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A Level Chemistry (OCR B Salters) > Developing Fuels > Flashcards

Developing Fuels Flashcards

1
Q

What is the standard ethalpy change of a reaction?

ΔrH

A

The enthalpy change that occurs between the no. moles of reactant specified by the equation under standard conditions with all substances in their standard states.

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2
Q

What is the standard enthalpy change of combustion?

ΔcH

A

The enthalpy change when 1 mole of substance burns completely in oxygen under standard conditions in standard states

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3
Q

What is the standard enthalpy change of formation?

ΔfH

A

The enthalpy change when 1 mole of a substance is formed from its constituent elements in their standard states unde standard conditions

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4
Q

What is the (standard) enthlpy change of neutralisation?

A

The enthalpy change when 1 mole of H+ ions react with 1 mole of OH- ions to form 1 mole H2O under standard conditions and in solutions with a concentration of 1moldm-3

Defined per mole of H2O formed

Standard ionic equation is always the same

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5
Q

What are standard conditions?

A

Pressure: 1 atmoshpere (101kPa/1.01Nm-2)

Temp: 298K

Concs: 1.00moldm-3

State: Whatever state at 298K

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6
Q

Define system

A

The reactantd + products being measured (inside the reaction vessel)

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7
Q

Deine surroundings

A

Everything else that’s not the system - outside the reaction vessel

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8
Q

What is thermochemistry?

A

The study of the energy + heat associated with chemical reactions

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9
Q

What is enthalpy change?

ΔH

A

The energy transfered to/from the surrondings when the reaction is carried out in an open container

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10
Q

Define enxothermic

A

A reaction that gives out energy from the system to the surroundings and heats them

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11
Q

Define endothermic

A

A reaction that takes energy into the system from the surroundings, cooling the surroundings

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12
Q

Why type of process is bond breaking?

Why?

A

Endothermic as it requires energy

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13
Q

What type of process is bond forming?

Why?

A

Exothermic as energy is released

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14
Q

What are the main features of an endothermic reaction?

What does an enthalpy profile for one look like?

A

Bond breaking

ΔH positive

Takes in energy from surroundings

Cools surroundings

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15
Q

What are the main features of an exothermic reaction?

What does an enthalpy profile for one look like?

A

Bond making

ΔH negative

Gives out energy to surroundings

Heats up surroundings

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16
Q

If the energy released by forming bonds is greater than the energy required to break bonds, what type of reaction occurs?

A

An exothermic reaction

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17
Q

If the energy released by forming bonds is less than the energy required to break bonds, what type of reaction occurs?

A

An endothermic reaction

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18
Q

What formula is used to measure enthalpy change?

A

E = mcΔT

E = energy transfered (KJmol-1)

m = mass (g)

c = specific heat capacity (Jg-1K-1)

ΔT = temp. change (K)

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19
Q

What do experiments to measure enthalpy changes ususally involve?

A

Transfering energy to/from water

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20
Q

0.880g C7H16 undergoes complete combustion. The energy released is used to heat 250cm3 water, the temp of which increases by 19º. Calculate ΔcH in kJmol-1. Give to 2 sig figs.

A

Use E=mcΔT to calculate energy transfered to water.
E = 250 x 4.18 x 19 = 19855J

Convert to kJ = 19.855kJ

  • *Calculate moles** of C7H16 burnt using n= m/Mr
    0. 880/100 = 0.0088mol
  • *Scale energy released** during experiment to that released for 1mol burnt
    19. 855/0.0088 = 2256.25kJmol-1

Write down ΔcH with correct sign, sig figs, units etc.
ΔcH = -2260kJmol-1

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21
Q

What general formula can be used to calculate ΔH of a reaction?

A

ΔH = Hproducts - Hreactants

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22
Q

What is the specific heat capacity (c) of water?

A

4.18Jg-1K-1

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23
Q

What is an alkane?

A

A saturated hydrocarbon

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24
Q

What are the 4 main features of alkanes?

