KS3 Science Quizzes

GCSE KS4 Science-Chemistry

Advanced Level Chemistry

docboilproducts updated Feb 15th 2008

The SEPARATION of the crude oil mixture into fractions and the USES of these fractions

A fraction is a mixture of a restricted boiling point range of molecules, they have a similar number of carbon atoms and physical properties. The uses of the fractions depend on their physical and chemical properties.

• Hydrocarbon molecules are only  made of a chemical combination of carbon and hydrogen atoms.

• They are compounds because they consist of atoms of at least two different elements.

• Crude oil is a complex mixture of mainly hydrocarbon compound molecules. A mixture consists of two or more elements or compounds which are not chemically combined. The chemical properties of each substance in the mixture is unchanged.
• This means crude oil can be separated by physical methods, in this case by fractional distillation, because they have different boiling and condensation points.
• The crude oil is heated to vapourise it (evaporated or boiled).
• The most volatile fraction, i.e. the molecules with the lowest boiling points, boil or evaporate off first and go to the top of the column.
• The rest separate out according to their boiling/condensation point so that the highest boiling fraction, i.e. the less volatile molecules with higher boiling points, tend to condense more easily lower down the column.
• The bigger the molecule, the greater the intermolecular attractive forces between the molecules, so the higher the boiling or condensation point (see physical property trends).
• Note: Covalent chemical bonds like C-C or C-H are not broken in the process, only the intermolecular force of attraction is weakened to allow the initial evaporation or boiling.

More on relating the physical properties of the fractions to their uses and dangers

 Down the list above the molecule gets ...

1. ... bigger as the carbon atom number in the molecule increases.

2. ... more viscous as the intermolecular attractive forces* between molecules increases, these forces always increase the bigger the molecule in a series of molecules of similar structure.

   • * Note for advanced students - these are non-polar weak electrical attractive Van der Waals forces, correctly described as instantaneous dipole - induced dipole forces.

3. ... higher melting point as more vibrational kinetic energy is needed to overcome the intermolecular attractive forces holding the molecules together to form the crystals.

4. ... higher boiling point as more particle kinetic energy is needed to overcome the increasing intermolecular forces* between the liquid molecules.

   • Trends 3. and 4. are readily appreciated e.g. methane gas (CH₄), liquid petrol (about C₅H₁₂ to C₇H₁₆) and solid candle wax (over C₂₁H₄₄).

5. ... less flammable as they become less volatile, again due to increasing intermolecular forces*.

   • This raises health and safety issues about handling, distributing and storing flammable hydrocarbons. The smallest molecules (natural gas to petrol) are the most volatile and therefore the most easily ignited. Any naked flame or spark could set off a fire and explosion and even

• The refinery gas fractions, can be stored under pressure, and because the gas readily flows, it can be conveniently pumped to burner systems, but it is easily ignited and explosive.
• Vehicle fuels like petrol must be liquid for compact and convenient storage but they must be easily vapourised to mix with air in the engine prior to ignition. The ease of vaporisation does however make them flammable!
• Paraffin and kerosine are less flammable and safer, but not as easily ignited.
• Fuel oil is not too viscous to pump to a central heating burner for domestic use. It is not very volatile and so not as flammable and dangerous to use as petrol or diesel etc.
• Lubricating oil must be quite viscous to stick onto surfaces. Smaller molecules might be more runny but they would evaporate away! It is also water repellent and helps reduce corrosion on moving machine parts.
• Candle wax is very convenient as a solid for humble lamp (especially in power cuts!), but via a wick, the heat from the flame is sufficient to vaporise the hydrocarbons to burn them.
• Bitumen is a water repellent solid at room temperature but is readily melted (sometimes too easily in hot weather). Used as base for a road chipping top surface or sometimes directly. It is also used to waterproof roofing felt.

The complete combustion of hydrocarbons (excess air)

Introduction

• The fuel coal consists mainly of carbon, which, if burned/ignited in excess air, combusts to form carbon dioxide.

  • carbon + oxygen ==> carbon dioxide

  • C_(s) + O_2(g) ==> CO_2(g)

  • This is what you expect to happen in an open domestic coal fire.

• If not enough air/oxygen is available, coal will only 'half' burn to form the deadly odourless, colourless and toxic gas carbon monoxide.

  • 2C_(s) + O_2(g) ==> 2CO_(g)

  • This can happen if organic material, coal or peat is smouldering underground and is obviously a dangerous situation.

