Developing Fuels Flashcards
1
Q
What is the enthalpy change for an exothermic reaction
A
Bond making so gives out heat energy and is a negative enthalpy change
2
Q
What is enthalpy change
A
Change in heat energy during chemical reaction from reactants to surroundings
3
Q
Standard enthalpy changes are measured under standard conditions, what are these conditions
A
25 degrees C/298K
1 atmosphere/1.01x10^5 Pa
1 moldm^-3
Chemicals need to be in preferred state at 25 degrees C
4
Q
Standard enthalpy change of combustion
A
When 1 mole of substance is completely burned in oxygen under standard conditions
5
Q
Explain a fuel combustion energy change experiment
A
- Known volume of water in copper calorimeter, record water temperature
- Record spirit burner mass (with fuel in)
- Burn till water 30 degrees C
- Take water temperature (max) reweigh burner
- Calculate energy transferred
6
Q
What is the energy transferred equation
A
Water mass (g) x 4.2 x temperature change(K) M X C x delta T
7
Q
How much is 1 gram in cm^3
A
1 g = 1 cm^3
8
Q
Standard enthalpy change of formation
A
When 1 mole of compound is formed from elements in standard states
9
Q
Why does standard enthalpy formation changes have to be calculated indirectly from enthalpy combustion change
A
Difficult to cause reactants to react under standard conditions so use standard enthalpy combustion change in an enthalpy cycle
10
Q
What does Hess’s law state
A
Chemical reaction is independent of the route taken if initial, final conditions identical
11
Q
Standard enthalpy change of reaction
A
Enthalpy change that occurs when reactants shown in balanced equation react under standard conditions to give standard state products
12
Q
How is standard enthalpy neutralisation measured
A
From energy out when acid reacts with alkali in aqueous solutions
13
Q
What is the neutralisation ionic equation
A
H(^+) (aq) + OH(^-) (aq) -> H20(l)
14
Q
What is the enthalpy reaction change equation
A
All energy absorbed to break bonds - all energy released to make bonds
15
Q
What is average bond enthalpy
A
Energy needed to break a mole of bonds in gas phase, averages over, any different compounds
16
Q
How is bond enthalpy and bond length related
A
Positive nuclei attracted to shared electrons, two positive nuclei repel, as do electrons. Between two nuclei attractive and repulsive forces balance, this is bond length. Stronger attraction between atoms, higher bond enthalpy shorter bond length
17
Q
How do you workout gas volumes from balanced symbol equations
A
- Find moles of one of the molecules mass/Mr
- Use balance equation to work out moles of molecule want to find volume of
- Moles x 24dm^3 (as 1 mole of amy gas)
18
Q
How can you use a gas syringe to measure gas volume
A
- Attach gas syringe to reaction vessel opening
- Show total volume gas made (if more than one gas made won’t show how much of each)
- Reaction end when no change in volume
- Vigorous reactions can blow plunger out, careful
- Calculate number molecules in the volume
19
Q
What has the highest entropy level
A
Highest: Gases Aqueous solution Liquid Solid
20
Q
What’s cracking
A
Larger molecule made into smaller molecules, solves supply and demand
21
Q
What are the products of alkanes being cracked
A
Branched alkanes and branched alkenes
OR
Smaller alkanes and cycloalkanes
22
Q
What are the products is cycloalkanes being cracked
A
Alkenes and branched alkenes
23
Q
What are the products of alkenes being cracked
A
Smaller alkenes
24
Q
What does a catalyst do
A
Speeds up chemical reaction, can be recovered chemically unchanged after reaction
25
What happens in a riser reactor
Hot vaporised hydrocarbons and zeolite catalyst fed in bottom of tube, forced up by steam
26
What is the problem in catalytic cracking
Coke forms on catalyst surface, eventually inactive, needs o be regenerated to overcome problem
27
What happens after the riser reactor
It goes into the separator and the steam carries cracked products away, leaving solid catalyst (goes into regenerator hot air blows off coke) back to base of reactor, repeat cycle
28
Why is no extra heating needed in riser reactor
Energy releases burning coke heats catalyst, energy transferred to feedstock, no extra heating
29
What is catalysis
Process that speeds up chemical reaction using catalyst
30
What is homogeneous catalysis
Reactants and catalyst in same physical state
31
What is a heterogeneous catalyst