A

Have the general formula CnHn+2

Have names ending in -ane

Are saturated - all bonds between Cs single

Are aliphatic - don’t contain benzene rings

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25
Q

How are alkanes named?

A

Name the longest carbon chain

Identify + name any alkyl side chains in alphabetical order

Use di, tri, tetra before the alkyl prefix is the side chains are identical

Show the position of any side chains using the lowest numbers possible

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26
Q

What is crude oil?

A

A mixture of many hundreds of different hydrocarbons

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27
Q

What is fractional distillation used to do?

A

Seperate the different hydrocarbons within crude oil

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28
Q

What is structural formula?

A

A representation of the atoms, bonds, and groups in a molecule

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29
Q

What is skeletal forumla?

A

A representation of a molecule using lines to represent C-C bonds

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30
Q

What is the name of the shortest alkane?

A

Methane

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31
Q

What is the issue with using structural/skeletal formulae to represent molecules?

How is this problem solved?

A

Don’t accurately represent the 3D shapes of molecules

Wedges and dashed/dotted bonds are used

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32
Q

What do dashed/dotted bonds represent in the 3D structure of a molecule?

A

A bond in the direction behind the plane of the paper

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33
Q

What do wedges represent in the 3D structure of a molecule?

A

A bond in the direction in front of the plane of the paper

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34
Q

What does aromatic mean?

A

An organic molecule/hydrocarbon containing 1+ benzene rings

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35
Q

What is a functional group?

A

A modifier responsible for the characteristic chemical reactions/behaviours of molecules that contain it

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36
Q

What is a homologous series?

A

Series of compounds in which all members have the same functional group but have different carbon chain lengths

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37
Q

What is a hydrocarbon?

A

A compound containing only carbon and hydrogen

(May be used to refer to a section of a molecule)

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38
Q

What is a cycloalkane?

A

A saturated hydrocarbon where the carbon atoms are joined in a ring

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39
Q

What are the 5 main features of a cycloalkane?

A

Have the general forumla CnH2n

Have names begining with cyclo-

Have names ending in -ane

Are saturated - all bonds betweens Cs are single

Are aliphatic

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40
Q

What is an alkene?

A

An unsaturated hydrocarbon containing 1+ C=C bonds

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41
Q

What are the 4 main features of alkenes?

A

Have the general forumla CnH2n

Have names ending in -ene

Are unsaturated - Have 1+ double bonds between C atoms in molecule

Are aliphatic - don’t contain benzene rings

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42
Q

How are alkenes named?

A

Have names ending in -ene

The number preceeding the -ene indicates the position of the double bond

If there is more than 1 double bond there will be more than 1 number. Di, tri, tetra will be used before the suffix if this is the case

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43
Q

What are the bond angles around the C=C bond?

Why?

A

All bond angles around C=C bond 120º

Because there are 3 groups of e- around each C atom - 2 single bonds + 1 double bond

These groups repel each other as far as possible

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44
Q

Describe the bonding in an alkene

A

A C=C bond contains a sigma (σ) bond and a pi (π) bond.

A σ bond is an area of increased e- density between the C atoms. Only contains 1 area of negative charge

A π bond consists of 2 areas of negative charge. One of these is above the line of the atoms and the other is below

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45
Q

Where are σ bonds found?

Where are π bonds found?

A

σ bonds found in single bonds

π bonds found in double bonds (along with a σ bond)

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46
Q

What is an electrophile?

A

A positive ion or molecule with a partial positive charge on one of the atoms

This causes it to be attracted to a negatively charged area

It will react by accepting a lone-pair to form a dative covalent bond

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47
Q

What is electrophilic addition?

A

A reaction in which an electrophile joins onto an alkene/molecule with double/triple bond

No atoms are removed from the alkene/molecule it joins on to

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48
Q

When is a covalent bond said to be polarised?