  • If it was formed in a domestic coal fire it will quite happily burn with a pale blue flame to form the 'safe' combustion gas carbon dioxide.

  • 2CO_(s) + O_2(g) ==> 2CO_2(g)

• The diagram shows how to detect the products of hydrocarbon combustion e.g. burning candle wax.

• When hydrocarbons are burned in air a fast exothermic reaction occurs releasing heat and forming carbon dioxide and water.

• It is an oxidation reaction due to O gain by C and H.

• The carbon dioxide is chemically detected with limewater - with which it forms a white precipitate (milky appearance) of calcium carbonate.

• The water is chemically detected either by (i) anhydrous white copper sulphate turning blue OR (ii) dried blue cobalt chloride paper turning pink.

• A physical test for water is to measure its boiling point (should be 100^oC).

When a hydrocarbon molecule (reactant) burns in an excess of air-oxygen their are only two products of the reaction. The carbon atoms are oxidised on combining with oxygen to form carbon dioxide molecules, and the hydrogen atoms are oxidised to water molecules ('hydrogen oxide'). This section ignores the combustion of the pollutant sulphur.

general word equation: hydrocarbon + oxygen ==> carbon dioxide + water

word equations e.g. methane + oxygen ==> carbon dioxide + water

and the corresponding symbol equation is CH_4(g) + 2O_2(g) ==> CO_2(g) + 2H₂O_(l)

Note that one CO₂ for every C, and one H₂O for every two H's in the hydrocarbon molecule.

In terms of displayed formula the equation would be written as ...

... in which every individual atom is shown and how it is bonded ('connected') with other atoms in the molecule. All the dashes represent the covalent bonds between the atoms in the molecules.

Another example is the combustion of propane ...

propane + oxygen ==> carbon dioxide + water

C₃H_8(g) + 5O_2(g) ==> 3CO_2(g) + 4H₂O_(l)

and in terms of displayed formula and balancing numbers ...

and the above diagrams show how the atoms have rearranged themselves in the reaction after the reactant bonds are broken (C-H, O=O and C-C in ethane etc. below)) and the new bonds formed in the products (C=O and O-H). Note the number of atoms of each element must be the same on each side of the equation (1C, 4H's and 4 O's, Law of Conservation of mass) and the products are different substances with different properties compared to the reactants. See Elements, Compounds and Mixtures page for more on writing and balancing equations.

for ethane the more awkward symbol equation is ...

2C₂H_6(g) + 7O_2(g) ==> 4CO_2(g) + 6H₂O_(l)

and for pentane the symbol equations is ...

C₅H_12(l) + 8O_2(g) ==> 5CO_2(g) + 6H₂O_(l)

The reaction of alkanes with chlorine is described on the Extra Organic Chemistry page

Atmospheric pollution Part-1: The Incomplete Combustion of hydrocarbons CO

• If there is not enough oxygen present to completely burn the fuel to carbon dioxide and water other products may form causing pollution and fuel inefficiency.

• The most common partially burned products are likely to be carbon C (soot) and deadly carbon monoxide CO.

  • Carbon-soot, a fine black powder-dust is potentially harmful and readily formed in fires i.e. its classically produced by smoky yellow flames. The soot, like any fine solid 'dust' is harmful when absorbed on the sensitive tissue of the linings of the nose, throat and lungs. Soot deposits cause coughing and sore throat and are ejected from your body through sneezing, coughing, and nose blowing. Coarse particles (10 microns) are inhaled into your windpipe and settle there, causing irritation and more coughing.  Soot is also a 'carrier' of polycyclic aromatic hydrocarbons (PAH's) on it which are carcinogenic.

  • Even very low concentrations of carbon monoxide can be fatal. Why? Oxygen is carried around the body by a complicated protein molecule in red blood cells called haemoglobin. The bonding between oxygen and haemoglobin is quite weak to allow easy oxygen transfer for cell respiration. Unfortunately, the bonding between carbon monoxide and haemoglobin is stronger, so oxygen is replaced by carbon monoxide and blocks normal cell respiration. The consequences are reduced blood oxygen concentration leading to unconsciousness and eventually death!

• It would appear that the hydrogen in the fuel molecules is more easily burned and usually forms water so the equations for incomplete combustion below show the formation of carbon-soot and carbon monoxide when there is a lack of oxygen for complete combustion.

• There is also less heat released compared to complete combustion.

