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EdExcel GCSE Chemistry > Fuels - Topic 8 > Flashcards

Fuels - Topic 8 Flashcards

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1
Q

Hydrocarbons:

A

compounds that contain carbon and hydrogen only

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2
Q

What is crude oil?

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

Explain the change in boiling points of alkanes:

A
  • boiling points increase as length of chain increases
  • as the chain is longer so there are more places for IMFs so more forces to be broken
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4
Q

What does crude oil contain and how can these substances be separated?

A
  • crude oil is a mixture which contains a large number of different liquids which have dif. boiling points
  • these types of mixtures can be separated by fractional distillation
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5
Q

The easier something is to boil…

A

the more flammable it is

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6
Q

As the boiling points of the fractions increases what happens to their properties?

A
  • appearance darkens
  • ease of lighting becomes more difficult
  • smokiness of the flame increases
  • viscosity (stickiness) increases
  • thicker liquids and not runny
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7
Q

How is crude oil separated by fractional distillation in the lab?

A
  • if crude oil is heated the liquids with the lowest bp’s will evaporate first and pass up the flask and fractionating column
  • this vapour then passes down the side-arm and through the condenser
  • this cools down the vapour and so it eventually condenses as a liquid which forms in the conical flask
  • if the mixture is heated very gently between a number of temp ranges - different liquids can be collected at dif. temps - these are called fractions
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8
Q

How is crude oil separated by fractional distillation industrially?

A
  • crude oil is heated/boiled and then it enters the fractionating column
  • as they rise up the column the temp becomes lower
  • when the temps becomes just below the bp of the a substance that substance will melt and a liquid will be collected in a tray at that level in the column
  • at different levels a mixture of liquids called fractions are collected - fractions will consist of a mixture of liquids containing similar sized molecules with similar boiling points
  • substances with low boiling points will remain gases even at the top of the column as the temp is higher than their boiling points
  • these gases are called petroleum gases and will be composes of the shorter chains of alkanes e.g. ethane, methane, propane etc.
  • some v. long alkanes are still liquid even at high temps as the both of the column - this fraction is called residue
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9
Q

Uses of (petroleum) gases:

A
  • domestic heating
  • cooking
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10
Q

Uses of petrol:

A

fuel for cars

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11
Q

Uses of kerosene:

A

fuel for aircraft

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12
Q

Uses of diesel oil:

A

fuel for some cars and trains

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13
Q

Uses of fuel oil:

A
  • fuel for large ships
  • used in some power stations
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14
Q

Uses of bitumen:

A
  • surface roads - tar
  • roofs
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15
Q

Examples of some fractions of crude oil:

A
  • (petroleum) gases
  • petrol
  • kerosene
  • diesel oil
  • fuel oil
  • bitumen
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16
Q

Organic compound:

A

compounds which contain carbon

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17
Q

Homologous series:

A

a group of chemical compounds which share certain characteristics

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18
Q

What do compounds in the same homologous series share?

A
  • each compound had the same functional group and therefore the same general formula
  • have similar chemical properties
  • differ by CH2 units in molecular formulae from neighbouring compounds
  • show gradual trend in physical properties (as exemplified by their boiling points)
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19
Q

The complete combustion of hydrocarbon fuels is a reaction in which…

A
  • CO2 and H2O are produced
  • energy is given out - exothermic
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20
Q

Which alkanes are used as fuels and why?

A

the shorter alkanes are used as fuels are they react easily with oxygen

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21
Q

When does complete combustion take place?

A

when an alkane burns in sufficient oxygen

22
Q

Balanced equation for complete combustion of ethane:

A
23
Q

Balanced equation for complete combustion of hexane:

A
24
Q

How can impurities in some hydrocarbon fuels result in the production of sulphur dioxide?

A
  • most fuels inc. coal, carbon and/or hydrogen may also contain some sulphur
  • when the fuels are burnt in oxygen this sulphur can react with the oxygen to form sulphur dioxide
25
Q

How is acid rain caused?

A

when sulphur dioxide dissolves in rain water

26
Q

What are the problems with acid (sulphuric acid) rain?

A
  • damages buildings and statues (made of limestone)
  • reduces the growth of or kills trees and crops
  • cause pH of water tables to be lower which kills fish
27
Q

What happens when fuels are burned in engines?

