Developing Fuels

Question 1

Give the equation to work out the mass of a substance from its moles

Answer 1

Mass = Mr x moles

Question 2

Give the law for the volume of gas

Answer 2

The volume of 1 mole of a gaseous substance is 24dm³ at room temperature and pressure (25°C and 1 atm)

Question 3

Define ΔHc

Answer 3

The enthalpy change of combustion is the enthalpy change released when 1 mole of a fuel is burnt completely under STP

Question 4

Define exothermic

Answer 4

A reaction which gives out heat from the system to the surroundings.
ΔH is negative

Question 5

Define endothermic

Answer 5

A reaction which takes energy into the system from the surroundings
ΔH is positive

Question 6

Define ΔHf

Answer 6

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

Question 7

Define ΔHr

Answer 7

The enthalpy change for the other reactions under standard conditions may be given the symbol ΔHr

Question 8

Describe an experiment to measure the enthalpy change of combustion in a lab

Answer 8

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

Question 9

Define entropy and give 3 rules associated with it

Answer 9

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

Question 10

State Hess’s law

Answer 10

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

Question 11

Give the units for enthalpy change

Answer 11

kJmol⁻¹

Question 12

Define bond enthalpy

Answer 12

The average energy required to break the bonds in 1 mole of gaseous compounds

Question 13

Give 2 reasons why the enthaply change of combustion may be slightly different from the quoted values, when worked out from bond enthalpies?

Answer 13

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)

Question 14

State 3 rules about bond enthalpy, it’s length and its strength

Answer 14

• 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

Question 15

Name the functional group in an alcohol

Answer 15

hydoxyl group (-OH)

Question 16

Give the 3 rules for naming an alcohol

Answer 16

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

Question 17

Give the products for the complete combustion of an alcohol

Answer 17

Carbon Dioxide & Water

Question 18

Explain why alcohols combust more completely than the corresponding alkane

Answer 18

Because they require less oxygen since they already contain oxygen

Question 19

Give another name for alcohols and why they are added to petrol

Answer 19

Oxygenates

They produce less carbon monoxide so are added to petrol to reduce pollution

Question 20

Name the functional group in an ether

Answer 20

Alkoxy group (-OR)

Question 21

For an ether, which chain is the prefix?

Answer 21

The shorter chain is the prefix

Question 22

Define crude oil

Answer 22

A mixture of many different hydrocarbons

Question 23

Name the process used to separate crude oil into fractions of similar boiling points

Answer 23

Fractional distillation

Question 24

Define a fraction (for hydrocarbons)

Answer 24

A mixture of compounds with a specific boiling point range

Question 25

For gasoline, give: i) Boiling point range (°C) ii) Number of carbons in hydrocarbon iii) Use

Answer 25

i) 25 - 75 °C ii) 5 - 7 iii) Petrol

Question 26

For kerosene, give: i) Boiling point range (°C) ii) Number of carbons in hydrocarbon iii) Use

Answer 26

i) 190 - 250 °C ii) 10 - 16 iii) Jet fuel

Question 27

For gas oil, give: i) Boiling point range (°C) ii) Number of carbons in hydrocarbon iii) Use

Answer 27

i) 250 - 350 °C ii) 14 - 20 iii) Diesel

Question 28

Define aliphatic

Answer 28

Carbon atoms forming open chains (no ring structures)

Question 29

Give the general formula for an alkane

Answer 29

CₓH₂ₓ₊₂

Question 30

Give the general formula for a cycloalkane

Answer 30

CₓH₂ₓ

Question 31

Define aromatic

Answer 31

Carbon atoms forming a planar, unsaturated ring (e.g. benzene)

Question 32

Define saturated

Answer 32

All the bonds between carbon atoms are single bonds

Question 33

Define unsaturated

Answer 33

The is at least 1 double bond between carbon atoms

Question 34

Define structural isomerism

Answer 34

Structural isomers have the same molecular formula but different structural formulas

Question 35

Name and describe the 3 main types of structural isomerism

Answer 35

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)

Question 36

Give the conditions required for the isomerisation

Answer 36

Platinum and Al₂O₃ catalysts at 250°C with a zeolite sieve to separate the straight chain from the branched alkanes

Question 37

Give the conditions required for reforming

Answer 37

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

Question 38

Why is reforming used on straight chain alkanes?

