

What are the units of K for second order reactions?

A

Mol-1dm-3s-1

169
Q

What does a rate v concentration graph look like for a second order reaction?

A

Quadratic with positive gradient past origin

170
Q

What are Enthalpy Profile Diagrams?

A

Diagrams which show the difference between the enthalpy of reactants and products

171
Q

What are standard conditions for enthalpy change calculations?

A

100 kPa PRESSURE, SPECIFIC TEMP - 25ºc (unless stated otherwise)

172
Q

What is the standard enthalpy change of a reaction?

A

The enthalpy change when the number of moles of reactants shown in an equation react together under standard conditions

173
Q

What is the standard enthalpy change of formation? (/\Hf)

A

The enthalpy change when one mole of a compound is formed from its elements under standard conditions

174
Q

For what group of compounds is /\Hf always negative?

A

ALL COMMON IONIC COMPOUNDS

175
Q

What is bond enthalpy?

A

The enthalpy change required to BREAK ONE MOLE OF BONDS between TWO ATOMS in a GASEOUS STATE

176
Q

What is the first ionisation energy of an element?

A

The energy needed to REMOVE ONE ELECTRON FROM EVERY ATOM IN EVERY ATOM IN ONE MOLE OF GASEOUS ATOMS in an element

177
Q

What is the second ionisation energy of an element?

A

The energy required to remove ONE ELECTRON IN EVERY ION from ONE MOLE OF GASEOUS 1+ IONS OF AN ELEMENT

178
Q

Why are all ionisations Endothermic? (+/\H)

A

Energy is needed to OVERCOME THE ATTRACTION BETWEEN OUTER ELECTRONS AND NUCLEUS

179
Q

Why are second ionisation energies more Endothermic (more +ve) than first ionisation energies?

A

1) Same no of protons as 1st I.E., but 1 LESS ELECTRON
2) LESS REPULSION between remaining electrons
3) STRONGER ATTRACTION TO NUCLEUS

180
Q

What is Hess’ Law?

A

The enthalpy change in a chemical reaction is INDEPENDENT OF THE ROUTE taken by the reaction, provided the initial and final conditions are the same

181
Q

What is the standard enthalpy change of atomisation?

A

The enthalpy change when ONE MOLE of gaseous atoms of an element are formed, FROM THE ELEMENT IN ITS STANDARD STATE

182
Q

How does the trend in /\Hatomisation change as you go along a period, and why?

A

INCREASES ACROSS A PERIOD No. of outer shell electrons -> MORE ELECTRONS CONTRIBUTING TO METALLIC BONDING

183
Q

When is /\H atomisation not positive?

A

GROUP 8 ELEMENTS - exist as individual atoms

184
Q

What is the first electron affinity of an element?

A

The enthalpy change when ONE ELECTRON is added to EACH ATOM in ONE MOLE OF GASEOUS ATOMS OF AN ELEMENT

185
Q

What is the second electron affinity?

A

The enthalpy change when ONE ELECTRON is added to EACH ION IN A MOLE OF GASEOUS 1- IONS of an element

186
Q

Why are all first electron affinities of elements that commonly form 1- ions negative?

A

The added electron is MORE STRONGLY ATTRACTED TO THE NUCLEUS than it is repelled by other electrons

187
Q

Why are all second electron affinities positive?

A

ENERGY MUST BE PUT IN TO OVERCOME THE REPULSION between the negatively charged X- ion and e- that is added

188
Q

What is lattice enthalpy?

A

the enthalpy change when ONE MOLE of the SOLID COMPOUND is FORMED form its GASEOUS IONS

189
Q

What is lattice enthalpy a measure of?

A

The strength of ionic bonding in a compound

190
Q

Are lattice enthalpies exo or endothermic?

A

Exothermic - when ions form ionic bonds, heat energy is released

191
Q

What is the correlation between lattice enthalpy and strength of ionic bonds?

A

The more exothermic the lattice enthalpy, the STRONGER the ionic bonds

192
Q

What is the main factor that affects lattice enthalpy?

A

CHARGE DENSITY

193
Q

How does charge density affect the attraction of oppositely charged ions?

A

HIGHER CHARGE DENSITY = STRONGER ATTRACTION

194
Q

How does the size of ions affect lattice enthalpy?

A

SMALLER IONIC RADIUS = GREATER CHARGE DENSITY -> STRONGER ATTRACTION between ions = MORE EXOTHERMIC lattice enthalpy

195
Q

How does charge affect lattice enthalpy?

