Topic 8 – Fuels and Earth Science Flashcards
What is a hydrocarbon
● Hydrocarbons are compounds that contain carbon and hydrogen only
Describe crude oil
● 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
Describe and explain the separation of crude oil into simpler, more useful mixtures by the process of fractional distillation
Crude oil is a mixture of different hydrocarbons, different hydrocarbons have different boiling points (longer chain hydrocarbons have higher boiling points)
● The crude oil is heated in the fractionating column and the oil evaporates and condenses at a number of different temperatures.
● The fractionating column works continuously, heated crude oil is piped in at the bottom. The vaporised oil rises up the column and the various fractions are
constantly tapped off at the different levels where they condense.
● The fractions can be processed to produce fuels and feedstock for the petrochemical industry.
Recall the names and uses of the following fractions
● Gases: domestic heating and cooking
● Petrol: fuel for cars
● Kerosene: fuel for aircraft
● Diesel oil: fuel for some cars and trains
● Fuel oil: fuel for large ships and in some power stations
● Bitumen: surface roads and roofs
Explain how hydrocarbons in different fractions differ from each other
● Some properties of hydrocarbons depend on the size of their molecules. These properties influence their use as fuels.
● Shorter the molecules, the less viscous it is. (more runny) and the longer the molecules, the more viscous it is.
● The shorter the molecules, the lower the temperature at which that fraction evaporates or condenses – and the lower its boiling point.
● The shorter the molecules – the more flammable it is, so the easier it is to ignite
What is a homologous series
Aseries of compounds which:
● Have the same general formula
● Differ by CH2 in molecular formulae from neighbouring compounds
● Show a gradual variation in physical properties, as exemplified by their boiling points
● Have similar chemical properties
Describe the complete combustion of hydrocarbon fuels
A reaction in which:
● The hydrocarbon reacts with O2 and CO2 and H2O are produced
● Energy is given out (exothermic)
Explain why the incomplete combustion of hydrocarbons can produce carbon and carbon monoxide
● If there’s not enough oxygen, some of the fuel doesn’t burn – this is partial combustion. Here, 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
Explain how carbon monoxide behaves as a toxic gas
● 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
Describe the problems caused by incomplete combustion producing carbon monoxide and soot in appliances that use carbon compounds as fuel
● Carbon monoxide causes health problems
● Soot causes global dimming
Explain how impurities in some hydrocarbon fuels result in the production of sulfur dioxide
● Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur
● when the fuels are burnt in oxygen, this sulfur can react to form sulfur dioxide
Explain some problems associated with acid rain (caused when sulfur dioxide dissolves in rain water)
● Damages buildings and statues (made of limestone)
● Reduce the growth of or kill trees and crops
● Lower pH of water in lakes, killing fish
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
● 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
Advantages and disadvantages of using hydrogen, rather than petrol, as a fuel in cars
● Advantages
○ Use of hydrogen – petrol is from crude oil, a finite resource
○ Only produces water – no CO2 produced which contributes to global warming
● Disadvantages
○ Expensive
○ Difficult to transport and store hydrogen
○ Dangerous – hydrogen can be explosive
Recall that petrol, kerosene and diesel oil are…
● Non-renewable fossil fuels obtained from crude oil
● And methane is a non-renewable fossil fuel found in natural gas
Explain how cracking involves the breaking down of larger, saturated hydrocarbon molecules (alkanes) into smaller, more useful ones, some of which are unsaturated (alkenes)
● Hydrocarbons can be cracked to produce smaller, more useful molecules. This process involved heating the hydrocarbons to vaporise them.
● The vapours are:
○ Either passed over a hot catalyst
○ Mixed with steam and heated to a very high temperature so that thermal decomposition reactions can occur.
● The products of cracking include alkanes and unsaturated hydrocarbons called alkenes
Alkenes
○ Alkenes have the general formula CnH2n
○ The first 2 alkenes are ethene and propene.
○ they are unsaturated because they have a double bond
Why is cracking necessary?
● Demand for smaller chained alkanes is much greater than that for longer chained alkanes
● shorter chained hydrocarbons ignite more easily and so are more useful as fuels
What gases produced the Earth’s early atmosphere?
● There was intense volcanic activity that released gases that formed the early atmosphere
○ At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus today, mainly CO2 with little or no O2(g)
○ Volcanoes also produced nitrogen which gradually built up in the atmosphere & there may have been small proportions of methane (CH4) and NH3
Describe that the Earth’s early atmosphere was thought to
contain
● Little or no oxygen
● A large amount of CO2
● Water vapour
● Small amounts of other gases
Explain what the oceans were formed from?
● Water vapour condensed to form the oceans – H2O (g) -> H2O (l)
Explain how the amount of CO2 in the atmosphere was decreased when CO2 dissolved as the oceans formed
● CO2 dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of CO2 in the atmosphere
Explain how the growth of primitive plants changed the composition of gases in the atmosphere?
● Algae & plants produced the O2 that is now in the atmosphere by photosynthesis:
carbon dioxide + water –(light)-> glucose + oxygen
● Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere
● Over the next billion years plants evolved and the % oxygen gradually increased to a level that enabled animals to evolve
● Algae and plants decreased the % CO2
in the atmosphere by photosynthesis
Describe the chemical test for oxygen (O2)
● Uses a glowing splint inserted into a test tube of the gas
o Splint relights in oxygen
What gases are involved in the greenhouse effect?
methane
water vapour
carbon dioxide.
What is the greenhouse effect?
Some gases in the Earth’s atmosphere stop heat radiating into space from the Earth. This is called the greenhouse effect and the gases involved are called greenhouse gases.
Explain the greenhouse effect
● Electromagnetic radiation at most wavelengths from the sun passes through the Earth’s atmosphere
● The Earth absorbs some radiation and thus warms up (essential for life on Earth). But some heat is radiated from the Earth as infrared radiation.
● Some of this IR radiation is absorbed by greenhouse gases in the atmosphere
● Atmosphere warms up leading to the greenhouse effect and global warming
Examples of human activity include which increase levels of CO2 & CH4
● Activities increase levels of CO2 & CH4
● Examples of human activity include:
o Driving (CO2)
o Consuming electricity (CO2)
o Raising livestock (cows – CH4)
o Decay of organic waste in landfill sites (CH4)
The potential effects on the climate of increased levels of CO2 and CH4
● Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface
and that this will result in global climate change
Describe the effects on the climate may be mitigated
o It is difficult to model such complex systems as global climate change.
o This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.
