Developing Fuels - Unit 2 Flashcards
What are the 4 standard conditions?
1) Standard temp = 298 kelvin (25 0c)
2) Standard pressure = 1 atmosphere pressure
3) Standard concentral = 1 mol dm-3
4) All the substances are in their standard states
What are the reasons why the change in enthalpy of combustion is less than expected and how can these be avoided? (3)
1) Incomplete combustion - provide pure source oxygen
2) Loss of energy to surroundings - lid, wind shield, insulation
3) Not at standard conditions
What is the experiment for the combustion of a fuel? (6)
1) Measure mass of spirit burner containing fuel before exp
2) Measure initial temp of water
3) Warm up the water by roughly 10 degrees celsius
4) Record the final temp of the water
5) Record the mass of the spirit burner containing the fuel after the experiment and from this work out how much fuel was used and convert into moles
6) Use the change in temp water and amount of fuel used in moles and SHC of water to work out the enthalpy change of combustion
What is the formula for Methanol?
CH3OH
What is the Specific Heat Capacity?
The amount of energy required to raise the temperature of 1g of a substance by 1 Kelvin
What is the Standard Enthalpy Change of Combustion?
The amount of energy transferred to the surroundings by complete combustion of ONE mole of a fuel under standard conditions in standard states
If the reaction is exothermic what is the enthalpy change?
Negative
If the reaction is endothermic what is the enthalpy change?
Positive
Are combustion reactions exothermic or endothermic?
Exothermic
What is Incomplete combustion? (2)
1) Not all of the reactants are consumed in incomplete combustion
2) Therefore less energy is produced compared with complete combustion.
What is complete combustion?
All the reactants are completely burned therefore a large quantity of energy is produced
What is the Standard enthalpy change of neutralisation?
The energy transferred when ONE mole of H+ ions react with ONE mole of OH- ions to form ONE mole of water under standard conditions
What type of reaction is making bonds?
Exothermic
What type of reaction is breaking bonds?
Endothermic
What is the equation for the reaction for the enthalpy change of neutralisation?
H+(aq) + OH–(aq) → H2O(l)
In the context of a chemical reaction, What does enthalpy change translate to?
Energy change
What is an extrapolation?
Extending the data to take in to account the solution was cooling (losing energy) as it was warming up
What is Hess’ Law?
The Enthalpy change of a process is independent of the pathway taken assuming the initial and end conditions are the same
What is fuel efficiency / economy ?
The relationship between the distance travelled and the amount of fuel consumed
What is exothermic?
A reaction that gives out energy and heats the surroundings
What is endothermic?
A reaction that takes in energy and cools the surroundings
What is meant by the term energy transferred to the surroundings?
This doesn’t just mean the air. The ‘surroundings’ is anything that energy is transferred to. This could be to a test tube, to water, etc
What does the enthalpy change in a reaction give?
The quantity of energy transferred to or from the surroundings when the reaction is carried out in an open container
How would I measure the enthalpy of a substance
1) You can’t.
2) You can however measure the enthalpy when a reaction occurs
In chemistry, what is a system?
The reactants and products of the reaction that we are interested in
What is standard state?
The physical state of substance under standard conditions
What is 0 K?
Absolute 0, the lowest temperature
What is Kelvin (K)?
The unit of absolute temperature
When should Kelvin be used?
In calculations involving temperature
How do you convert temperature from Celsius Kelvin?
Celsius - Kelvin: +273 to Celsius reading Kelvin - Celsius: -273 from Kelvin reading
Why is the enthalpy change of combustion bigger for some fuels over others?
Because burning some fuels involves making and breaking more bonds than when burning others
What is a rule for equations in the context of enthalpy change of combustion?
Must show one mole of the substance being measured reacting
What is the Standard enthalpy change of formation
The energy transferred when ONE mole of a compound is formed from its elements under standard conditions in standard states
What kind of reaction is neutralisation?
Exothermic
Out of -177 and -189 which is less exothermic?
-177 is less exothermic so therefore gives out less energy and heats the surroundings by less
If you measure a temperature change and the temperature increases what type of reaction is it?
Exothermic
If you measure a temperature change and the temperature goes down what type of reaction is it?
Endothermic
Sulfuric acid formula?
H2SO4
Why does carbon form so many compounds?
Because each carbon atom can form 4 covalent bonds
What does homologous series mean?
A group of molecules that share some structural similarity and all the same functional group
What is the shortened structural formula of C2H6?
CH3 CH3
What is the e- configuration of the hybrid orbital of carbon?
SP(3)
What is a key feature of alkenes and what does this mean?
