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Chemistry Unit 5 > definitions and model answers > Flashcards

definitions and model answers Flashcards

0
Q

ligand substitution

A

a reaction in which one ligand in a complex ion is replaced by another ligand

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1
Q

How to store hydrogen

A

liquid stored under pressure
adsorbed on the surface of a solid
absorbed within a solid

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2
Q

What is the different between electrochemical and fuel cells?

A

fuel cells convert energy from the reaction of a fuel with oxygen into electrical energy

electrochemical cells generate electrical energy via the electron transfer between half cells of different electrode potential

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3
Q

bidentate ligand

A

ions or molecules, which donate 2 lone pairs or electrons to form 2 coordinate bonds to a central metal ion

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4
Q

redox reaction

A

a reaction in which both reduction and oxidation takes place

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5
Q

coordinate bond

A

a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only

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6
Q

Fuel cell

A

A fuel cell converts the energy from a reaction of a fuel with oxygen into a voltage/electrical energy

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7
Q

precipitation reaction

A

the formation of a solid from a solution during a chemical reaction. precipitates are often formed when two aqueous solutions are mixed together

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8
Q

complex ion

A

a central transition metal ion that is bonded to one or more ligands by coordinate bonds

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10
Q

write an equation for the addition of excess concentrated HCL to a solution of copper sulphate

A

[Cu(H2O)6] 2+ + 4Cl- [CuCl4] 2- + 6H2O

blue solution —-> yellow/green solution

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12
Q

reduction

A

gain of electrons and a decrease in oxidation number

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13
Q

reduction

A

Gain of electrons or a decrease in oxidation number

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14
Q

stability constant kstab

A

the equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution

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15
Q

why are M 3+ hexaaqua ions more acidic than M 2+ hexaaqua ions?

A

the charge density is greater for M 3+ than M 2+

therefore the M 3+ has a greater attraction for H2O ligands

this makes the O-H bonds more polar and weaker

meaning H+ ions are released more easily

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16
Q

write an equation for the reaction of sodium hydroxide with a solution of copper(II) sulphate and give the colour change

A

[Cu(H20)6] 2+ + 2OH- [Cu(H2O)4(OH)2] + 2H2O

blue solution —-> blue precipitate

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17
Q

write an equation for the reaction of sodium hydroxide with a solution of iron (II) sulphate and give the colour change

A

[Fe(H20)6] 2+ + 2OH- [Fe(H2O)4(OH)2] + 2H2O

green solution —-> dirty green precipitate

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18
Q

stereoisomers

A

species with the same structural formula but with a different arrangement of atoms in space

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18
Q

write an equation for the reaction of sodium hydroxide with a solution of iron (III) sulphate and give the colour change

A

[Fe(H20)6] 3+ + 3OH- [Fe(H2O)3(OH)3] + 3H2O

orange yellow solution —-> brown precipitate

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19
Q

write an equation for the addition of excess concentrated HCL to a solution of cobalt chloride

A

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

Pink solution —-> blue solution

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20
Q

Exothermic and the temperature is decreasing…

i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?

A

i) increase
ii) increase
iii) decrease
iv) moves right

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22
Q

write an equation for the addition of excess ammonia to a solution of copper sulphate

A

[Cu(H2O)6] 2+ + 4NH3 [Cu(NH3)4(H2O)2] 2+ + 4H2O

blue solution —-> deep blue solution

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23
Q

How does haemoglobin work

A

in haemoglobin, oxygen bonds to the Fe2+ ion

when required the oxygen is substituted/ released

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24
Q

On a concentration rate graph. what is first order?

A

A straight line with a constant slope
must go through the origin
rate is proportional to concentration
gradient=rate constant (k)

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25
Q

Equilibrium law

A 
For the equilibrium 
aA +bB  cC +dD
Kc = [C]^c [D]^d
        -----------------
         [A]^a [B]^b
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26
Q

oxidation

A

loss of electron and an increase in oxidation number

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27
Q

Rate of reaction

A

The change in the concentration of reactants or products over time

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28
Q

write an equation for the reaction of sodium hydroxide with a solution of cobalt(II) chloride and give the colour changes

A

[Co(H20)6] 2+ + 2OH- [Co(H2O)4(OH)2] + 2H2O

pink solution —–> blue/pink precipitate

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29
Q

Order of reaction

A

The power to which a concentration is raised in the rate equation

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30
Q

Half life

A

The time taken for the concentration of the reactants to drop by half

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31
Q

What are the units of rate?