  • e.g. CH_4(g) + O_2(g) ==> C_(s) + 2H₂O_(l)

  • and 2CH_4(g) + 3O_2(g) ==> 2CO_(g) + 4H₂O_(l)

• Therefore it is extremely important that any combustion system is as efficient as possible e.g. gas heaters, furnaces etc. must all have excellent ventilation for complete combustion to harmless water and carbon dioxide.

• If there is any smell of gas, make sure (i) all appliances are turned off, (ii) all sources of ignition are absent, and (iii) ring the gas board!

• Faulty gas appliances have led to tragic deaths. Carbon monoxide is colourless and odourless and even low concentrations in the air can be fatal. It also accounts for why long road tunnels need to be well ventilated too.

• Carbon monoxide is unfortunately emitted by all car exhausts, though catalytic converters help reduce this by converting nitrogen monoxide (another pollutant, see below) and carbon monoxide into harmless nitrogen and carbon dioxide.

  •   2NO_(g) + 2CO_(g) ==> N_2(g) + 2CO_2(g)

• See also pollution Part 2 Plastics and Part 3 Oil Industry and products in general.

Energy resource evaluation - What makes a good fossil fuel?

Factors that should be taken into consideration

• Energy value: e.g. kJ of heat energy released per kg;

• Availability: Geographical convenience, oil production levels;

• Storage: Health and safety issues e.g. coal very safe, natural gas more dangerous

• Cost: Extraction, transport, market price

• Toxicity and Pollution: Greenhouse effect (which produces the least or most CO₂/energy released?); sulphur content of fuel (most removed before fuel used to minimise sulphur dioxide and acid rain formation); efficiency of combustion e.g. minimum carbon monoxide and soot levels

• Ease of use: Transferred easily e.g. oil and gas readily piped around and readily ignited for a quick start in power station. Coal is more trouble to transport and does not ignite as easily.

• See also: Extra Organic Chemistry page and  Some other ideas for alternative fuels (page originally designed for AS level).

Alkenes are hydrocarbons containing a carbon...carbon double bond (>C=C<) as well as single bonds. These are called unsaturated molecules because two atoms can join onto the bond when it opens up. The first two in the series are shown below. They are extremely reactive and important compounds in the chemical industry and are converted into very useful compounds e.g. plastics. They are made from cracking processes (see below)

(1) is the molecular formula: a summary of the totals of each atoms of each element in one molecule; (2) is a 'shorthand' version of the structural or displayed formula (3); (3) is called the structural or displayed formula: it shows how all the atoms are linked with the covalent bonds -

• Hydrocarbons are colourless. Bromine dissolved in water or trichloroethane solvent forms an orange (yellow/brown) solution.
• When bromine solution is added to both an alkane or an alkene the result is quite different.
• The alkane solution remains orange - no reaction.
• However, the alkene decolourises the bromine as it forms a colourless dibromo-alkane compound - see equations.

  .... or

ethene + bromine ==> 1,2-dibromethane

• Alkenes are unsaturated molecules, atoms can add to them via the C=C double bond, so a reaction occurs.

• Alkanes are saturated - no double bond - and atoms cannot add - so no reaction.

propene + bromine ==> 1,2-dibromopropane

  H₂

propene + hydrogen ==> propane

• Alkenes will react with hydrogen gas over a nickel catalyst.

• The reaction process is used to make margarine from vegetable oils.

CRACKING a problem of Supply and Demand!

There isn't enough petrol in crude oil and crude oil doesn't have any alkenes in it for plastics but cracking reactions can help!

• When crude oil has been distilled into useful fractions it is found that the quantities produced do not match the ratio required for commercial needs e.g. we have an insatiable appetite for petrol and diesel in our cars and there are two many left-overs of the larger molecules which do not make good fuels or have other uses. Fuel oil, naphtha and bitumen in crude oil exceed demand.

• Also, alkenes are not found in crude oil and they one of the most valuable types of organic molecule in the chemical industry e.g. to make polymers (plastics) or ethanol (an alcohol).

• The two deficiencies are remedied by the process of cracking which converts useless big molecules into useful smaller ones.

• CRACKING is done by heating some of the less used fractions to a high temperature vapour and passing over a suitable hot catalyst. The cracking reaction is an example of thermal decomposition - a reaction that breaks down molecules into smaller ones using heat. The main products from cracking alkanes from oil are smaller alkanes (e.g. for petrol or diesel) and alkenes (e.g. for plastics).