1) Unsaturated - Doesn’t have as much hydrogen - Has c-c double bonds
What is a key feature of Alkanes?
Saturated
What is a key feature of Cycloalkanes?
They have a ring which isn’t flat
What type of reaction is decomposition?
Endothermic or Exothermic
What compounds do Carbon atoms form and why?
1 - Covalet
2 - Because it has 4 outer e- so a charge of 4+ or 4- would be too low or high so can’t form ionic compounds
What are hydrocarbons?
Compounds containing only carbon and hydrogen atoms
What is the formula for cyclohexane and what type of compound is it?
- C6H12 - Cycloalkane
What is a functional group?
Modifiers that are responsible for the characteristic chemical reactions of a molecule
What are compounds with the -OH group named?
Alcohols
What C-C bond is more reactive, double or single?
The double bond
What is the general formula for Alkanes?
Cn H2n+2 Where n = number of Carbon atoms
What are the names and formula of the first 10 Alkanes?
1 - Methane = CH4 6 - Hexane = C6H14
2 - Ethane = C2H6 7 - Heptane = C7H16
3 - Propane = C3H8 8 - Octane = C8H18
4 - Butane = C4H10 9 - Nonane = C9H20
5 - Pentane = C5H12 10 - Decane = C10H22
What are the 3 common alkyl groups and there formula?
1 - Methyl - CH3
2 - Ethyl - CH2CH3
3 - Propyl - CH3(CH2) 2
What is the general formula of cycloalkanes?
CnH2n
What is a rule when adding the number to the alkyl group?
Keep the number as low as possible
What are the properties of alkanes 1-4?
Colourless gases
What are the properties of alkanes 5-16?
Colourless liquids
What are the properties of alkanes 17+
White, waxy solids
Are Alkanes water soluble and why?
1 - No - The water and Alkane form separate layers
2 - Alkanes contains non-polar molecules whereas water contains polar molecules which attract to each other, preventing the alkane molecules mixing with them
What is energy density?
How much energy you get per kg of fuel
What is the bond enthalpy?
The energy needed to break one mole of a bond to give separate atoms all in the gaseous state
What is the relationship between the bond length and the attraction between the atoms?
The shorter the bond length the stronger the attraction between the atoms
What is the relationship between the bond length and the bonds enthalpy?
The shorter the bond length the higher the bond enthalpy
What type of bonds have the highest bond enthalpies?
Double/triple bonds
Why do some reactions need constant heating?
1 - Because they are only slightly exxothermic therefore only release a small amount of energy - not enough to break new bonds
Does bond breaking release or require energy?
Require
Does bond forming release or require energy?
Release
What is the format for explaining why a reaction is endothermic or exothermic? (4)
1 - Mention both bond breaking and bond forming
2 - State bond breaking requires energy
3 - State bond forming releases energy
4 - Compare the size of the energy changes for bond breaking and bond forming.
Why is the bond calculated enthalpy value different from the measured one?
1 - Bond enthalpies are averages - not specific values for a given molecule
2 - Bond enthalpies are quotes at standard conditions
What compounds can bond enthalpies not be used for?
Ionic
What is the equation for working out the enthalpy change of a reaction in relation to bond enthalpies?
Bond enthalpy Reactants - Bond enthalpy Products
What type of bond do small atoms form and why? (2)
1) Strong covalent bonds
2) Because there are less shells so the e- are closer to the nucleus
3) Therefore there is a stronger electrostatic force which requires more energy to overcome
If the bond enthalpy for bond broken is + 99 what is the bond enthalpy for the same bond made?
-99
What ais the key properties that petrol needs?
1 - Contain short and unbranched hydrocarbons as these have a lower Bp making the petrol more volatile
What is a catalyst? (2)
1 - A substance which increases the rate of reaction by providing an alternative reaction pathway with a lower activation enthalpy
2 - Remains chemically unchanged at the end of the reaction
What are the key products of cracking?
1 - Shorter Alkanes 2 - Alkenes
What is Heterogeneous Catalysis?
When reactants and catalyst in different physical states
What is Homogeneous Catalysis?
When reactants and catalyst in the same physical state
What are the four steps of Heterogeneous Catalysis? (4)
1 - Adsorption - stikcing of the reactants onto the catalysts surface
2 - Reactant bonds break
3 - Product bonds formed
4 - Deadsorption -removal of the products from the catalysts surface
What is an electrophile? (2)
1 - Partially positivly charged molecule which is attarcted to a negativly charged region where it accepts a lone pair of e- to form a covalent bond
What is cracking?
Any reaction in which a larger molecule is made into smaller molecules
What is catalysis?
