Developing Fuels Flashcards
Give the equation to work out the mass of a substance from its moles
Mass = Mr x moles
Give the law for the volume of gas
The volume of 1 mole of a gaseous substance is 24dm³ at room temperature and pressure (25°C and 1 atm)
Define ΔHc
The enthalpy change of combustion is the enthalpy change released when 1 mole of a fuel is burnt completely under STP
Define exothermic
A reaction which gives out heat from the system to the surroundings.
ΔH is negative
Define endothermic
A reaction which takes energy into the system from the surroundings
ΔH is positive
Define ΔHf
The enthalpy change of formation is the enthalpy change when 1 mole of a substance is formed from its constituent elements where both reactants and products are in their standard states
Define ΔHr
The enthalpy change for the other reactions under standard conditions may be given the symbol ΔHr
Describe an experiment to measure the enthalpy change of combustion in a lab
Having a metal calorimeter filled with water and a thermometer, above a spirit burner for the chosen fuel, surrounded by draught shields and with a cover over the calorimeter to reduce heat loss
By measuring the initial and final temperature of the water, the initial mass of water and knowing the SHC for water, you can work out the energy transfered by using
ΔE = m x SHC x ΔT
The enthalpy change can be calculated for the combustion of 1 mole of fuel used if you measured the initial and final mass of fuel
Define entropy and give 3 rules associated with it
Entropy is a measure of the number of ways in which particles can be arranged (the disorder in a system)
1) Gases have greater entropy than liquids; liquids have greater entropy than solids
2) Mixtures (e.g. solutions) have greater entropy than liquids
3) If the number of particles increases during the course of a reaction, then entropy usually increases
State Hess’s law
As long as the starting and finishing points are the same, the enthalpy change for a chemical reaction will always be the same, no matter how you go from start to finish
Give the units for enthalpy change
kJmol⁻¹
Define bond enthalpy
The average energy required to break the bonds in 1 mole of gaseous compounds
Give 2 reasons why the enthaply change of combustion may be slightly different from the quoted values, when worked out from bond enthalpies?
1) A bond enthalpy is the average energy needed to break that particular bond and is not specific to the molecule in an equation
2) Bond enthalpies are for gaseous molecules and this may not be their standard state (298K, 1 atm)
State 3 rules about bond enthalpy, it’s length and its strength
- the greater the bond enthalpy, the stronger the bond
- Short bonds are stronger than long bonds
- C=C is shorter and stronger than C-C
Name the functional group in an alcohol
hydoxyl group (-OH)
Give the 3 rules for naming an alcohol
1) Count the number of carbons in the longest chain
2) Replace the e at the end of the parent alkane with -ol (retain the e for a diol or triol)
3) Locate the position of the OH group with as low a carbon number as possible
Give the products for the complete combustion of an alcohol
Carbon Dioxide & Water
Explain why alcohols combust more completely than the corresponding alkane
Because they require less oxygen since they already contain oxygen
Give another name for alcohols and why they are added to petrol
Oxygenates
They produce less carbon monoxide so are added to petrol to reduce pollution
Name the functional group in an ether
Alkoxy group (-OR)
For an ether, which chain is the prefix?
The shorter chain is the prefix
Define crude oil
A mixture of many different hydrocarbons
Name the process used to separate crude oil into fractions of similar boiling points
Fractional distillation
Define a fraction (for hydrocarbons)
A mixture of compounds with a specific boiling point range
For gasoline, give:
i) Boiling point range (°C)
ii) Number of carbons in hydrocarbon
iii) Use
i) 25 - 75 °C
ii) 5 - 7
iii) Petrol
For kerosene, give:
i) Boiling point range (°C)
ii) Number of carbons in hydrocarbon
iii) Use
i) 190 - 250 °C
ii) 10 - 16
iii) Jet fuel
For gas oil, give:
i) Boiling point range (°C)
ii) Number of carbons in hydrocarbon
iii) Use
i) 250 - 350 °C
ii) 14 - 20
iii) Diesel
Define aliphatic
Carbon atoms forming open chains (no ring structures)
Give the general formula for an alkane
CₓH₂ₓ₊₂
Give the general formula for a cycloalkane
CₓH₂ₓ
Define aromatic
Carbon atoms forming a planar, unsaturated ring (e.g. benzene)
Define saturated
All the bonds between carbon atoms are single bonds
Define unsaturated
The is at least 1 double bond between carbon atoms
Define structural isomerism
Structural isomers have the same molecular formula but different structural formulas
Name and describe the 3 main types of structural isomerism
1) Chain isomerism -different carbon chains
2) Positional isomerism - different positions for functional groups
3) Functional group isomerism - different functional groups (e.g. alcohols and ethers)
Give the conditions required for the isomerisation
Platinum and Al₂O₃ catalysts at 250°C with a zeolite sieve to separate the straight chain from the branched alkanes
Give the conditions required for reforming
Platinum and Al₂O₃ catalysts at 500°C and 20 atm with a zeolite sieve to separate the straight chain alkanes from the ring structure compounds
Why is reforming used on straight chain alkanes?
It changes straight chain alkanes into ring structured compounds (such as aromatic and non-aromatic cyclic compounds)
This is because aromatic compounds have octane high octane numbers (above 100) and non-aromatic cyclic compounds have moderately high octane numbers (about 70)
Define octane number
The tendency for a fuel to auto-ignite
A fuel with an octane number of 80 has the same tendency to auto-ignite as a mixture of 80% 2,2,4-trimethylpentane and 20% heptane
Define auto-ignition and what does it cause in petrol engines?
Auto-ignition is the explosion of a fuel without a spark
Auto-ignition causes:
- knocking
- reduced engine performance (fuel economy)
- engine damage
For fuels, is a high or low octane number desirable?