A

If the electrons are unevenly distribute between the atoms

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49
Q

What is a carbocation?

A

A molecule containing a carbon that has a positive charge

It is formed as an intermediate in electrophilic addition

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50
Q

Describe the electrophilic addition reaction between ethene and bromine

A
  • The bromine molecule approaches the alkene + negative electron sink
  • This causes the electrons in the bromine molecule are repelled back along the molecule causing the electron density to become unevenly distributed. It is polarised
  • The bromine atom nearest the alkene becomes slightly +ively charged and acts as an electrophile
  • A pair of e- from the alkene moves towards the Brδ+ and a C-Br bond is formed
  • The carbon species is now a carbocation
  • The other bromine, now negatively charged, bonds with the carbocation
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51
Q

What is the experimental evidence for the mechanism of electrophilic addition?

A

If Cl- ions are present when ethene reacts with bromine, the molecule BrCH2CH2Cl forms as well as the expected BrCH2CH2Br

This is because both Cl- and Br- ions can attack the intermediate carbocation

I.e. when other anions present, next anion will always to remaining side not added to

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52
Q

What is the general rule that determines where the anion will add to the alkene?

A

Anion will always add (first) to the end with the least steric hindrance

i.e. end with least atoms/molecules in the way

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53
Q

What is the product and conditions for when Br2 is used as an electrophile to react with ethene?

A

CH2BrCH2Br 1,2-dibromoethane

Room temp + pressure

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54
Q

What is the product and conditions for when HBr(aq) is used as an electrophile to react with ethene?

A

CH3CH2Br bromoethane

Aqueous solution, room temp + pressure

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55
Q

What is the product and conditions for when H2O is used as an electrophile to react with ethene?

(Hydration)

A

CH3CH2OH ethanol

Phosphoric acid adsorbed onto silica catalyst, 300ºC + 60atm

If conc H2SO4 used then at 1atm + steam used

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56
Q

What is the product and conditions for when H2 is used as an electrophile to react with ethene?

(Hydrogenation)

A

CH3CH3 ethane

If Pt catalyst, room temp + pressure

If Ni catalyst, 150ºC + 5atm

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57
Q

What is a monomer?

A

A molecule which is the starting material for a polymer

Is unsaturated

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58
Q

What is a polymer?

A

A long-chain molecule formed when lots of small, repeating units called monomers join together

They are saturated

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59
Q

What can be used to test for unsaturation?

A

Bromine - is decolorised if unsaturated.

Goes from brown to colourless

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60
Q

How can bromine be used to test for unsaturation?

A

In the presence of unsaturation, changes from orange to colourless

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61
Q

What 2 general types of alkene monomer can addition polymers be made from?

A

One type of alkene monomer
-A-A-A-A-A-A-

More than one type of alkene monomer (used in copolymerisation)
-A-B-A-B-A-B-

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62
Q

Why can alkenes be used in addition polymerisation but alkanes cannot?

A

Alkenes

Because they contain a double bond and alkanes do not

63
Q

What are the products of addition polymerisation?

A

The polymer and no other products

64
Q

How could the bonds in an addition polymer be described?

How are they different to those in the monomer used to make it?

A

Addition polymers are saturated molecules

The monomers used to make them are unsaturated

65
Q

How are addition polymers named?

A

By putting the name of the monomer in brackets and prefixing with ‘poly’

e.g. poly(cholorethene)

HOWEVER the polymer itself is not an alkene

66
Q

What does the repeating unit/monomer in polybutene look like?

A
67
Q

How are the repeating units of polymers conventionally drawn?

A

Only 2 carbons have bonds extending beyond the brackets.

Further carbons ‘branch’ above/below the 2 main ones so there’s never more than 2 ‘main’ carbons in the brackets

e.g. for poly(butene) the carbons are not in a long line of four, instead the other 2 carbons extend above/below the central 2 in the brackets

68
Q

What is copolymerisation?