Reactant and catalyst different physical states
32
What happens when a solid catalyst is used to increase reaction rate, (reaction occurs on solid surface)
1. Reactants, atoms form binds on catalyst surface, they're absorbed
2. Bonds in reactant weakened
3. Reactant bonds break
4. New bonds form between reactants, held close to surface, for, products
5. Weakens bond to catalyst surface, product released
33
Why can't leaded petrol be used in cars with a catalytic converter
Heterogeneous catalysis, poison molecules absorbed stronger to catalyst surface than reactant molecule. Catalyst can't catalyse a reaction of poison - inactive poison molecules block surface sites
34
What does the feedstock process do
Removes soulful compounds and prevents severe catalyst poisoning
35
What are zeolites
Complex large aluminium, silicon, oxygen lattices carrying negative charges
36
What is isomerisation
A molecule with the exact same atoms in a different arrangement
37
How does reforming occur
Uses platinum catalyst suspended on aluminium oxide with various promoters to make catalyst more efficient. Original ,molecules passed as vapours over solid catalyst at around 500 degrees C
38
What is a structural isomer
Have different structural arrangements of atoms but still same molecular formula
39
Why do atoms with same formula and different structure have different properties
Skeleton and functional group could be the same, only functional group attached to different carbon atom. Different physical properties, chemical properties may be different
40
What is the enthalpy change for an endothermic reaction
Bond breaking reaction that takes in heat energy so has a positive enthalpy change
41
What is photochemical smog made of
Mix of primary and secondary pollutants
42
What/how is ozone made
It is a secondary pollutant, not released into atmosphere directly, formed from chemical reactions occur when sunlight shines on mix of primary pollutants oxygen and water vapour
43
Why is ozone vital in stratosphere
Can cause toxic gas, high human health damage, is irritating, acts as greenhouse gas contributes to global warming
44
What does photochemical smog cause
Haziness, reduced visibility close to ground, eye/nose irritation, breathing difficulty, asthma enhanced
45
What is the complete combustion equation
Hydrocarbon + oxygen -> carbon dioxide + water
46
Why does incomplete combustion occur and what does it produce
If oxygen is limited combustion of hydrocarbons lead to water and either carbon monoxide/carbon (particulates) or both
47
What is the product of burning sulfur compounds in fuels
Sulfur dioxide
| S + O2 -> SO2
48
How can nitrogen oxides form
Some made by burning nitrogen compounds in fuels, in low proportions
Nitrogen and oxygen in air react in high temperature if vechile engine
49
How is sulphuric acid formed
Sulfur dioxide and water react in lower atmosphere form weak sulphuric acid
50
How is strong sulfuric acid (VI) made
Sulfur dioxide oxidised to form sulfuric (VI) acid in stratosphere, reacts with atmosphere water
51
How is nitric acid formed
NO and NO2 react with water and oxygen to form nitric acid
2NO + 1 1/2O2 + H2O -> 2HNO3 nitric acid
NO2 + 1/2 O2 +H2O -> 2HNO3 nitric (V) acid, strong
52
What does acid rain cause
Breathing difficulties, corrodes limestone, kills forest/lake life
53
Why does more diesel have more complete combustion and how does it effect the environment
Higher temperature to run engine
| Less carbon dioxide made but more nitrogen oxide
54
What/why are particulates a problem
Tiny particles of liquid in air
| Settle in lungs decrease lung function
55
What do catalytic converters do
Catalyst reactions change pollutants to carbon dioxide, water, nitrogen occur naturally but under exhaust system conditions, go too slowly to remove pollutant
56
What do catalytic converters contain and what reactions do they speed up
Platinum/rhodium on honeycomb structure. They're three way catalysts as speed up reactions
Carbon + oxygen -> carbon dioxide
Hydrocarbons -> carbon dioxide + water
Carbon monoxide + nitrogen oxide -> nitrogen + carbon dioxide (only for petrol)
57
What has be correct in catalyst system for it to work
Air and petrol mix carefully controlled, exact stoichiometric mix for fuel (ratio of hydrocarbon:oxygen for complete combustion)
58
What happens if there is too much fuel in the catalyst mix
If not enough oxygen for complete combustion, can't remove carbon monoxide and hydrocarbons