• The equations below illustrate the process, small molecules are used to show the overall molecular change clearly BUT in practice the 'starter' molecules are likely to be more those shown in equations (3) and (4). The cracking involves breaking single carbon-carbon bonds to form the alkanes (saturated hydrocarbons) and alkenes (unsaturated hydrocarbons) products.

(1)

butane ethane ethene.....or

(2)

butane methane propene

(3) C₈H₁₈ C₆H₁₄ + C₂H₄ (making petrol molecule + ethene)

(4) C₁₂H₂₆ C₉H₂₀ + C₃H₆ (making diesel molecule + propene)

The formation of POLYMERS and the USES of PLASTICS - Macromolecules

Reactions of alkenes (3) polymerisation/polymerization

(a few more points on Extra Organic page)

The formation of big polymer molecules called polyalkenes from small molecules called alkenes

• When catalysed and heated under pressure, unsaturated alkenes link together when 'half' of the double bond opens. The spare bonds are used to join up the molecules. The general equation for polyalkene formation is shown in the diagram above.

• The original small molecule is called the monomer and the long molecule is called the polymer, which is the sort of molecule most plastics consist of. The polymer is now a saturated molecule but has the same C:H ratio as the original alkene.

• So lots of small molecules join up to form a big long molecule in a process called addition polymerisation and the polymers are named as poly(name of original alkene), i.e. poly(alkene) and several examples are shown below.

poly(ethene

Poly(ethene) from ethene is a cheap but very useful plastic used for plastic bags and bottles (old or commercial names: polyethylene, polythene and polyethene).

poly(propene)

Poly(propene) from propene is stronger and more hard wearing than polythene and is used for making crates, fibres and ropes (old or commercial names: polypropylene, polyprene and polypropene).

poly(chloroethene), pVC

Poly(chloroethene), PVC, made from chloroethene (old name vinyl chloride) is much tougher than poly(ethene) and very hard wearing with good heat stability. so it is used for covering electrical wiring and plugs. It is also replacing metals for use as gas and water drain pipes and has found a use as artificial leather and readily dyed to bright colours! (old names : polyvinyl chloride, shortened to PVC)

Polystyrene^* is made from styrene^* (another alkene monomer) and is used in a gas expanded form for packaging and insulation. [^*new names: poly(phenylethene) polymer made from phenylethene monomer]

1. Polymers or plastics cannot be easily broken down by micro-organisms i.e. most, at the moment, most are NOT biodegradable which leads to waste disposal problems and 'non-rotting' litter around the environment.

   • Land-fill sites are getting full and recycling isn't as easy as it may seem . (see 3.)

   • Incineration i.e. using waste plastic as fuel must be very efficient to avoid any other pollution problem. (see 2.)

2. When plastic materials burn they can produce highly toxic gases such as carbon monoxide, hydrogen cyanide and hydrogen chloride (particularly from PVC and other plastics containing chlorine and nitrogen). The toxic fumes cause deaths in house fires and controversial problems with alleged inefficient waste incinerators as they will definitely cause environmental problems if burned on waste tips!

3. It is difficult to recycle plastics because of separation into the various types of polymer and their different physical properties. BUT this should not prevent us from trying and it would be beneficial to prolong the life of the finite crude oil reserves AND reduce pollution and space in land-fill sites.

   • However, people are coming up with ideas. A company in Scarborough, England, is collecting waste plastic. This is shredded and compressed into porous pads and used for good 'underground' drainage layers for footpaths, golf greens and sand bunkers etc. and has a good working life because the material isn't biodegradable!

   • New plastics are being developed which are more biodegradable or can be recycled, so will the paper bag and cardboard package make a comeback? (in Ireland you have to bring your own bag or buy one, and not necessarily a plastic one!).

   • It is possible in some cases to break the plastic material down with heat (a sort of 'cracking') into smaller organic hydrocarbon molecules that can act as chemical feedstock like oil, from which you can make other valuable products including plastics.

4. See also pollution Part 1 Carbon monoxide and Part 3 Oil Industry and products in general.

Other very useful products from oil - despite the negative aspects!

As well as plastics, there are lots of other useful compounds which can be made from the carbon based molecules of oil, e.g. look up drugs/esters on the extra GCSE organic chemistry page. Most are only dealt with at a more advanced level but the structural material, pharmaceutical and food industries have all developed a wide range of products in attempt to enhance our lifestyle and quality of life.

More on Oil Products and Environment Problems

(see also plastics above)

• 'COSTS'?: Our economy, like many other countries has become very dependent on the extraction, sale and use of oil based products. BUT, there is high price to be paid at times whether it be pollution effects or warring countries with oil economics factors.

