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fuels and earth science Flashcards

fuels

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1
Q

what are hydrocarbons

A

compounds that contain carbon and hydrogen only

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2
Q

describe crude oil

A
  • complex mixture of hydrocarbons
  • contains molecules where carbon atoms are in chains or rings
  • and important source of useful substances (fuels and feedstock for petrochemical industry)
  • a finite resource
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3
Q

describe and explain the separation of crude oil into simpler more useful mixtures by the process of fractional distillation

A
  • crude oil separated into fractions - simpler, more useful mixtures containing groups of hydrocarbons of similar lengths
    1. fractions of crude oil separated by fractional distillation
    2. oil heated until most is gas
    3. gas enter fractioning column (liquid bitumen is drained off at bottom)
    4. column has temperature gradient (i e cooler as you go up hot at bottom)
    5. longer hydrocarbons = higher boiling points, turn into liquids and drain out of column early on when near bottom
    6. shorter hydrocarbons = lower boiling points, turn into liquid and drain out later on near top where cool
    7. crude oil ends up separated into different fractions, each with a mixture of hydrocarbons (mostly alkenes) with similar boiling points
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4
Q

what is the fraction gas used for

A
  • domestic heating and cooking
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5
Q

what is the fraction kerosene used for

A

-fuel in aircraft

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6
Q

what is the fraction petrol used for

A
  • fuel in cars
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7
Q

what is the fraction diesel oil used for

A
  • fuel for some cars and trains
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8
Q

what is the fraction fuel oil used for

A
  • fuel for large ships
    -power stations
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9
Q

what is the fraction bitumen used for

A
  • surface roads and roofs
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10
Q

explain how hydrocarbons in different fractions differ from each other:

A
  1. viscosity - longer hydrocarbons have higher viscosity, thick
  2. ignition - shorter hydrocarbons are easy to ignite as they have lower boiling points = often gas at room temp. = gas molecules mix with o2 and produce gas mixture = flames if meets spark,
    -longer hydrocarbons are often liquid at room temp. = higher boiling points = harder to ignite
  3. boiling points - intermolecular forces of attraction break easier in small molecules than bigger molecules = forces are stronger with bigger molecules, big molecules have higher boiling points than smaller molecules
  4. longer hydrocarbon molecules = higher boiling points so near bottom
    - each fraction contains hydrocarbons (mostly alkanes) with similar numbers of carbon atoms = all molecules of fraction will have similar properties = behave in similar ways
  • mostly members of the ALKANE homologous series
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11
Q

Explain an homologous series as a series of compounds which

A
  • have the same general formula
  • similar chemical properties
  • differ by CH2 molecular formula from neighbouring compounds
  • show a gradual variation in physical properties, as exemplified by their boiling points (ex bigger molecule = higher boiling point)
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12
Q

Describe the complete combustion of hydrocarbon fuels as a
reaction in which

A
  • carbon dioxide and water are produced
  • energy is given out (makes it exothermic)
    (- in oxygen)
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13
Q

Explain why the incomplete combustion of hydrocarbons can
produce carbon and carbon monoxide

A
  • not enough oxygen for complete combustion = incomplete combustion
    (ex can happen in appliances like boilers that use carbon compounds as fuels)
  • products of incomplete combustion contain less oxygen than carbon dioxide
  • as well as carbon dioxide and water incomplete combustion produces carbon monoxide (toxic gas and carbon in form of soot)
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14
Q

Explain how carbon monoxide behaves as a toxic gas

A
  • can combine with red blood cells and stop blood carrying oxygen around body
  • lack of oxygen in blood supply to brain = fainting, coma or death
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15
Q

Describe the problems caused by incomplete combustion
producing carbon monoxide and soot in appliances that use
carbon compounds as fuels

A
  • during incomplete combustion tiny particles of carbon can be released into atmosphere
  • when fall to ground = soot
  • soot = buildings dirty, reduces air quality, cause or worsen respiratory problems
    (get incomplete combustion in some appliances that use carbon compounds as fuels)
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16
Q

Explain how impurities in some hydrocarbon fuels result in the
production of sulfur dioxide

A
  • impurities in hydrocarbon fuels = sulfur dioxide when fuels are burned
  • fossil fuels are burned - release co2 and other harmful gases (especially sulfur dioxide and various nitrogen oxides)
  • sulfur dioxide comes from sulfur impurities in fossil fuels
17
Q

Explain some problems associated with acid rain caused when
sulfur dioxide dissolves in rain water

A
  • acid rain causes lakes to become acidic and many plant and animals die
  • acid rain kills trees, damages limestone buildings and stone statues, metal corrodes
  • acid rain forms when sulfur dioxide mixes with clouds and forms dilute sulfuric acid = falls as acid rain
18
Q

Explain why, when fuels are burned in engines, oxygen and
nitrogen can react together at high temperatures to produce
oxides of nitrogen, which are pollutants

A
  • oxygen and nitrogen from the air can react together at high temperatures to produce oxides of nitrogen
    • caused by energy released in combustion reactions (ex internal combustion of cars
    • nitrogen is present in fuels but high temps and pressure inside car engine = nitrogen and oxygen in air to react together
  • nitrogen oxides are harmful pollutants - contribute to acid rain and photochemical smog (type of air pollution = breathing difficulties)
19
Q

Evaluate the advantages and disadvantages of using hydrogen,
rather than petrol, as a fuel in cars

A
  • adv = clean fuel = hydrogen combines with oxygen to produce energy so only waste product is water (no pollutants or toxic carbon monoxide or soot produced when fossil fuels are burnt)
    = renewable resource, can also be obtained from water produced by cell when its used in fuel cells
  • dis = special, expensive engine
    = expensive to manufacture hydrogen gas, uses lots of energy from another source (ex burning fossil fuels = pollutants)
    = hard to store, not widely available
20
Q

what fossil fuels are non-renewable and where ae they obtained from

A

-petrol, kerosene, diesel oil are obtained from crude oil
- methane is a non-renewable fossil fuels found in natural gas

21
Q

Explain why cracking involves the breaking down of larger,
saturated hydrocarbon molecules (alkanes) into smaller, more
useful ones, some of which are unsaturated (alkenes)

A
  • form of thermal decomposition (when one substance breaks down into at least 2 new ones when heated)
    • this breaks strong covalent bonds so you need lots of energy, catalyst often used to speed it up
  • lots of longer molecules (produced from fractional distillation) are cracked into smaller ones as there is more demand for products like petrol and diesel than bitumen and fuel oil
  • cracking also produces lots of alkene molecules which can be used to make polymers (mostly plastics)
22
Q

Explain why cracking is necessary

A
  • cracking turns long saturated (alkane) molecules into smaller unsaturated (alkene) and alkane molecules (more useful)
  • breaks down long hydrocarbons into smaller more useful hydrocarbon molecules
  • cracking helps balance availability of fractions with demand for them
23
Q

type of bonds do alkanes have

A

single covalent bonds

24
Q

type of bonds do alkenes have

A

at least one carbon - carbon bond
-double bond

combined chemistry (9 decks)

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