59
What temperature does a platinum catalyst start working at
240 degrees C
60
If the platinum catalyst is alloyed with rhodium what is the temperature the catalyst starts working at
150 degrees C
61
What is the main pollutant in Diesel engines
Carbon monoxide, hydrocarbons, particulates and nitrogen oxide compounds
62
How are particulates removed by diesel
Particulate filters contain a variety of material e.g ceramic
63
What is regeneration and when does it occur
Burn off carbon particles
| Increase temperature, decided when by vehicle computer but increases fuel consumption
64
How are nitrogen oxides reduced
By recycling exhaust gases cylinder, lowering temperature
65
What are the biggest sources of air pollutant
Transport, industry and power generation
66
How is sulfur dioxide removed from power stations
Using calcium oxide
67
How are particulates removed from power stations
Using wet scrubbers (catch them in water droplets) from some car exhaust using filters
68
How is carbon monoxide helped to fully combust in car petrol
Oxygenates are added
69
How are emissions reduced
New vehicles not allowed to pollute above certain level
Yearly MOT includes emissions test
1992 compulsory new cars catalytic converter
Government tax pollution e.g raise fuel tax
Developing new fuels, cause less pollution
70
What does fractional distillation do
Separates hydrocarbons in crude oil into useful fractions
71
What are organic compounds sub-divided into
Homologous series
72
What are alkanes
Hydrocarbons
Saturated compound
CnH2n+2
73
What are cycloalkanes
Hydrocarbons
Saturated compounds
CnH2n
74
What are alcohols
Contain oxygen
CnH2n+1+OH
-OH is hydroxyl group (functional group) can attach to carbon atom on chain
75
What are alkenes
Unsaturated hydrocarbons
| CnH2n
76
What is a benzene and what causes it to be stable
Benzene has a ring of delocalised electrons
| Quite stable due to double bond electrons delocalised round carbon ring
77
What are benzene ring structures called
Arenes or aromatic compounds
78
What are ethers
Oxygen atom attached to two aryl or alkyl groups
| General formula R-O-R
79
What are aliphatic compounds
Have carbon chains (not rings) e.g alkanes
80
What are aromatic compounds
Contain delocalised electrons in ring e.g benzene
81
What steps are in nomenclature (naming organic compounds)
1. Count carbon atoms in longest continuous chain
2. Main functional group of molecules gives end of name
3. Number carbons in longest chain with main functional group on lowest possible number. If more than one longest, pick one with most side-chains
4. Write carbon number functional groups on before suffix
5. Side chains/less important functional groups added as prefixes in alphabetical order after number carbon atom each attached to
6. If more than one identical side chain/functional group use di- (2)
82
What occurs in addition polymerisation
Alkenes double bond opens and joins to make longer chains - polymers
83
How are alkenes tested for
Bromine water to test for C=C double bond
1. Shake alkene with orange bromine water, solution quickly decolourises
2. Bromine added across double bond, for dibromoalkane
3. Test for unsaturation
84
What type of reaction is bromine reacting with alkene
Electrophilic addition
85
What happens in the electrophilic addition reaction
1. Double bond in alkene repels electrons in Br2, polarising Br-Br
2. Br-Br bind induced polarisation, Br nearest to alkene slightly positive, other slightly negative
3. Alkenes double bond opens as double bond has plenty of electrons, easily attacked by electrophiles, Br (positive) added to alkene
4. Intermediate very unstable tries to bond, Br (7 in outer shell, only bond with one atom)
5. Br attacks positive carbon
86
What is carbocation
Organic ion with positively charged carbon atom
87
What evidence is there for a electrophilic addition reaction mechanism
Once ethane reacts with bromine, form carbocation so can react with another Br- or Cl-
88
How are bromoalkanes formed
Alkenes undergo hydrogen halide addition
89
How can alcohols be made from alkenes
Hydrating alkenes with use of acid catalyst
1. Cold concentrated acid reacts with alkene in electrophilic addition reaction
2. Add cold water and warm products, hydrolysed, form alcohol, not all acid used up, acts as catalyst
90
How can ethanol be made by steam hydration
1. Ethene can be hydrated by steam at 300 degrees C and 60 atm with phosphoric (V) acid catalyst