• ACCIDENTS: Oil rig accidents, broken pipelines, oil tanker wrecks etc. all have terrible effects on the plant and animal life of the locality as we see from the horrible TV pictures of seabirds coated in oil, and toxic oil slicks covering the beaches and sands. There is also the risk to humans from fires and explosions on rigs or at oil refinery installations and fuel storage depots etc.

• RISING CARBON DIOXIDE LEVELS:

• 

  • The graph shows the steady rise in the concentration of carbon dioxide in the atmosphere from 1959-2004 as measured at the Mauna Loa mountain top observatory on the Pacific island of Hawaii.

  • It is a good base-line for our planet because it is well away from any industry involving fossil fuel burning.

  • The concentration of CO₂ is in ppm (parts per million).

  • 1ppm means 1 in 10⁶ of air molecules is CO₂. In % volume terms, 1 ppm = 100 x 1 / 10⁶ = 0.0001%.

  • The graph shows that the CO₂ has risen from 0.0316% (316 ppm) in 1959 to 0.0378% (378 ppm) in 2004.

  • This doesn't seem much of an increase, BUT on a global scale, the extra 'Greenhouse CO₂ Gas' could have drastic consequences (see next paragraph), but the computer model predictions have a high degree of uncertainty.

  • I've started a new page of extra material e.g. graphs, explanations and discussion points on Global Warming. More work will be done on it as I learn more myself.

• THE GREENHOUSE EFFECT: The burning of oil and other fossil fuels is contributing to the 'Greenhouse Effect' or global warming. The Earth's land-water surfaces absorbs the Sun's radiation in the form of infra-red (main heating effect) and visible/ultraviolet sunlight. Carbon dioxide and other gases including methane, water vapour and CFC's absorb the re-radiated lower frequency infrared energy from the Earth's surface and so warming the atmosphere, rather like a greenhouse allows the sunlight in but not out. The effects are predicted to be dramatic e.g. rising sea levels as polar ice melts causing flooding in low lying land, more energy in the global weather system leads to more frequent violent weather patterns etc. etc. (see further note from IPCC report 2007) BUT there is considerable uncertainty as to what might actually happen!

  • What can we do about it? i.e. how can we reduce our 'carbon footprint' to reduce global warming?

    1. Reduce the amount of fossil fuels we burn in power stations, but the international community is struggles to come to an agreement over this issue and the huge, and fast growing economies of India and China are demanding the building of large numbers of fossil fuel power stations (in 2006 China is starting to build one every week!).

    2. 'Green' alternative renewable energy resources can be more exploited e.g. wind, wave and water/hydroelectric power and photovoltaic cells, solar panels in roofs etc. all reduce acid rain pollution and CO₂ production by using less fossil fuels. They are good for domestic and small communities but none at the moment is suitable for large scale energy production for the highly populated countries with large industrial economies.

    3. Like 2., nuclear power is another option that does not produce carbon dioxide and is suitable for large scale power generation, but there are real public fears about the consequences of a nuclear power plant accident (e.g. Chernobyl, Russia in 1986).

    4. Recent ideas include storing the CO₂ from fossil fuel power stations underground in rocks under pressure - but I don't know any details or how feasible it is.

    5. Use less electricity and heat energy from fuel combustion by being careful of its use e.g. increase home insulation and more efficient electrical appliances like 'low energy' light bulbs.

    6. Burning wood is sustainable and the CO₂ formed on its combustion is recycled via photosynthesis BUT (i) it does not burn cleanly, (ii) its energy density is low (heat energy released per mass of fuel) and (iii) no good for large scale power generation.

    7. Global dimming. The more cloud that is formed in the upper atmosphere the more sunlight is reflected, so less radiated energy reaches the Earth's surface, leading to the opposite of global warming. It has been suggested that cloud formation could be encouraged by seeding the atmosphere with crystals to promote cloud formation. It is ironic that the vapour trails of aircraft, with their heavy use of fossil fuels, actually contribute to global dimming as well as to global warming at the same time! The effect of global dimming was noticed in the aftermath of the 9/11 terrorist attacks on New York's World Trade Center Twin Towers in 2001. All aircraft were grounded in the USA and many parts of the world for several days after the attacks and sunlight gauges showed a small but abnormal increase in sunlight levels reaching the Earth's surface. There was also other evidence from monitoring stations which measure rates of water evaporation from large tanks, when a small but abnormal increase in evaporation rate from extra sunlight was noted.