A
  • When burned in engines at high temperatures nitrogen and oxygen from the air combine to produce nitrogen monoxide
  • When this nitrogen monoxide is released from vehicle exhaust systems, it combines with oxygen in the air to form nitrogen dioxide
  • nitrogen monoxide and nitrogen dioxide are pollutants
28
Q

Advantages of using hydrogen as a fuel in cars rather than petrol:

A
  • Use of hydrogen – petrol is from crude oil, a finite resource
  • Only produces water – no CO2 produced which contributes to global warming
29
Q

Disadvantages of using hydrogen as a fuel in cars rather than petrol:

A
  • Expensive
  • Difficult to transport and store hydrogen - as H2 takes up a lot of space since it is a gas
  • Dangerous – hydrogen can be explosive
30
Q

What are petrol, kerosene, diesel oil and methane?

A

non-renewable fossil fuels

31
Q

Where are petrol, kerosene and diesel oil obtained from?

A

obtained from crude oil

32
Q

Where is methane obtained from?

A

found in natural gas

33
Q

What does the fractional distillation of crude oil provide in general?

A

fractional distillation of crude oil provides a surplus of the long chain hydrocarbons e.g. decane but a shortage of short chains hydrocarbons e.g. methane

34
Q

What does cracking involve?

A

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

35
Q

What type of reaction is the cracking of hydrocarbons?

A

thermal decomposition

36
Q

General cracking equation:

A

longer alkane → shorter alkane + short-chain alkene

37
Q

What is the process of cracking?

A
  • Hydrocarbons can be cracked to produce smaller, more useful molecules
  • heat the hydrocarbons to vaporise them
  • the vapours are then:
    • either passed over hot catalyst
    • mixed with steam and heated to a v. high temp so that thermal decomposition reactions can occur
38
Q

What are the products of cracking?

A

alkanes + alkenes (unsaturated hydrocarbons)

39
Q

Why is cracking necessary?

A
  • vital process as it converts long chain molecules which are less useful into short chain molecules which are more useful
  • demand for smaller chained alkanes is much greater for longer chained alkanes as they are more useful - demand > supply
  • shorter chained hydrocarbons ignite more easily and so are more useful as fuels
40
Q

When does incomplete combustion take place?

A

Incomplete combustion happens when the supply of air or oxygen is poor

41
Q

How much energy is released in incomplete combustion?

A

Less energy is released than during complete combustion

42
Q

Products of incomplete combustion:

A
  • carbon monoxide
  • carbon (soot)
  • water
43
Q

Incomplete combustion of propanol example:

A

C3H8 + 3O2 → 2CO + C + 4H2O

44
Q

What is the carbon released as in incomplete combustion?

A

carbon is released as fine black particles (soot)

45
Q

Harmful impacts of soot:

A
  • Soot can cause breathing problems and it blackens buildings
  • It may block boilers and other appliances, or cause a fire
46
Q

Harmful impacts of carbon monoxide:

A
  • Carbon monoxide is a toxic gas
  • It is absorbed in the lungs and binds with the haemoglobin in the red blood cells - this reduces the capacity of the blood to carry oxygen
  • Carbon monoxide causes drowsiness, and affected people may fall unconscious or even die
47
Q

Why can the incomplete combustion of hydrocarbons produce carbon and carbon monoxide?

A

less oxygen so carbon atoms cannot be completely oxidised to produce CO2 instead CO and O are produced

48
Q

Why can the incomplete combustion of hydrocarbons produce carbon and carbon monoxide?

A
  • If there’s not enough oxygen, some of the fuel doesn’t burn – this is partial
    combustion
  • solid particles of soot (carbons) and unburnt fuel are released
  • Carbon monoxide (CO) is also released when there isn’t enough oxygen to produce CO2 instead
49
Q

How does carbon monoxide behave as a toxic gas?

A

carbon monoxide is a colourless and odourless gas which, if breathed in, prevents red blood cells carrying oxygen around your body, which leads to death

50
Q

What problems can be caused by the incomplete combustion producing carbon monoxide and soot in appliances that use carbon compounds as fuels?

A
  • Carbon monoxide causes health problems
  • Soot causes global dimming

EdExcel GCSE Chemistry (29 decks)

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