The process of speeding up a chemical reaction using a catalyst
What is a key feature of catalyst and why?
It must have a large SA for contact with reactants
What is a catalyst poison?
A substance that stops a catalyst functioning properly
How do catalyst poisons stop a catalyst from functioning?(3)
1 - The poison molecules are absorbed more strongly to the catalyst surface than the reactant molecules
2 - The catalyst can’t catalyse a reaction with the poison and so becomes inactive
3 - The poison molecules block the active site of the catalyst therefore reactant molecules cannot be catalysed
Example of how you clean/regenerate the surface of a catalyst? (3)
1 - In cracking of long chain hydrocarbons a layer of carbon is produced on the catalyst surface
2 - This reduces the activity of the catalyst as blocks the absorption of reactant molecules
3 - Hot air is blown through the catalyst and the carbon reacts with the oxygen to form carbon dioxide; cleaning the surface
What happens to the boiling point of alkenes and alkanes as the no. carbon atoms increases?
increases with no. carbon atoms
What does a double bond from and what is this?
1 - Pi bond
2 - Two areas of negative charge, one above and one below
what does a single bond form?
Sigma bond
What is the test for unsaturation?
bubble the hydrocarbon gas through bromine Decolourised = unsaturated
What is a carbocation?
An ion with a positively charged carbon atom
What is an addition reaction?
Where two or more molecules react to produce a single larger molecule
What is a nucleophile?
A substance which has the tendency to donate e-
In a laboratory, how can ethene —> ethanol and what type of reaction is this? (3)
1 - Add concentrated sulfuric acid
2 - Diluting with water
3 - Hydration reaction
What is a hydration reaction?
The addition of water to an alkene
What is produced when ethene + hydrogen and what type of reaction is this?
1 - alkane
2 - hydrogenation
What is polymerisation?
Monomers joined together to produce long chained polymers
What is a polymer?
Large molecule based on a repeating unit, a monomer
What is an amorphous polymer, example?
1 Polymer with no pattern
E.g LDPE
What is a crystalline polymer, example?
1 - Polymer with regular structure
2 - HDPE
What is always the intermediate compound in mechanisms?
carbocation
In ploymersiation, what type of bonds are usually between the monomers?
C=C
What is copolymerisation?
When two types of monomers are used in addition polymerisation both monomers become incorperated into the final polymer
What word is used to represent a benzene ring in a compound?
Phenyl
What is a structural isomer and what are the three variations of this?
1 - Same molecular formula different strictural formula:
2 - Position isomer - functional group in different place
3 - Chain isomer - differnt hydrocarbon chain
4 - Functional group isomers - Differnt functional group
What is stereo isomerism and what are the variations?
Same molecular formula and bonds but different ‘spacial’ arrangement of atoms
E or Z
What is a Z isomer and E isomer and what could they also be called?
Z (cis) = When largest groups are on the same side of the C=C
E (trans) = Biggest groups are on opposite sides od the C=C
What causes Geometric isomerism? (2)
1- The c=c bond can’t rotate
2 - Therefore the groups differ on each carbon in the c=c
Why do Z isomers have lower boilng points than E isomers? (3)
1 - Because the chain is more compact and therefore there is less contact between the molecules
2 - This therefore minises the “id-id” effect
3 - Therefore less energy is required to overcome the attraction between the molecules giving it a lower Bpt
What factors reduces the “id-di” effect? (3)
1 - small no e-
2- Lots of branches as push the chains further apart
3 - Z isomer
What volume does a mole of a gas occupy at room temp and pressure and what is this?
1 - 24dm3
2 - The molar volume
What does avogadros constant represent?
The number of molecules in one mole of gas
What effect does the size of the molecule have on the volume a gas occupies?
Has a negligable effect as the molecules in gas are very far apart compared to their size
At equal volume, room temp and pressure how does the no. molecules a gas contains compare?
They contain the same no. molecules
Under what conditions is the molar volume 24dm3?
Room temp 25oc
Room pressure 1 atmosphere
Under what conditions is the molar volume 22.4dm3?
Standard temp - 00c
Standard pressure - 1 atmos
What is an isomer?
Two molecules that have the same molecular formula but differ in the way their atoms are arranged
What affects the number of isomers a hydrocarbon has?
The number of carbon atoms means more isomers
How do you maximise complete combustion in cars? (3)
1 - Suck in more air
2 - Use less fuel and more air
3 - Use a hotter engine
What are the products produced by incomplete combustion?