A

GREATER CHARGE = GREATER CHARGE DENSITY -> STRONGER ATTRACTION -> MORE EXOTHERMIC

196
Q

What is the correlation between lattice enthalpies and melting points?

A

HIGHER L.E. = HIGHER MPT as both depend on how much energy is needed to disrupt ionic lattice

197
Q

What is the Enthalpy Change of Solution of an ionic compound?

A

The enthalpy change when 1 MOLE of a COMPOUND DISSOLVES IN WATER

198
Q

What are the 2 steps that form the overall enthalpy change of solution?

A

1) BREAKING OF LATTICE - ENDOTHERMIC - overcoming attraction between oppositely charged ions - = LATTICE ENTHALPY WITH REVERSED CHARGE (+ve)
2) HYDRATION - EXOTHERMIC - ion-dipole forces form - addition of individual ions hydration enthalpies

199
Q

What is meant by Enthalpy Change of Hydration?

A

Enthalpy change when ONE MOLE of gaseous IONS DISSOLVE to form ONE MOLE OF HYDRATED IONS

200
Q

What factor affects the Enthalpy Change of Hydration of an Ion?

A

CHARGE DENSITY GREATER CHARGE DENSITY = STRONGER ION - DIPOLE FORCES = MORE EXOTHERMIC

201
Q

What is entropy?

A

A measure of how disordered the particles in a system are

202
Q

What happens to a system as entropy increases?

A

A SYSTEM BECOMES MORE ENERGETICALLY STABLE AS IT BECOMES MORE DISORDERED (higher entropy = more feasible reaction

203
Q

What are the units for entropy?

A

JK-1Mol-1

204
Q

What happens to the favourability of a system as the value of /\S increases?

A

Higher /\s = MORE FAVOURABLE

205
Q

Why is a solid a low entropy state?

A

Particles are locked together in in a regular LATTICE -> little freedom of movement = HIGHLY ORDERED = LOW ENTROPY

206
Q

Why is a gas a high entropy state?

A

particles free to move = HIGHLY DISORDERED

207
Q

When is the entropy change for the dissolution of a substance negative?

A

for some ions with very high charge density, as water molecules become more ordered

208
Q

what is the formula for calculating /\s?

A

/\s = entropy of products - entropy of reactants (must times by no. of moles of substance in reaction)

209
Q

What factors are favourable for a reaction to occur?

A

1) negative /\H
2) positive /\s

210
Q

what is Free energy?

A

The balance between enthalpy and energy changes, which allow us to predict whether a reaction is feasible or not

211
Q

What symbol is given to free energy change?

A

/\G

212
Q

what is the formula for calculating /\G?

A

/\G = /\H - T/\s

213
Q

how do you calculate T/\s?

A

translate /\s units to kjK-1mol-1

(usually given in JK-1mol-1 - /1000)

convert temp from *c to K (+273) =T

Tx/\s = T/\s

214
Q

In order for a reaction to be energetically feasible, what value must /\G be?

A

/\G<0

215
Q

Why may a reaction still not happen, given that /\G is negative?

A

high activation energy

216
Q

What conditions are necessary for an endothermic reaction to be feasible?

A

ENTROPY INCREASES IN FORWARD REACTION - +/\S

217
Q

What is the definition of pH?

A

-log10[H+]

218
Q

How would you find the pH of a strong acid?

A

[acid] = [H+] pH = log10[H+]

219
Q

What is Kw?

A

The IONIC PRODUCT OF WATER,

Kw = [H+][OH-] ( constant at given temp - value on data sheet)

220
Q

What is the ratio of H+ to OH- in a neutral aqueous solution?

A

Equal concentrations

221
Q

What is the ratio of H+ to OH- in an acid aqueous solution?

A

Higher conc of H+ than OH-

222
Q

What is the ratio of H+ to OH- in an alkali aqueous solution?

A

Higher conc. OH- than H+

223
Q

How would you calculate the pH of a strong alkali solution?

A

[H+] =Kw/[OH-]

224
Q

What do you need to be able to work out the pH of a weak acidic solution?

A

DISSOCIATION CONSTANT (Ka)

225
Q

What is Ka defined as?

A

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

226
Q

What are the units of Ka?

A

Moldm-3

227
Q

What is the relationship between the value of Ka and the strength of an acid?

A

LARGER Ka = higher [H+] = STRONGER ACID

228
Q

What is pKa?

A

-Log10[Ka]

229
Q

What is the correlation between the strength of an acid and the value of pKa?