A

When more than one type of monomer is used during polymerisation

Polymers have the general structure:
-A-B-A-B-A-B-

69
Q

What is the atom economy for addition polymerisation?

A

100%

70
Q

What is an elastomer?

A

A polymer that returns to its original shape after being deformed

Are soft + springy

71
Q

What are the conditions for addition polymerisation?

A

With a Pt catalyst - room temp + pressure

With a Ni catalyst - high temp + pressure
(100-200ºC + 2-10atm)

72
Q

What is a structural isomer?

What are the 3 types of structural isomerism?

A

Molecules with the same molecular formula but which have different structural formulae

3 types: chain isomerism, position isomerism, functional group isomerism

73
Q

What is molecular formula?

A

Shows the numbers of each type of atom in a molecule

e.g. C6H12

Do not indicate functional groups

e.g. the proper molecular formula of ethanol is C2H6O not C2H5OH

74
Q

What is chain isomerism?

A

The different arrangement arrangement of carbon atoms in a chain.

Chain lengths are different/carbons are in different places in the chain because of branching

e.g. butane + methylpropane both have the molecular formula C4H10

75
Q

What is position isomerism?

A

Where the functional group is situated in different places/potitions in the molecule

e.g. propan-1-ol + propan-2-ol both have the molecular formula C<span>3</span>H<span>8</span>O

76
Q

What is functional group isomerism?

A

Compounds have the same molecular formulae but have different functional groups

e.g. propan-1-ol + methoxyethane

77
Q

What is stereoisomerism?

A

Molecules with the same molecular formula but different arrangements of the atoms in space (different 3D structure)

Excludes any different arrangements due to the molecule rotating as a whole or rotating about particular bonds.

Not the same as structural isomerism!

78
Q

What specific type of stereoisomerism do you need to know about for the exam?

A

Geometric isomerism AKA cis-trans/E-Z isomerism

79
Q

What is needed for stereoisomerism to occur?

A

A double bond between 2 carbon atoms

2 different groups on each double-bonded carbon

(e.g. cannot have 2 different groups on only 1 carbon/end)

80
Q

In terms of stereoisomerism, what does cis- mean?

A

Groups on the same side of the double bond

81
Q

In terms of stereoisomerism, what does trans- mean?

A

Groups on opposite sides of the double bond

82
Q

In terms of stereoisomerism, what does E- mean?

A

The highest priority groups are on opposite sides of the double bond

83
Q

In terms of stereoisomerism, what does Z- mean?

A

The highest priority groups are on the same side of the double bond

(think zame zide…)

84
Q

Why are stereoisomers able to exist?

A

Trying to rotate the carbon-carbon double bond would break the pi bond as the p orbitals forming it wouldn’t line up any more.

This requires energy and only happens if the compound is heated strongly. There’s not enough energy at room temp for this to happen

Hence interconversion of the two isomers doesn’t occur

85
Q

What is Hess’ Law?

A

ΔH for any reaction will be the same regardless of any intermediate stages provided the start + end conditions/points are the same

86
Q

What is the general formula for Hess’ Law?

A

ΔH1 = ΔH2 - ΔH3

87
Q

What is ΔfH of an element in its standard state (under standard conditions)?

A

0

Because forming an element from the same element requires 0 energy

So you don’t need to include the value in Hess’ Law calculation

88
Q

Use the following data to calculate a value for the enthalpy change represented by the equation
C2H5OH + 3O2 → 2CO2 + 3H2O

ΔfH C2H5OH = -277
ΔfH CO2 = -394
ΔfH H2O = -286

A

Construct an enthalpy cycle. Make sure the arrows point the correct way to represent the enthapy changes occuring

Choose suitable labels for each arrow e.g. ΔH1 etc.