Answer 38

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)

Question 39

Define octane number

Answer 39

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

Question 40

Define auto-ignition and what does it cause in petrol engines?

Answer 40

Auto-ignition is the explosion of a fuel without a spark Auto-ignition causes: - knocking - reduced engine performance (fuel economy) - engine damage

Question 41

For fuels, is a high or low octane number desirable?

Answer 41

High

Question 42

What 2 compounds are used as a comparison for octane numbers?

Answer 42

2,2,4-trimethylpentane (octane number 100) | heptane (octane number 0)

Question 43

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?

Answer 43

i) short-chain ii) branched iii) cycloalkanes iv) arenes v) oxygenates

Question 44

Give the systematic name for MTBE

Answer 44

Methyl tert-butyl ether | CH₃-O-C(CH)₃

Question 45

Define catalyst

Answer 45

A catalyst speeds up the rate of reaction by providing an alternate energy pathway, but is not used up

Question 46

Define heterogeneous catalyst

Answer 46

Catalysts that are in a different physical state to the reactants

Question 47

Define homogeneous catalyst

Answer 47

Catalysts that are in the same physical state as the reactants

Question 48

In a catalystic converter, give the reaction platinum and rhodium are involved in

Answer 48

2NO(g) + 2CO(g) → N₂(g) + 2CO₂(g)

Question 49

Define catalyst poison

Answer 49

A substance that adsorbs on to the catalyst surface and stops it working

Question 50

State the catalyst used and give the usual products of cracking

Answer 50

Zeolite as a catalyst | Produces a shorter, branched alkane and an alkene

Question 51

Give the products of reforming

Answer 51

- Alkanes are converted to cycloalkanes and hydrogen | - Cycloalkanes are then converted to arenes and hydrogen

Question 52

Give the product of isomerisation

Answer 52

Shorter, branched alkanes

Question 53

Give the equation for energy density and its units

Answer 53

Energy density (kJkg⁻¹) = ΔHc (kJmol⁻¹) x Moles of fuel in 1kg (molkg⁻¹)

Question 54

Give the 5 pollutants from the exhaust of a petrol engine

Answer 54

1) Unburnt Hydrocarbons (CₓHᵧ) 2) Carbon Monoxide (CO) 3) Carbon Dioxide (CO₂) 4) Nitrogen Oxides (NOₓ) 5) Sulfur Oxides (SOₓ)

Question 55

For the unburnt hydrocarbons from petrol engines, give: i) How it is a pollutant ii) How it is formed iii) How it is reduced

Answer 55

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)

Question 56

For the Carbon Monoxide from petrol engines, give: i) How it is a pollutant ii) How it is formed iii) How it is reduced

Answer 56

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

Question 57

For the Carbon Dioxide from petrol engines, give: i) How it is a pollutant ii) How it is formed iii) How it is reduced

Answer 57

i) Complete combustion of hydrocarbons ii) Causes greenhouse effect and global warming iii) Hydrogen is the only petrol alternative which doesn't produce CO₂

Question 58

For the Nitrogen Oxides from petrol engines, give: i) How it is a pollutant ii) How it is formed iii) How it is reduced

Answer 58

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

Question 59

For the Sulfur Oxides from petrol engines, give: i) How it is a pollutant ii) How it is formed iii) How it is reduced

Answer 59

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

Question 60

For diesel as an alternative fuel to petrol, give: i) Its sustainability ii) Its benefits iii) Its risks

Answer 60

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

Question 61

For LPG or autogas as an alternative fuel to petrol, give: i) Its sustainability ii) Its benefits iii) Its risks

Answer 61

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

Question 62

For Ethanol as an alternative fuel to petrol, give: i) Its sustainability ii) Its benefits iii) Its risks

Answer 62

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

Question 63

For Biodiesel as an alternative fuel to petrol, give: i) Its sustainability ii) Its benefits iii) Its risks

Answer 63

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

Question 64

For Hydrogen as an alternative fuel to petrol, give: i) Its sustainability ii) Its benefits iii) Its risks

Answer 64

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

Question 65

Define Zeolites

Answer 65

Silicate minerals which contains small channels can act as sieves, only letting small straight chain isomers through