High
What 2 compounds are used as a comparison for octane numbers?
2,2,4-trimethylpentane (octane number 100)
heptane (octane number 0)
Which has a higher octane number:
i) Short-chain or long-chain compounds?
ii) Straight or branched compounds?
iii) Straight chain or cycloalkanes?
iv) Arenes or cycloalkanes?
v) Oxygenates or non-oxygenated?
i) short-chain
ii) branched
iii) cycloalkanes
iv) arenes
v) oxygenates
Give the systematic name for MTBE
Methyl tert-butyl ether
CH₃-O-C(CH)₃
Define catalyst
A catalyst speeds up the rate of reaction by providing an alternate energy pathway, but is not used up
Define heterogeneous catalyst
Catalysts that are in a different physical state to the reactants
Define homogeneous catalyst
Catalysts that are in the same physical state as the reactants
In a catalystic converter, give the reaction platinum and rhodium are involved in
2NO(g) + 2CO(g) → N₂(g) + 2CO₂(g)
Define catalyst poison
A substance that adsorbs on to the catalyst surface and stops it working
State the catalyst used and give the usual products of cracking
Zeolite as a catalyst
Produces a shorter, branched alkane and an alkene
Give the products of reforming
- Alkanes are converted to cycloalkanes and hydrogen
- Cycloalkanes are then converted to arenes and hydrogen
Give the product of isomerisation
Shorter, branched alkanes
Give the equation for energy density and its units
Energy density (kJkg⁻¹) = ΔHc (kJmol⁻¹) x Moles of fuel in 1kg (molkg⁻¹)
Give the 5 pollutants from the exhaust of a petrol engine
1) Unburnt Hydrocarbons (CₓHᵧ)
2) Carbon Monoxide (CO)
3) Carbon Dioxide (CO₂)
4) Nitrogen Oxides (NOₓ)
5) Sulfur Oxides (SOₓ)
For the unburnt hydrocarbons from petrol engines, give:
i) How it is a pollutant
ii) How it is formed
iii) How it is reduced
i) Evaporative emissions and incomplete combustion
ii) Contributes to formation of photochemical smog, causes respiratory problems
iii) Reduced by catalytic converters and oxygenates (but this means CO₂ is increased)
For the Carbon Monoxide from petrol engines, give:
i) How it is a pollutant
ii) How it is formed
iii) How it is reduced
i) Incomplete combustion of hydrocarbons
ii) Toxic to humans; decreasing the uptake of oxygen into the blood
iii) Reduced by catalytic converters and oxygenated (but this means CO₂ is increased). Also reduced in lean burn engines but this may mean CₓHᵧ is increased
For the Carbon Dioxide from petrol engines, give:
i) How it is a pollutant
ii) How it is formed
iii) How it is reduced
i) Complete combustion of hydrocarbons
ii) Causes greenhouse effect and global warming
iii) Hydrogen is the only petrol alternative which doesn’t produce CO₂
For the Nitrogen Oxides from petrol engines, give:
i) How it is a pollutant
ii) How it is formed
iii) How it is reduced
i) Nitrogen from the air reacts with Oxygen from the air in the high temperatures of the engine
ii) Contributes to formation of photochemical smog, causing respiratory problems. Causes acid rain
iii) Reduced by catalytic converters and oxygenated (but this means CO₂ is increased). Also reduced in lean burn engines but this may mean CₓHᵧ is increased
For the Sulfur Oxides from petrol engines, give:
i) How it is a pollutant
ii) How it is formed
iii) How it is reduced
i) Sulfur in petrol reacts with Oxygen in the air in the heat of the engine
ii) Causes acid rain which erodes limestone buildings and damages forests and lakes
iii) Lower sulfur petrol can be produced by desulfurisation
For diesel as an alternative fuel to petrol, give:
i) Its sustainability
ii) Its benefits
iii) Its risks
i) Non-sustainable, crude oil is running out
ii) Less CO produced than from petrol engine, already sold at petrol stations
iii) Produces more NOₓ and particulates than a petrol engine; particulates can irritate lungs
For LPG or autogas as an alternative fuel to petrol, give:
i) Its sustainability
ii) Its benefits
iii) Its risks
i) Non-sustainable, crude oil is running out
ii) Less CO, CO₂, CₓHᵧ and NOₓ than from a petrol engine, petrol engines easily converted
iii) Needs to be stored under pressure so that it is a liquid
For Ethanol as an alternative fuel to petrol, give:
i) Its sustainability
ii) Its benefits
iii) Its risks
i) Possibly not, large amounts of energy is needed for cultivating sugar cane fermentation
ii) Less CO, SO₂ and NOₓ than from a petrol engine, ethanol has a high octane number, sugar cane absorbs CO₂ in growth
iii) Highly flammable
For Biodiesel as an alternative fuel to petrol, give:
i) Its sustainability
ii) Its benefits
iii) Its risks
i) Can be made from waste plant and animal oils and fats so renewable but fossil fuels may be used as an energy source in production
ii) Living things have absorbed CO₂; it is biodegradable; less CO, CₓHᵧ, SOₓ and particulates than from a diesel engine
iii) NOₓ emissions higher than a diesel engine
For Hydrogen as an alternative fuel to petrol, give:
i) Its sustainability
ii) Its benefits
iii) Its risks
i) Only if the electricity needed for electrolysis of water is from a renewable source such as solar cells
ii) Water is the only product of combustion
iii) Highly flammable; high pressure fuel tank needed to store it as a liquid
Define Zeolites
Silicate minerals which contains small channels can act as sieves, only letting small straight chain isomers through