Calculate ΔH2 = -227kJmol-1

Calculate ΔH3 = 2x-394 + 3x-286 = -1646kJmol-1

Use the general equation for Hess’ Law to find ΔH1 = ΔH3 - ΔH2(**ΔH1 is the unknown)

ΔH1 = -1646 - (-277) = -1369kJmol-1

89
Q

In a question involving Hess’ Law…

if ΔfH data is given, what will be on the bottom of the cycle and which way will the arrows be pointing?

If ΔcH data is given, what will be on the bottom of the cycle and which way will the arrows be pointing?

A

If ΔfH data is given, elements will be on the bottom and arrows will be pointing up

If ΔcH data is given, combustion products will apeear at the bottom and arrows will be pointing down

90
Q

What is energy density?

A

The amount of energy produced per kg of fuel

91
Q

Define bond enthalpy

A

The energy required to break 1mol of a particular bond. Averaged over a range of different gasous compounds containing that bond

(Basically it’s a measure of strength of a covalent bond)

92
Q

Calculate ΔcH for the following equation using the bond enthalpies below
C2H6 + 31/2O2 → 2CO2 +3H2O

C-C = +347kJmol<sup>-1</sup>
C-H = +413kJmol<sup>-1</sup>​
O=O = +498kJmol<sup>-1</sup>​
C=O = +805kJmol<sup>-1</sup>​
O-H = +464kJmol<sup>-1</sup>​
A

Draw diagrams to show the structures of the reactants + products

List the bonds broken:
1x C-C = +347
6x C-H = +2478
3.5x O=O = =+743
Total = +4568 (+ sign because bond breaking)

List the bonds formed:
4x C=O = -3220
6x O-H = -2784
Total = -6004 (- sign because bond making)

Add together the enthalpy changes for bond breaking + making:
ΔH = =4568 + (-6004) = -1436kJmol-1

93
Q

Why are theoretical calulcations for bond enthalpies often diferent to experimental results?

A

Average bond enthalpies from several compounds are used in the caluclation - the actual bond enthalpies in particular molecules will be vary slightly

Bond enthalpy data are for gaseous molecules - some molecules may be in different states (e.g. liquid) at 298K

94
Q

Does a higher bond enthalpy mean a longer or shorter bond?

A

The higher the bond enthalpy, the shorter the bond

95
Q

Do double + triple bonds have higher or lower bond enthalpies than single bonds?

A

Double + triple bonds have higher bond enthalpies than single bonds

96
Q

What is a chemical bond a balance between?

A

Attractive + repulsive forces

97
Q

Why is it difficult to measure bond enthalpies?

What is done to overcome this?

A

Difficule to measure as there is often more than one type of bond in a compound

Hence an average taken across several different compounds

98
Q

Define cracking

A

A reaction that breaks large molecules into smaller ones

99
Q

Why is cracking done after fractional distillation?

A

Crude oil contains too many high bp fractions + not enough low bp fractions to meet demand

‘Straight-run’ gasoline from primary distillation is poor quality + needs refining further

100
Q

What is a catalyst?

A

Substance which speeds up the rate of chemical reaction by providing an alternate reaction pathway with a lower EA

Is not chemically changed/used up at the end of the reaction

(Although may form intermediates or be poisoned)

101
Q

What is catalysis?

A

The acceleration of a chemical reaction by a catalyst

2 types - heterogenous + homogeneous

102
Q

How does a catalyst affect the enthalpy change of a reaction?

A

It doesn’t!

The enthalpy change remains the same

103
Q

What is a homogeneous catalyst?

A

A catalyst which is in the same physical state as the reactants

104
Q

What is a heterogeneous catalyst?

A

A catalyst which is in a different physical state to the reactants

105
Q

What is a catalyst poison?

How do they work?

A

A substance which irriversibly binds to the catalyst surface, blocking its active site and stopping it from functioning properly

Prevents/inhibits other/fewer reactants being adsorbed so the catalyst becomes less efficient

106
Q

What type of catalyst is a catalytic converter in a car an example of?

Why?