A

STRONGER ACID = bigger Ka = SMALLER pKa

230
Q

What assumption must be made to calculate the pH of a weak acid?

A

[H+] = [A-], will not apply if extra acid or salt is added

231
Q

What is the formula for calculating the [H+] of a weak acid?

A

[H+] = √(Ka[HA])

232
Q

What is meant by the Equivalence Point of a titration curve?

A

The point at which just enough acid has been added to neutralise the alkali solution the steep, almost vertical point of a pH curve

233
Q

What shape will the acidic portion of a curve have if the acid is strong?

A

exponential curve up to equivalence, vertical part reaches to a quite low pH

234
Q

What shape will the acidic portion of a curve have if the acid is weak?

A

Gradual, almost linear gradient of increase in pH up to equivalence point, reaches vertical point around pH 7

235
Q

What shape will the alkali portion of a pH curve have if the alkali is strong?

A

logarithmic shape to the curve, vertical point finishes around pH 10

236
Q

What shape will the alkali portion of a pH curve have if the alkali is weak?

A

linear curve, starts around pH 8 will level out at a lower pH, but will not fully reach the pH of the pure alkali added

237
Q

How would you choose a suitable indicator for a titration curve?

A

The pH RANGE OF THE INDICATOR SHOULD BE WITHIN THE VERTICAL SECTION OF THE CURVE

238
Q

What would be observed if an unsuitable indicator was chosen, and why?

A

GRADUAL COLOUR CHANGE will not reach/already past EQUIVALENCE POINT - CURVE IS NOT VERTICAL IN INDICATORS pH RANGE

239
Q

What is the standard enthalpy change of neutralisation?

A

THE CHANGE IN ENTHALPY WHEN AN ACID AND BASE UNDERGO A NEUTRALISATION REACTION TO FORM *ONE MOLE OF WATER* UNDER STANDARD CONDITIONS *any ∆H neutralisation reaction equations must be scaled to form one mole of water

240
Q

What equation is used to calculate enthalpy change of neutralisation?

A

mc∆T (Results in J - may need to convert to kJmol-1

241
Q

Why cant mc∆T be used to calculate the enthalpy change of neutralisation of weak acids and bases?

A

The ionisation of the acid/base will also contribute something to the overall enthalpy change

242
Q

What is a buffer solution?

A

A system that MINIMISES pH changes on addition of an acid or base

243
Q

What is an acidic buffer solution formed out of?

A

A WEAK acid and its CONJUGATE BASE

244
Q

What happens if acid is added to an acidic buffer solution?

A

BEFORE EXTRA ACID IS ADDED: XH X- + H+ WHEN ACID IS ADDED: If a small amount of another acid is added to the buffer solution, most of the H+ ions are removed by the reaction with the CONJUGATE BASE X- ( i.e. by the BACK REACTION OF THE DISSOCIATION EQUILIBRIUM) X- + H+ -> HX So [H+] doesnt change much = pH is only slightly changed

245
Q

Describe the action of a buffer solution in terms of Le Chatelier’s Principle?

A

When acid is added to the Buffer, the increase in H+ is opposed by the equilibrium shifting to the left, and forming HX

246
Q

Give the overall equation for the reaction that takes place when more alkali is added to an alkali buffer solution:

A

YOH + OH- YO- + H2O

247
Q

How would you calculate the pH of a buffer based on a weak acid, HA and its salt, A-?

A

[H+] = Ka x ([HA]/[A])

248
Q

Under what conditions is a buffer solution most effective?

A

1) if it contains substantial amounts of acid and conjugate base 2) when pH is close to pKa (if pH = pKa, concs are equal) 3) One pH unit either side of pKa

249
Q

Give an equation for a basic buffer:

A

NH3 + H2O NH4+ + OH-

250
Q

What is the equation for the equilibrium of the dissociation of CO2 in water (e.g. in blood)?

A

H2O + CO2 H2CO3 (carbonic acid)

251
Q

What is the equation for the reaction that forms a buffer solution in blood?

A

H2CO3 H+ HCO3-

252
Q

How is blood CO2 concentration maintained, and how is H2CO3 produced?

A

1) CO2 is produced in respiration and dissolves in blood, forming H2CO3, and is breathed out in the lungs at the same rate

253
Q

How is a roughly constant HCO3- concentration maintained in the body?

A

excess ions are reabsorbed in the kidney

254
Q

Why is maintenance of the bloods pH important?

A

Enzymes that control the bodys biochemistry only work over a narrow pH range

A levels (12 decks)

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