A

mol dm-3 s-1

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32
Q

units of concentration

A

moldm-3

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33
Q

On a concentration time graph, what is zero order?

A

A straight line with a constant slope

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34
Q

On a concentration time graph, what is first order?

A

Downwardly sloping curve with a constant half life

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35
Q

coordination number

A

the total number of coordinate bonds formed between the central metal ion and any ligand

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36
Q

On a concentration time graph, what is second order?

A

Steeper downwardly sloping curve but levels out quicker

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37
Q

What changes the value of Kc?

A

temperature

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38
Q

ligand

A

atoms, ions or molecules that can donate a lone pair of electrons to form coordinate bonds to a central transition metal ion

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39
Q

the reason CO is a danger to us

A

complexes of haemoglobin and CO have greater Kstab than complexes of haemoglobin and O2. this is because the coordinate bond with CO is stronger than with O2

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40
Q

Dynamic equilibrium

A

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction

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41
Q

d-block element

A

an element where the d sub-shell is the highest energy sub-shell that is occupied

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41
Q

oxidation number

A

loss of electrons or an increase in oxidation number

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44
Q

Homogeneous equilibrium

A

An equilibrium in which all the species making up the reactants and products are in the same physical state

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45
Q

Le Chatliers principle

A

When a system in dynamic equilibrium is subjected to a change, the system readjusts itself to minimise the effect of the change and to restore equilibrium

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46
Q

If Kc=1

A

The position of equilibrium is halfway between the reactants and products

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47
Q

Enthalpy, ∆H

A

The heat content that is stored in a chemical system

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48
Q

On a concentration rate graph, what is second order?

A

An upward sloping curve

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48
Q

Changing the concentration and pressure - what happens to Kc

A

Kc does not change
The system is no longer in equilibrium
State the effect of the change on values in the Kc expression (e.g. the increase in pressure increases the terms on the bottom of the Kc expression more than the terms on top)
State how the terms of the Kc expression alter to oppose the change (e.g. The top of the Kc expression increases and the bottom decreases until Kc is reached/restored)
Equilibrium will shift left/right to restore Kc

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49
Q

Ka

A

for the acid HA
ka = [H+(aq)][A-(aq)]
———————-
[HA(aq)]

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50
Q

If Kc<1

A

The position of equilibrium is on the left hand side (reactants) of the reaction

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51
Q

Rate determining step

A

Defined as the slowest step to a reaction

52
Q

Endothermic and the temperature is decreasing…

i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?

A

i) decrease
ii) decrease
iii) increase
iv) Moves left

53
Q

What is the equation of the rate?

A

rate = k [A][B]^2

54
Q

Heterogeneous equilibrium

A

An equilibrium in which the species making up the reactants and products are in different physical states

55
Q

Describe the change in equilibrium position due to an decrease in pressure

A

Equilibrium moves to the left/right

As there are more gaseous moles

57
Q

Bronsted Lowry acid

A

A species that is a proton donor

58
Q

Bronsted Lowry base

A

A species that is a proton acceptor

59
Q

Alkali

A

A type of base that dissolves in water to form hydroxide OH- (aq) ions

60
Q

Second ionisation energy

A

the energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

61
Q

Strong acid

A

An acid that completely dissociates in solution

62
Q

Monoprotic acid

A

An acid that releases one H+ ion per acid molecule

62
Q

Diprotic acid

A

An acid that releases two H+ ions per acid molecule

63
Q

Weak acid

A

An acid that partially dissociates in solution

64
Q

Exothermic and the temperature is increasing…

i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?

A

i) decrease
ii) decrease
iii) increase
iv) moves left

67
Q

pKa

A

pKa = -log(ka)

68
Q

Standard enthalpy on neutralisation ∆Hneut®

A

The energy change that accompanies the neutralisation of an aqueous acids by an aqueous base to form one mole of H2O (l) under standard conditions

69
Q

pH

A

pH = -log[H+(aq)]

70
Q

Conjugate acid

A

A species formed when proton is added to a base

71
Q

On a concentration rate graph, what is zero order?