A

A heterogeneous catalyst

The reactants are the exhaust fumes whilst the catalyst is a solid (finely-divided) metal (e.g. Pt/Rh)

107
Q

What can reduce the effectiveness of heterogeneous catalysts?

A

Catalyst poisons

108
Q

Give an example of a catalyst poison (related to the DF unit…) and what it affects

A

Lead poisons the metal catalytic converters found in cars (e.g. Pt/Rh)

109
Q

What properties must the surface of a heterogenous catalyst have in order to function/catalyse reactions?

A

Must not have a calatyst poison bound to it

Must have a large surface area in order to adsorb reactants.
Hence they are used in a finely-divided form, often on a porous support material

110
Q

Describe + draw diagrams to show the mechanism of heterogeneous catalysis

A
  1. Reactants come into contact with catalyst surface
  2. Reactants adsorbed onto catalyst surface. This weakens intramolecular bonds
  3. New bonds form, creating the products of the reaction
  4. Products diffuse away from the catalyst surface, leaving it free for new reactants to adsorb to
111
Q

Why are heterogenous catalysts able to provide an alternate reaction pathway with a lower EA?

A

They provide a surface on which a reaction may take place

This lowers the EA needed for a successful collision + means the reactants are more likely to collide (which will result in a successful reaction if they have the EA or above)

112
Q

Give details of an experimental procedure to crack a hydrocarbon vapour over a heated catalyst (in the lab).

A
  1. If using a liquid alkane mixture: Place 2 cm depth of mineral wool into a boiling tube, then use a dropper pipette to add approximately 1 cm3 of liquid alkane mix. Rotate the tube to ensure that the liquid alkane mixture soaks into the mineral wool.
  2. Set up the apparatus as shown in the picture
  3. Use a spatula to place some of the catalyst into the middle of the reaction tube. Keep it separate from the alkane mixture + mineral wool. Make sure there is space above the catalyst for gases to pass freely over it.
  4. Heat the catalyst strongly with a Bunsen flame. Once it’s hot, gently warm the alkane mixture to produce alkane vapour.
  5. Move the Bunsen burner backwards and forwards between the catalyst and the alkane mixture until you have collected several tubes of gas. Stopper the tubes for testing later. The first tube can be discarded because it will contain mainly displaced air from the apparatus
  6. Do not allow water to suck back from the trough
  7. When finished, lift the delivery tube out of the water + leave the apparatus to cool before dismantling it in a fume cupboard
113
Q

Give details of the tests you could perfom (in the lab) on the alkane vapour produced by cracking hydrocarbons in the lab

(i.e. What tests? What do they test for?)

A

Flammability: For solids + liquids, place a spatula end or a few drops of the substance into a combustion spoon* (or dip a glass rod in) and hold in a Bunsen flame.
For gases, use a lit splint to see if the gas is flammable.

Test with bromine water: For solids + liquids, place a spatula end/a few drops of the substance into a test tube. Use pipette approximately 1 cm3 bromine water in, stopper the tube, and shake to mix.
For gases, add approximately 1 cm3 of bromine water directly to the tube, stopper the tube, and shake to mix.

*see photo for picture of combustion spoon

114
Q

How many molecules are in 1mol of gas?

A

6.02x1023

Always equal to Avogadro’s constant

115
Q

What is the molar volume (of gases?)

What does it mean about the relation of the vol of gases to each other?

A

The volume of any gas at RTP will be 24dm3

Means 1mol of any gas occupies same vol so long as conditions the same

RTP = 1atm, 293K

116
Q

What is the ideal gas equation?

A

PV = nRT

P= pressure (Pa)

V = vol (m3)

n = moles

R = gas constant

T = temp (K)

117
Q

What equation can be used to give the number of moles of a gas at RTP?

A

Moles = vol (dm3) / 24.0

So vol = moles x 24.0

118
Q

Convert 1m3 to dm3

Use this to convert 1m3 to cm3

A

1,000dm3

So 1m3 = 1,000,000cm3

(1000dm3 x 1000)

119
Q

What are the 2 general methods that can be used to measure the volume of gases (evolved from a solution)?