• ACID RAIN: Fossil fuels contain compounds of the element sulphur When the fuel is burned the sulphur compounds also burn to form sulphur dioxide. This is an acidic gas and dissolves in rainwater, it then reacts with water and oxygen to form a very dilute solution of sulphuric acid.

  • sulphur + oxygen ==> sulphur dioxide: S_{(in fuel molecules)} + O_2(g) ==> SO_2(g)

  • Sulphur dioxide is a harmful gas and lung irritant and contributed to 5000 extra deaths in the great 'London Smog' in the 1950's as well as being a major acid-rain gas. It reacts with oxygen (in air) and water (rain) and gets oxidised to form very dilute sulphuric acid - acid rain and the overall change is represented by the equation below.

    • SO_2(g-air) + O_2(g-air) + 2H₂O_(l-rain) ==> 2H₂SO_4(aq-rain)

  • The formation of acid rain has several bad effects on the environment e.g.

    • the low pH causes plant damage, particularly trees,

    • kills certain life forms and so damages eco cycles and food chains in rivers or lakes harming wildlife like trout,

    • increases the 'weathering' corrosion rates of building stone (particularly limestone).

• OTHER POLLUTANTS: High temperature combustion also produces other pollutants including ...

  • Nitrogen oxides collectively denoted by NO_x: NO is formed in car engines and changes to NO₂, which is acidic, contributing further to acid rain (above), and are also involved in the chemistry of 'photochemical smog' - which produces chemicals harmful to respiration, irritating to eyes and contributes to acid rain. Many of the reactions are initiated by sunlight.

    • nitrogen monoxide is formed in high temperature combustion situations e.g. car engines, power station furnace burning coal, oil or natural gas.

      • nitrogen + oxygen ==> nitrogen monoxide

        • N_2(g) + O_2(g) ==> 2NO_(g) 

    • and in air the nitrogen monoxide rapidly combines with the oxygen in air

      • nitrogen monoxide + oxygen ==>  nitrogen dioxide (acidic gas)

        • 2NO_(g) + O_2(g) ==> 2NO_2(g) 

    • The nitrogen dioxide is oxidised to nitric acid by the reaction with oxygen from air when it dissolves in rainwater. The overall process is summarised in the equation below.

      • 4NO_2(g-air) + O_2(g-air) + 2H₂O_(l-rain) ==> 4HNO_3(aq-rain)

  • Carbon monoxide CO, which is toxic, and also involved in the chemistry of 'photochemical smog'. This is formed by inefficient combustion

  • Unburned hydrocarbons, C_xH_y, which can be carcinogenic and are also involved in photochemical smog chemistry.

    • But catalytic converters* can significantly reduced these three unwanted emissions (see above for CO and NO removal, and C_xH_y gets oxidised to CO₂ and H₂O). * e.g. using platinum-rhodium transition metal catalysts, these are dispersed on ceramic bed to give a big surface area for the best reaction rate.

  • There are other indirect pollution problems to do with burning fossil fuels:

  • Lead compounds are added to petrol to improve engine performance. This produces lead compound emissions into the environment. Lead compounds are nerve toxins so it is fortunate they are being phased out in many countries.

  • Photochemical smog is mentioned in the previous paragraph.

• VALUABLE CHEMICAL RESOURCE: Should we using a very valuable source of organic chemicals by merely burning most of it? AND how long will oil reserves last? AND what happens if the oil runs out?

• HYDROGEN - FUEL of the FUTURE?:

  • Hydrogen gas can be used as fuel and a long-term possible alternative to fossil fuels.

  • It burns with a pale blue flame in air reacting with oxygen to be oxidised to form water.

    • hydrogen + oxygen ==> water

    • 2H_2(g) + O_2(g) ==> 2H₂O_(l) 

  • It is a non-polluting clean fuel since the only combustion product is water and so its use would not lead to all environmental problems associated with burning fossil fuels.

    • It is easily distributed in pipes like natural gas, but there are health and safety issues to do with storage and distribution since it is, like natural gas, highly flammable and explosive.

  • It would be ideal if it could be manufactured by electrolysis of water e.g. using solar voltaic-cells or some kind of but the technology is in its infancy.

  • Hydrogen can be used to power fuel cells on the "Extra Electrochemistry" page.

• See also pollution Part 1 Carbon monoxide and Part 2 Plastics.

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