A

A straight line horizontal to the x axis

Rate is independent of concentration

71
Q

If Kc>1

A

The position of equilibrium is on the right hand side (products) of the reaction

71
Q

Conjugate base

A

A species formed when a proton is added to an acid

71
Q

Buffer solution

A

A system that minimises pH changes on addition of small amounts of an acid or a base

72
Q

How does a buffer solution work?

A 
The workings of a \_\_\_\_\_\_\_1\_\_\_\_\_\_\_\_ acid buffer can be explained by
\_\_\_\_\_\_1\_\_\_\_\_\_\_  \_\_\_\_\_\_\_2\_\_\_\_\_\_ + H+
Added acid reacts with \_\_\_\_\_\_\_2\_\_\_\_\_\_
Equilibrium shifts to the left
Added alkali/base reacts with H+
Equilibrium shifts to the right
72
Q

What is the equivalence point?

A

When the volume of one solution has reacted exactly with a known volume of another

73
Q

Describe the change in equilibrium position due to an increase in pressure

A

Equilibrium moves to the left/right

As there are fewer gaseous moles

74
Q

Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation

A

Acid and alkali mixed
amounts of acid and alkali stated
Temp taken at start and finish
Energy - q=mc∆T and the meaning of m, c, ∆T
∆H = -energy change
If temp inc, ∆H=-ve , if temp dec, ∆H=+ve

76
Q

First electron affinity

A

The enthalpy change that accompanies the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

79
Q

Standard enthalpy change of reaction ∆Hr®

A

The enthalpy change that accompanies a reaction in the molar quantities expresses in a chemical equation under standard conditions, all reactants and products being in their standard states

80
Q

Lattice enthalpy

A

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

81
Q

Standard enthalpy of atomisation

A

The enthalpy change that takes place when one mole of gaseous atoms form from the element in its standard states

82
Q

transition metal

A

a d-blck element that forms one or more table ions with a partially filled d sub-shell

83
Q

First ionisation energy

A

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

84
Q

Exothermic reaction

A

A reaction in which the enthalpy of products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings. ∆H = -ve

85
Q

A suitable indicator must

A

Change over the vertical section of the curve where there is a large change in pH for the addition of a very small volume

85
Q

Standard enthalpy change of hydration

A

The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions

86
Q

Second electron affinity

A

The enthalpy change that accompanies the addition of one electron to each ion in one mole of gaseous 1- ions to from one mole of gaseous 2- ions

87
Q

Standard enthalpy change of solution

A

The enthalpy change that takes place when one mole of a compound is completely dissolves in water under standard conditions

88
Q

Lattice dissociation enthalpy

A

The enthalpy when one mole of an ionic lattice dissociates into isolated gaseous ions

89
Q

Lattice formation enthalpy

A

The enthalpy change when one mole of an ionic crystal lattice is formed from its isolated gaseous ions

90
Q

Triprotic acid

A

An acid that release three H+ ions per acid molecule

91
Q

Endothermic and the temperature is increasing…

i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?

A

i) increase
ii) increase
iii) decrease
iv) moves right

92
Q

Enthalpy

A

The heat content that is stored in a chemical system

93
Q

Entropy

A

The quantitative measure of the degree of disorder in a system

94
Q

Standard entropy change of reaction ∆S®

A

The entropy change that accompanies a reaction in the molar quantities expresses in a chemical equation under standard conditions, all reactants and products being in their standard states

95
Q

What symbol is associated with entropy?

A

S

96
Q

Standard enthalpy of formation ∆Hf®

A

The enthalpy change that takes place when one mole of a compound in its standard state is formed from its constituents elements in their standard state under standard conditions

97
Q

Units of the free energy calculation

A

∆G = ∆H - T∆S

KJ-1 mol-1 = KJmol-1 - K(JK-1mol-1)

98
Q

When does entropy increase?

A 
Solid melts
Liquid boils
Solid dissolves in water
the number of gas molecules increases
the temperature increases
99
Q

How do you calculate entropy change?