A

Using a gas syringe

Using an inverted burette/measuring cylinder

120
Q

What might you take into consideration when deciding whether to use a gas syringe or inverted measuring cylinder/burette to measure the volume of gas evolved from a solution?

What needs to be taken into account regardless (in relation to the gas evolved)?

A

Whether the gas is more/less dense than air - hence whether to use downward/upward delivery

If the gas is soluble in water

Regardless, the reaction may not go to completion, so the vol gas evolved may be lower than expected

121
Q

Why might a gas syringe be used to measure volumes of gases?

A

Up to 100cm3 gas can be colleced

Can be measured to the nearest 1cm3

Can be used if gas soluble in water

Can be used for collection of all gases regardless of density

122
Q

Why might an inverted burette/measuring cylinder be used to measure volumes of gases?

A

Burette can collect up to 50cm3 gas and measure to the nearest 0.1cm3

A measuring cylinder can collect greater volumes (although only measures to nearest 1cm3 like syringe)

Can be used for downward delivery if gas more dense than air

123
Q

Describe how you would set up a reaction to measure the volume of gas evolved from a solution using an inverted measuring cylinder.

A
  1. Place a measuring cylinder filled with water upside down in a water trough so the water doesn’t escape from the measuring cylinder.
  2. Clamp the measuring cylinder in place so that it cannot topple over.
  3. Add a delivery tube to the bottom of the measuring cylinder so gas collected will go into cylinder.
  4. Add reactants to conical flask one after another and place a bung on top of the flask immediately after so no gas can escape.
  5. The volume of gas evolved can be measured by recording the amount by which the water in the cylinder has moved down.
124
Q

Describe how you would set up a reaction to measure the volume of gas evolved from a solution using a gas syringe

A
  1. Attach the gas syringe to a delivery tube. Attach the other end to a bung
  2. Push the plunger in as far as possible (so it’s at 0, or record the starting point)
  3. Mix together the reactants, then quickly replace the bung so no gas escapes
  4. Record the volume of gas evolved once the reaction has gone to completion
125
Q

What is a primary pollutant?

A

A pollutant released directly into the atmosphere

126
Q

What is a secondary pollutant?

A

A pollutant not released directly into the atmosphere

Instead formed from primary pollutants in the atmosphere

127
Q

What goes into a car engine?

What comes out?

A

In: fuel + air

Out: CO2, CO, H2O, SOx, NOx, N2, particulates, unburnt hydrocarbons

128
Q

What is photochemical smog?

A

Smog containing mix of primary + secondary pollutants which absorb light energy and undergo chemical reactions, forming smog

129
Q

What are the effects of photochemical smog?

A
  • Produces ozone + other secondary pollutants/irritating chemicals
  • Ozone is a greenhouse gas + damages lung tissue/immune system
  • Haziness + reduced visibility
  • Eye + nose irritation
  • Difficulty breathing
  • Harmful to plants + animals
  • Damages substances with C=C bond (e.g. plastic + rubber)
130
Q

What are particulates, how are they produced, what effects do they have?

A

Small carbon particles smaller than 2.5x10-12m

Formed from burning fossil fuels + volcanoes

Penetrate the body causing lung cancer + heart attacks
Make surfaces dirty

131
Q

How are unburnt hydrocarbons formed? What effects do they have?

A

Formed from incomplete combusution/leakage from fuel tanks

Can go on to form photochemical smog

132
Q

How is CO produced? What are its effects? How can it be dealt with?

A

Incomplete combustion of hydrocarbons, burning biomass

Is a toxic gas + can form photochemical smog

Catalytic converters oxidise CO to CO2

133
Q

How is CO2 produced? Wha are its effects?

A

Formed from the complete combustion of hydrocarbons

Is a greenhouse gas + causes global warming

134
Q

How are NOx produced? What are their effects? How can they be removed/reduced?