2. Reversible reaction low, reaction yield (5%) can recycle unreacted ethene gas, overall yield (95%)
91
What makes alkanes more volatile and what does it change
Lower Mr
| Burn easier as react oxygen, alkane must first be vaporised
92
What is an isomer
Distinct compounds with different physical properties, often different chemical properties too
93
What is a structural isomer
Have same molecular formula, atoms bonded different order. Have structural formulae. Various ways structural isomerism occur
94
What is a chain isomers
Only one alkane corresponding to each of the molecular formula, need more than four or more carbon atoms different arrangements are chain isomers
Molecular formula is same, different structure lead to different properties
95
When does position isomerism occur
When there's an atom/group of atoms substituted in carbon chain/ring, functional groups. Occurs when functional group in different positions in molecules
96
What is functional group isomerism
Same molecular formula and different functional group, as have different functional group, in different homologous series
97
What is E/Z isomerism a type of
Stereoisomerism
98
How would you change an Z molecule into an E vice versa
Spin one end of molecule round in relation to other end of molecule round in relation to other end. Must break li bond in double bond first
99
What would the name of the stereoisomers be if the Hydrogens are across the double bond
E isomer
100
What would the name of the stereoisomers be if the Hydrogens are both above or both below
Z isomer
101
What would the name of the stereoisomers be if there are no hydrogens but e.g two CH3 on opposite sides of the bond
Trans isomer
102
What would the name of the stereoisomers be if there are no hydrogens but e.g two CH3 on the same side of the bond
Cis isomer
103
What causes E/Z isomerism
Restricted rotation around C=C double bond
104
Why are single bonded carbon atoms arranges like a tetrahedron
Molecules take shape allows all electrons pairs to get as far from each other as can
1. Carbon atom makes four single bonds, molecule doesn't lie flat. Atoms form 3D tetrahedral structure
2. Angle between any two covalent bonds (109.5)
3. Show bonds are as far apart as can be using wedges and dotted lines
4. Shape round each carbon atom means sing,e bonded carbon atoms
105
If double bond, atoms bonded to carbon what shape is made
Trigonal planar
106
What is a single bond in organic molecules made of. When are they made
Sigma bonds
Formed when two orbitals overlap in straight line between two atoms
Highest electron density between two positive nuclei
Sigma bonds usually strong
107
What is a double bond made of
Sigma and Pi bond made when two p orbitals overlap sideways
| Pi bond weaker than sigma, double bond less than twice as strong as single bond
108
What happens when an alkene reacts with e.g bromine
Breaks double bonds and Br bonds to it
109
What effects how a hydrocarbon burns in an engine
The higher the octane rating the more smoothly it burns
110
What occurs in preignition and which molecule is more prone to it
Straight chain molecules
Petrol and air mix compressed tend to explode, second explosion a spark passed through double explosion causing knocking in engine
111
How can octane rating be increased
Rearranging straight chain molecules into isomers with branched chains
112
Why is it likely that butane content in petrol is likely to be lowered
Volatile, responsible for evaporative emissions
| Causes ozone formation and photochemical smogs
113
Why is butane in petrol if it has bad environmental effects
Helps petrol perform well in modern engines
| If removed must be replaced
114
What is a renewable fuel
Don't add to greenhouse gases(or other pollution) are carbon neutral
Carbon dioxide still given out in making e.g solar panels
115
What are the objections of using renewable fuels
Not sufficiently reliable
| Need lots of e.g wind turbines and get a fraction of energy supplied by fossil fuels (but won't last forever)
116
What are biofuels made of
Derived from renewable plant and animal matter
117
How is biodiesel made
Chemically reducing fats, oils with alcohol producing fatty acid esters - trans-esterfication
118
How is bioethanol made
Ethanol made by sugar fermentation (from crops e.g maize)
119
How is biogas made
Breakdown of organic waste matter
120
What are the advantages of biodiesel over diesel
