Developing Fuels Flashcards
What is the enthalpy change for an exothermic reaction
Bond making so gives out heat energy and is a negative enthalpy change
What is enthalpy change
Change in heat energy during chemical reaction from reactants to surroundings
Standard enthalpy changes are measured under standard conditions, what are these conditions
25 degrees C/298K
1 atmosphere/1.01x10^5 Pa
1 moldm^-3
Chemicals need to be in preferred state at 25 degrees C
Standard enthalpy change of combustion
When 1 mole of substance is completely burned in oxygen under standard conditions
Explain a fuel combustion energy change experiment
- 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
What is the energy transferred equation
Water mass (g) x 4.2 x temperature change(K) M X C x delta T
How much is 1 gram in cm^3
1 g = 1 cm^3
Standard enthalpy change of formation
When 1 mole of compound is formed from elements in standard states
Why does standard enthalpy formation changes have to be calculated indirectly from enthalpy combustion change
Difficult to cause reactants to react under standard conditions so use standard enthalpy combustion change in an enthalpy cycle
What does Hess’s law state
Chemical reaction is independent of the route taken if initial, final conditions identical
Standard enthalpy change of reaction
Enthalpy change that occurs when reactants shown in balanced equation react under standard conditions to give standard state products
How is standard enthalpy neutralisation measured
From energy out when acid reacts with alkali in aqueous solutions
What is the neutralisation ionic equation
H(^+) (aq) + OH(^-) (aq) -> H20(l)
What is the enthalpy reaction change equation
All energy absorbed to break bonds - all energy released to make bonds
What is average bond enthalpy
Energy needed to break a mole of bonds in gas phase, averages over, any different compounds
How is bond enthalpy and bond length related
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
How do you workout gas volumes from balanced symbol equations
- 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)
How can you use a gas syringe to measure gas volume
- 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
What has the highest entropy level
Highest: Gases Aqueous solution Liquid Solid
What’s cracking
Larger molecule made into smaller molecules, solves supply and demand
What are the products of alkanes being cracked
Branched alkanes and branched alkenes
OR
Smaller alkanes and cycloalkanes
What are the products is cycloalkanes being cracked
Alkenes and branched alkenes
What are the products of alkenes being cracked
Smaller alkenes
What does a catalyst do
Speeds up chemical reaction, can be recovered chemically unchanged after reaction
What happens in a riser reactor
Hot vaporised hydrocarbons and zeolite catalyst fed in bottom of tube, forced up by steam
What is the problem in catalytic cracking
Coke forms on catalyst surface, eventually inactive, needs o be regenerated to overcome problem
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
Why is no extra heating needed in riser reactor
Energy releases burning coke heats catalyst, energy transferred to feedstock, no extra heating
What is catalysis
Process that speeds up chemical reaction using catalyst
What is homogeneous catalysis
Reactants and catalyst in same physical state
What is a heterogeneous catalyst
Reactant and catalyst different physical states
What happens when a solid catalyst is used to increase reaction rate, (reaction occurs on solid surface)
- Reactants, atoms form binds on catalyst surface, they’re absorbed
- Bonds in reactant weakened
- Reactant bonds break
- New bonds form between reactants, held close to surface, for, products
- Weakens bond to catalyst surface, product released
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
What does the feedstock process do
Removes soulful compounds and prevents severe catalyst poisoning
What are zeolites
Complex large aluminium, silicon, oxygen lattices carrying negative charges
What is isomerisation
A molecule with the exact same atoms in a different arrangement
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
What is a structural isomer
Have different structural arrangements of atoms but still same molecular formula
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
What is the enthalpy change for an endothermic reaction
Bond breaking reaction that takes in heat energy so has a positive enthalpy change
What is photochemical smog made of
Mix of primary and secondary pollutants
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
Why is ozone vital in stratosphere
Can cause toxic gas, high human health damage, is irritating, acts as greenhouse gas contributes to global warming
What does photochemical smog cause
Haziness, reduced visibility close to ground, eye/nose irritation, breathing difficulty, asthma enhanced
What is the complete combustion equation
Hydrocarbon + oxygen -> carbon dioxide + water
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
What is the product of burning sulfur compounds in fuels
Sulfur dioxide
S + O2 -> SO2
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
How is sulphuric acid formed
Sulfur dioxide and water react in lower atmosphere form weak sulphuric acid
How is strong sulfuric acid (VI) made
Sulfur dioxide oxidised to form sulfuric (VI) acid in stratosphere, reacts with atmosphere water
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
What does acid rain cause
Breathing difficulties, corrodes limestone, kills forest/lake life
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
What/why are particulates a problem
Tiny particles of liquid in air
Settle in lungs decrease lung function
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
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)
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)
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
What temperature does a platinum catalyst start working at
240 degrees C
If the platinum catalyst is alloyed with rhodium what is the temperature the catalyst starts working at
150 degrees C
What is the main pollutant in Diesel engines
Carbon monoxide, hydrocarbons, particulates and nitrogen oxide compounds
How are particulates removed by diesel
Particulate filters contain a variety of material e.g ceramic
What is regeneration and when does it occur
Burn off carbon particles
Increase temperature, decided when by vehicle computer but increases fuel consumption
How are nitrogen oxides reduced
By recycling exhaust gases cylinder, lowering temperature
What are the biggest sources of air pollutant
Transport, industry and power generation
How is sulfur dioxide removed from power stations
Using calcium oxide
How are particulates removed from power stations
Using wet scrubbers (catch them in water droplets) from some car exhaust using filters
How is carbon monoxide helped to fully combust in car petrol
Oxygenates are added
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
What does fractional distillation do
Separates hydrocarbons in crude oil into useful fractions
What are organic compounds sub-divided into
Homologous series
What are alkanes
Hydrocarbons
Saturated compound
CnH2n+2
What are cycloalkanes