A

Formed from the reaction of oxygen + nitrogen (from the air) at high temps in car engines

NO oxidised to NO2 by O in the air. NO2 linked to respiratory illnesses (e.g. asthma + bronchitis)

NOx dissolve in rain water causing acid rain + can cause photochemical smog

Catalytic converters reduce NO to N2

135
Q

How are SOx formed? What are their effects? How can they be reduced/removed?

A

Formed from the oxidation of sulfur impurities in fuels + volcanoes

Cause acid rain + are toxic gases

Can remove sulfur before burning - desulfurisation

136
Q

Which pollutants harm humans directly?

A

Particulates

CO

NO2

137
Q

Which pollutants harm humans indirectly?

A

Unburnt hydrocarbons

CO2

SOx (acid rain)

NOx (when causing acid rain)

138
Q

What are the effects of acid rain?

A

Breathing difficulties

Kills forests + lake life

Corrodes limestone buildings

139
Q

What are the 3 important reactions that occur in a catalytic converter?

A

Using oxygen to turn CO into CO2

Using oxygen to turn hydrocarbons into CO2 + H2O

Reacting NO with CO to form CO2 + N2

140
Q

How do catalytic converters work/what are their features?

A

Pt/Rh catalyst

Are a fine powder, spread over a ceramic support with many tiny pores forming a honeycomb structure

Need to placed in the correct position so they don’t interfere with stoichiometric air-petrol mixture for optimum fuel consumption

141
Q

What does carbon neutral mean?

A

When burnt release as much CO2 as absorbed when (plant) growing/created

No net increase in production of CO2 - that absorbed balances that produced

A fuel can only be considered this if its production, trasportation, etc. are also carbon neutral

142
Q

What does sustainable mean?

A

Able to be used without having a negative impact on future generations

143
Q

What is a finite resource?

A

A resource that will run out

144
Q

Is diesel a sustainable alternative fuel?

A

No - crude oil is running out

145
Q

What are the benefits/drawbacks of using diesel as an alternative fuel?

A

Less CO2 produced than petrol engine, already sold at petrol stations

Produces more NOx + particulates than petrol engine, not sustainable

146
Q

Is LPG/autogas a suststainable alternative fuel?

A

No - crude oil is running out

147
Q

What are the benefits/drawbacks of using LPG/autogas as an alternative fuel?

A

Less CO, CO2, CxHy, + NOx than petrol engine, petrol engines easily converted to use it

Needs to be stored under pressure so it’s a liquid, not sustainable

148
Q

Is ethanol a sustainable alternative fuel?

A

Possibly not -

Large amounts of energy needed for cultivating sugar cane for fermentation

149
Q

What are the benefits/drawbacks of using ethanol as an alternative fuel?

A

Less CO, SO2, and NOx than car engine, sugar cane absorbs CO2 when grown (could be carbon neutral), high octane number (higher performance fuel)

Highly flammable, engine cannot run on it alone (max 15%), land could be used for farming etc.

150
Q

Is biodiesel a sustainable alternative fuel?

A

Renewable as can be made from waste plant/animal oils + fats

BUT fossil fuels may be used as energy source in production

But potentially, yes!

151
Q

What are the benefits/drawbacks of using biodiesel?

A

Living things have absorbed CO2, biodegradable, less CO, CxHy, SO2, + particulates than disesel engine

Higher NOx emissions than diesel engine, not necessarily sustainable depending on energy source used to produce

152
Q

Is hydrogen a sustainable alternative fuel?

A

Only if the electricity needed for electrolysis of water is from renewable source (e.g. solar cells)

153
Q

What are the benefits/drawbacks of using hydrogen as an alternative fuel?

A

Water is the only product of combustion, may be sustainable

Highly flammable, high-prssure tank needed to store it as a liquid (otherwise cannot be used)

A Level Chemistry (OCR B Salters) (12 decks)

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