Make from waste oil rather than fossil fuel oils
Carbon neutral
Some diesel vehicles can run on pure biodiesel (most are regular mixes)
Biodegradable if spill
Contains barely any sulfur, less oxides of sulfur emission
Less particulates, carbon monoxide, hydrocarbons than petrol and diesel
121
What are the disadvantages of biodiesel
Makes more nitrogen oxides
122
What is a benefit of biofuel use
Biofuels made carbon dioxide when burnt, which plants absorb while grow so carbon neutral
123
What is an advantage of biodiesel/gas
Can make from landfill waste
124
What is a problem of biofuel use
Need to modify engine to be able to use high methanol concentration
125
How can hydrogen gas be used
Burned in modified engine
| Used in fuel cell (convert hydrogen to oxygen to water, chemical process makes electricity) water only waste made
126
How can hydrogen be obtained
From sea water, takes energy to extract it. Method to extract it determines how environmentally friendly fuel is e.g if renewable source wind, hydrogen fuel nearly carbon neutral
Hydrogen like an energy carrier
127
Why is transporting and storing hydrogen difficult
Highly flammable, needs liquefying due to low energy to volume ratio of hydrogen gas
Will need a whole new fuel supply infrastructure e.g pipelines
128
What are the advantages of using hydrogen instead of fossil fuels
Renewable made by water electrolysis
Stored, sent down pipelines in same way methane is
Used in internal engine combustion/fuel cells to make electricity
Makes no carbon dioxide/monoxide or hydrocarbons when burnt
129
What are the disadvantages of using hydrogen instead of fossil fuels
Production from water often uses electricity fro, fossil fuel power stations
Less energy dense than petrol, doesn't release a much energy per gram as petrol
Oxides of nitrogen still made at high temperatures a hydrogen interval combustion engine runs at
130
Why may hydrogen economy be beneficial
Would use hydrogen as storing distributing energy. Systems costed over lifetime use, distributing hydrometer by pipeline maybe be cheaper than transmitting energy
131
What does a fuel cell do in a small car and what is the main product
Generate electricity and convert chemical energy from fuel into electricity in a chemical reaction with oxygen/oxidising agent in electrochemical cell
Main product is water
132
What is the main problem of cars running in hydrogen
Large gas volume required to get mileage equivalent to fuel tank of petrol
Needs storing compactly, could store as liquid in high pressure fuel tank
133
What is liquefied petroleum gas from crude oil distillation also called. How is it stored
Auto gas when used in cars
Under pressure store hydrocarbons as liquids
Petrol vehicles can convert to run on both fuels - need bigger fuel tank
134
What does auto gas work in best
| Why is it better for the environment
High performance engines
Makes 20% less carbon dioxide per mile than petrol as higher carbon to hydrogen ratio
Makes less unguents hydrocarbons, nitrogen oxides than petrol
135
Why is petrol better economically than auto gas
Lower road tax and fuel tax
136
What is the bad thing about auto gas
Not many LPG filling stations
137
What is liquid natural gas mainly from
Oil, natural gas fields
138
What must occur for methane to be liquefied
Pressure and cooled below -160 degrees C
139
What changes in the petrol when it is colder
Petrol difficult to vaporise, harder to start car so use different blend. More volatile components (more small molecule hydrocarbons)
140
When does the fuel and air mix to ignite
Just before the piston at the cylinder top when mix is compressed and heats up
141
What is the ideal gas equation
```
pV=nRT
p pressure (Pa)
V volume (m^3)
n gas amount (moles)
R gas constant (JK^-1mol^-1)
T temperature (K)
```
142
Why is it difficult to have affordable clean energy
Increasing competitions from other countries for available supplies, higher prices
Supplies maybe be disrupted by political issues
143
What is the prefix or suffix for alkanes
-ane
144
What is the prefix or suffix for side-chains in branched alkanes
Alkyl-
| -yl
145
What is the prefix or suffix for alkanes
-ene
146
What is the prefix or suffix for haloalkanes/halogenalkanes
chloro-
bromo-
iodo-
147
What is the prefix or suffix for alcohol
-ol
148
What is the prefix or suffix for cycloalkanes
cyclo-
| -ane
149
What is the prefix or suffix for arenes
-benzene