1 - Carbon monoxide
2 - Carbon particulates
3 - Unburnt hydrocarbons
4 - Water vapour
What is the issue in having a hotter engine? (4)
1 - Results in higher pressure
2 - Therefore N2 + O2 —> NO more likley
3 - This is toxic and a greenhouse gas
4 - NO combined with H2O can produce nitric acid HNO3 which produces acid rain
How is sulfer dioxide SO2 produced and why is it bad and how are its effects mitigated? (4)
1 - In an hot engine S + O2 —> SO2
2 - This is toxic and a greenhouse gas
3 - SO2 then oxidised to SO3
4 - SO3 +H2O –> H2SO4 (strong acid)
4 - We now have low sulfer fuel
What reaction does a catalytic converter catalyse?
NO + CO Pt/Rh—> CO2 + 1/2 N2
What are alternative fuels? (3)
1 - Hydrogen
2 - Biodiesel
3 - Biofuels
What are the issues with Biofuels? (5)
1 - Use of land for fuel not food
2 - Absorbs mositure - can lead to engine corrosion
3 - Lower energy desnity
4 - car engines would need to be modified
5 - not carbon neutral as CO2 is still produced
when producing and transporting the fuel
What are the issues with hydrogen fuel? (5)
1 - Not widely distributed
2 - Poor energy density
3 - Explosive gas
4 - NOx still produced as there’s stil a high temp + press
5 - Can be produced from Electrolysis of H2O which requires electricity - If this energy comes from fossil fuels then it’s bad for environment
How is hydrogen used as a fuel?
2H2 + O2 —> 2H2O
How is Biodiesel/Biofuel used as a fuel?
Ester + methanol –> Biodiesal/ Biofuel (Ethanol)
At what temps do Pl catalyst work?
Pl = 240oc
but if Rh added then 150oc
What is the purpose of catalytic converters?
Using oxygen convert pollutants into gases naturally present in the air
What fuel does catalyctic converters work on and why can another fuel not be used? (2)
1 - Petrol
2 - Diesal has too much O2 so when NOx converted into N, the N would be oxidised again into NOx
How are the main pollutants in the petrol exhauts removed? (3)
Using a catalytic converter:
1) 2CO + O2 —> 2CO2
2) CxHy + O2 —> CO2 + H2O
3) 2NO + CO –> N2 + 2CO2
Why are biodiesals not nessarcerily carbon neutral?
Energy is used to produce and and distribute the ethanol, releasing CO2 if the energy has come from fossil fuels
What are the reaction conditions for alkene + Br2
heat and pressure
What are the conditions for alkene + HBr?
1 - Sodium Bromide
2 - Sulfuric acid
What are the reaction industrial and laboratory conditions for alkene + H2O? (2)
1) laboratory: Conc. sulfuric acid dilited by H2O
Heat and pressure
2) Industrial: H3PO4 (phosphoric acid)
Heat and pressure
3) Hydration
4) Alcohol formed
What are the conditions for polymerisation of alkene? (2)
Ziegler - Natta catalyst
Heat and pressure
What are the reaction conditions for alkene + H2, what does this produce and what is the reaction? (2)
1 - Nickel catalyst
- 150oc
2 - Hydrogenation
3 - Alkane
Why does a higher bond enthalpy give a shorter bond lenght?
Stronger bonds means the atoms are more strongly attracted and are therefore pulled closer together
What are double bonds made up of?
A sigma and pi bond
What should also be balacanced in a balanced equation?
The charges
What are the advanatges of biofuels? (5)
1 - Renewable
2 - Almost carbon neutral - CO2 they produce when burnt is the CO2 the plants used to mkae it absorb
3 - Can be produced from waste
4 - Biodegradable
5 - Oxygenated so more complete combustion
What are the issues with fossil fuels? (3)
1 - produce SO2 - acid rain
2 - produce particulates - damage to lungs
3 - produces CO - poisonous
What are the disadvantages and advanatges of O3 in the troposphere and stratosphere? (2)(2)
Disadvantages - In troposphere:
1 - Toxic
2 - Can lead to photochemical smog - causes
respiratory problems
Advantages - In stratosphere:
1 - Absorbs harmful ultraviolet radiation by:
O3 ——-> O2 + O
2 - UV causes sunburn and skin cancer
What is the effect of NO2 on O3? (1 +equations)(1)
In stratosphere:
1 - Catalyses the breakdown of ozone:
NO2 + hν → NO + O
NO + O3 → NO2 + O2
NO2 + O → NO + O2
O3 + O → 2O2 overall
In troposphere:
1 - NO2 reacts with O3 to form photochemical
smog
How does a catalyst affect the product produced?
Catalysts do not affect yield