Hydrocarbons
Saturated compounds
CnH2n
What are alcohols
Contain oxygen
CnH2n+1+OH
-OH is hydroxyl group (functional group) can attach to carbon atom on chain
What are alkenes
Unsaturated hydrocarbons
CnH2n
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
What are benzene ring structures called
Arenes or aromatic compounds
What are ethers
Oxygen atom attached to two aryl or alkyl groups
General formula R-O-R
What are aliphatic compounds
Have carbon chains (not rings) e.g alkanes
What are aromatic compounds
Contain delocalised electrons in ring e.g benzene
What steps are in nomenclature (naming organic compounds)
- Count carbon atoms in longest continuous chain
- Main functional group of molecules gives end of name
- Number carbons in longest chain with main functional group on lowest possible number. If more than one longest, pick one with most side-chains
- Write carbon number functional groups on before suffix
- Side chains/less important functional groups added as prefixes in alphabetical order after number carbon atom each attached to
- If more than one identical side chain/functional group use di- (2)
What occurs in addition polymerisation
Alkenes double bond opens and joins to make longer chains - polymers
How are alkenes tested for
Bromine water to test for C=C double bond
- Shake alkene with orange bromine water, solution quickly decolourises
- Bromine added across double bond, for dibromoalkane
- Test for unsaturation
What type of reaction is bromine reacting with alkene
Electrophilic addition
What happens in the electrophilic addition reaction
- Double bond in alkene repels electrons in Br2, polarising Br-Br
- Br-Br bind induced polarisation, Br nearest to alkene slightly positive, other slightly negative
- Alkenes double bond opens as double bond has plenty of electrons, easily attacked by electrophiles, Br (positive) added to alkene
- Intermediate very unstable tries to bond, Br (7 in outer shell, only bond with one atom)
- Br attacks positive carbon
What is carbocation
Organic ion with positively charged carbon atom
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-
How are bromoalkanes formed
Alkenes undergo hydrogen halide addition
How can alcohols be made from alkenes
Hydrating alkenes with use of acid catalyst
- Cold concentrated acid reacts with alkene in electrophilic addition reaction
- Add cold water and warm products, hydrolysed, form alcohol, not all acid used up, acts as catalyst
How can ethanol be made by steam hydration
- Ethene can be hydrated by steam at 300 degrees C and 60 atm with phosphoric (V) acid catalyst
- Reversible reaction low, reaction yield (5%) can recycle unreacted ethene gas, overall yield (95%)
What makes alkanes more volatile and what does it change
Lower Mr
Burn easier as react oxygen, alkane must first be vaporised
What is an isomer
Distinct compounds with different physical properties, often different chemical properties too
What is a structural isomer
Have same molecular formula, atoms bonded different order. Have structural formulae. Various ways structural isomerism occur
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
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
What is functional group isomerism
Same molecular formula and different functional group, as have different functional group, in different homologous series
What is E/Z isomerism a type of
Stereoisomerism
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
What would the name of the stereoisomers be if the Hydrogens are across the double bond
E isomer
What would the name of the stereoisomers be if the Hydrogens are both above or both below
Z isomer
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
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
What causes E/Z isomerism
Restricted rotation around C=C double bond
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
- Carbon atom makes four single bonds, molecule doesn’t lie flat. Atoms form 3D tetrahedral structure
- Angle between any two covalent bonds (109.5)
- Show bonds are as far apart as can be using wedges and dotted lines
- Shape round each carbon atom means sing,e bonded carbon atoms
If double bond, atoms bonded to carbon what shape is made
Trigonal planar
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
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
What happens when an alkene reacts with e.g bromine
Breaks double bonds and Br bonds to it
What effects how a hydrocarbon burns in an engine
The higher the octane rating the more smoothly it burns
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
How can octane rating be increased
Rearranging straight chain molecules into isomers with branched chains
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
Why is butane in petrol if it has bad environmental effects
Helps petrol perform well in modern engines
If removed must be replaced
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
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)
What are biofuels made of
Derived from renewable plant and animal matter
How is biodiesel made
Chemically reducing fats, oils with alcohol producing fatty acid esters - trans-esterfication
How is bioethanol made
Ethanol made by sugar fermentation (from crops e.g maize)
How is biogas made
Breakdown of organic waste matter
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
What are the disadvantages of biodiesel
Makes more nitrogen oxides
What is a benefit of biofuel use
Biofuels made carbon dioxide when burnt, which plants absorb while grow so carbon neutral
What is an advantage of biodiesel/gas
Can make from landfill waste
What is a problem of biofuel use
Need to modify engine to be able to use high methanol concentration
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
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
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
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
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
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
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
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
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
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
Why is petrol better economically than auto gas
Lower road tax and fuel tax
What is the bad thing about auto gas
Not many LPG filling stations
What is liquid natural gas mainly from
Oil, natural gas fields
What must occur for methane to be liquefied
Pressure and cooled below -160 degrees C
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)
When does the fuel and air mix to ignite
Just before the piston at the cylinder top when mix is compressed and heats up
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)
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
What is the prefix or suffix for alkanes
-ane
What is the prefix or suffix for side-chains in branched alkanes
Alkyl-
-yl
What is the prefix or suffix for alkanes
-ene
What is the prefix or suffix for haloalkanes/halogenalkanes
chloro-
bromo-
iodo-
What is the prefix or suffix for alcohol
-ol
What is the prefix or suffix for cycloalkanes
cyclo-
-ane
What is the prefix or suffix for arenes
-benzene
