Flashcards in Fuels And Heats Of Reaction Deck (73):
What are hydrocarbons?
Compounds consisting of hydrogen and carbon only, bonded together covalently
Give an example of a hydrocarbon
CH4 - Methane
What are the importance of hydrocarbons
Fuels for combustion
Sources of hydrocarbons
Fossil fuels, crude oil, natural gas and coal
Fossil fuels formed?
Remains of dead animals and plants
Crude oil and natural gas formed?
Remains of marine animals and plants
Digestive tracts [cattle] - greenhouse effect
What are aliphatic hydrocarbons?
Straight and branched chains or rings of carbon atoms other than benzene ring
What is a homologous series?
It's a family of organic compounds with the same general formula, similar chemical properties and successive members differing by CH2
General formula for alkanes
CnH2n + 2
What kinda bonds to alkanes have
Single bonds = saturated
Physical properties of alkanes
Non- polar = insoluble in water but soluble in cyclohexane
Low boiling points = van der waal's forces are easy to break
What are isomers?
Compounds that have the same molecular formula but a different structural formula
What kind of bonds to alkenes have?
Double bond = unsaturated
What's the general formula for alkenes?
Physical properties of alkenes
Low boiling point - the longer the chains the stronger the forces - higher boiling point
What kind of bond in alkynes?
Triple bonds = unsaturated
Physical properties of alkynes?
Low or zero polarity
Low boiling points
What is dehydrocyclisation?
Involves converting chains into rings by removing 2H by heating in presence of suitable catalyst
What is catalytic cracking?
Breaking long chains into shorter chains by heating in the absence of oxygen and presence of a catalyst
[some saturated some unsaturated]
The products of catalytic cracking what are they used for?
Unsaturated - used as feedstock for polymer industry
Saturated - high octane, used for making petrol
Advantages of catalytic cracking
Long chain compounds - converted into more useful compounds
Saturated and unsaturated
Purpose of dehydrocyclisation in oil refining?
Increases octane number which reduces tendency of fuel to cause knocking
What is hess's law?
Heat change of a reaction depends on the initial and final states or the reaction and is indecent of the route taken
What is the name of the oil refining process?
Identify the physical property that is the basis for hydrocarbons in oil refining being isolated as naphtha?
What is oil refining?
When compounds in crude oil are separated according to different boiling points
Give a major use for kerosene
Give a make use for residue
Why are isomerisation and catalytic cracking desirable?
Increase octane number which reduces tendency of fuel to cause knocking
Identify a property of a hydrocarbon that results in its presence in a particular fraction in oil refining
Name the fraction in oil refining that is used for jet fuel
What process is used to convert molecules in the fraction to smaller molecules that are in greater demand
What are the two reference hydrocarbons used to assign octane numbers to fuels?
Heptane and 2,2,4 tri-methylpentane
Give two advantages of adding oxygenates?
Increases octane number which reduces knocking
And reduces pollution
Give an example of an oxygenate
Methyl tertiary- butyl ether
Give two properties of hydrogen that makes it a fuel choice?
High octane number
State one disadvantage of hydrogen as a fuel
Give two ways hydrogen gas is produced industrially
Electrolysis of water
Steam reforming of natural gases [ch4]
Name two structural feature of hydrocarbons with high octane numbers
Short chains, branches
What is the octane number?
Measure of the tendency of a fuel to cause knocking
How can members of same homologous group differ in boiling point?
Smaller - fewer electrons and lower mr
Therefore weaker intermolecular forces
Define heat of combustion
Heat change when one mole of a substance is burned completely in excess oxygen
State the octane number of 2,2,4 trimethylpentane
Explain why MTBE is sometimes added to fuel
Increases octane number and reduces pollution
Name the substance previously added to motor fuel and why was it stopped
Tetraethyl lead - toxic [harmful for the environment] and also poisonous to catalytic converters
What lab apparatuses is used to measure heats of combustion?
Explain the term isomerisation
In presence of heat and suitable catalyst where structural formula is changed and hydrocarbons become branched
How do you know one hydrocarbon has a higher octane number than the other?
Shorter chain and more branches = higher
What is the nature of the chemicals that make up the bulk of crude oil?
Describe how crude oil is separated into useful substances in an oil refinery
Hot crude oil enters the base of column and is heated at the bottom
Vapour moves up series of trays
Depending on b.p
High b.p - fractions come off at lower levels
Low b.p - fractions come off at higher levels
Major use for light gasoline and naphtha fractions of crude oil?
Why is catalytic cracking carried out in oil refining?
To give products with higher octane numbers
Compounds Heptane and Methylbenzene are in the same fraction - which one? In oil refining
Name two properties of compounds are responsible for compounds being found in same fraction in oil refining
Sim boiling point
Sim molecular mass
What is auto ignition?
Ignition before spark is produced
Name the three processes that are carried out in an oil refinery to modify the hydrocarbon structure and improve their octane number
What are the six fractions in crude oil?
1. Refinery gas
2.Light gasoline [petrol]
[RED PONIES NEVER KICK GOOD RIDERS]
Give a use of refinery gas
Domestic heating gas
Give a use of light gasoline
Give a use of Naphtha
Give a use of kerosene
Give a use for gas oil
Give a use for residue
Bitumen, lubricating oil
How is hydrogen as a fuel produced and give an equation
Steam reforming of methane
CH4 + H20 = CO + 3H2
Why are mercaptans added to natural gas?
For detection because they are odourless
What are mercaptans
Sulfur compounds added to LPG and Natural has for detection because they are odourless
What instrument is used to measure heat of combustion
Two components liquified as LPG
What is heat of reaction?
It’s the heat change in KJ/mol as a reaction proceeds according to a balanced chemical equation
What is the principal use made of oxygenates such as MTBE in the petrochemicals industry?
Raise octane number which prevents auto-ignition