A

∆S = ∑S® products - ∑S® reactants

100
Q

What is the symbol for free energy change

A

∆G

101
Q

If ∆H = -ve
∆S = +ve
i) what will ∆G be?
ii) Will the reaction be feasible?

A

i) always -ve

ii) reaction is feasible

102
Q

If ∆H = +ve
∆S = -ve
i) what will ∆G be?
ii) Will the reaction be feasible?

A

i) Always +ve

ii) reaction is never feasible

103
Q

Ionic product of water, Kw

A

Kw = [H+][OH-] = 1.00 x 10 ^-14 mol2 dm-6 at 25˚C

104
Q

If ∆H = +ve
∆S = +ve
i) what will ∆G be?
ii) Will the reaction be feasible?

A

i) -ve at high temperature

ii) Reaction feasible ay high temperature

105
Q

If ∆G ≤ 0

A

spontaneous reaction

106
Q

Free energy change ∆G

A

The balance between enthalpy, entropy and temperature for a process
∆G = ∆H - T∆S
A process can take place spontaneously when ∆G<0

107
Q

If ∆G ≥0

A

non-spontaneous reaction

108
Q

If ∆G = 0

A

The system is in equilibrium

109
Q

Redox reaction

A

A reaction in which both reduction and oxidation takes place

110
Q

Oxidation number

A

A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules

111
Q

Reducing agent

A

A reagent that reduces (adds electrons to) another species

112
Q

Oxidising agent

A

A reagent that oxidises (takes electrons from) another species

113
Q

Why is platinum electrodes used?

A

The conduct electricity- allows electrons to pass into and out of the cell
They are inert so take no part in the reaction

114
Q

Why might +ve cell potential reactions not happen?

A

The activation energy is too high

There aren’t standard conditions e.g. concentrations are not 1 moldm-3 …

115
Q

Advantages of fuel cells

A

Eliminates pollution causes by burning fossil fuels - the only by product is water

Eliminates greenhouse gases if the hydrogen used comes from electrolysis of water

eliminates economic dependence on politically unstable countries for fossil fuels

Have a higher efficiency than diesel or gas engines

Most operate silently compared to internal combustion engines

Some have low heat transmission - ideal for military applications

operating times are much longer than with batteries

maintenance is simple since there are few moving parts in the system

116
Q

Alternative cells use methanol as the fuel - advantages

A

liquid fuels are easier to store

methanol can be generated from biomass

117
Q

Advantages of fuel cell vehicles

A

produce less pollution from exhaust gases (no NOx, CO, unburnt hydrocarbons)
produce less CO2
more efficient

118
Q

Limited supplies of fossil fuels may causes us to move to a hydrogen economy- however…

A

a greater acceptance by the public and politicians is necessary

handling and maintenance of hydrogen systems must be safe

improvements to hydrogen manufacturing must be made

119
Q

Standard electrode potential

A

The e.m.f. (electromotive force) of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentration of 1 moldm-3 and a gas pressure of 100kPa (1 atmosphere)

121
Q

If ∆H = -ve
∆S = -ve
i) what will ∆G be?
ii) Will the reaction be feasible?

A

i) -ve at low temperatures

ii) Reaction feasible at low temperatures

121
Q

Disadvantages of fuel cells

A

production, transportation, distribution and storage of hydrogen is difficult

reforming is technically challenging and not environmentally friendly

refuelling and starting times of fuel cell vehicles (FCV’s) are longer

driving range cars is shorter than in a tradition vehicle

fuel cells are generally slightly bigger than comparable batteries or engines

currently expensive to produce, since most units are hand made

some use expensive materials

the technology is not yet fully developed and few products are available

122
Q

What is entropy usually measured in?

A

joules

123
Q

Endothermic reaction

A

A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants resulting in heat being taken in from the surroundings, ∆H = +ve

123
Q

disadvantages of hydrogen based fuel cells

A

storage of hydrogen - safety considerations

transportation of hydrogen - low density so expensive to deliver

feasibility of liquified hydrogen under pressure - safety considerations

limited life adsorbed/absorber - economic considerations

limited life cycle of cell - economical considerations

high production costs - economic considerations

use toxic chemicals in cell production - environmental considerations

Chemistry Unit 5 (1 decks)

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