WEBVTT

00:00:00.500 --> 00:00:03.975
Welcome to GCSE Edexcel Science revision.

00:00:04.125 --> 00:00:06.544
Unit C C 16: Fuels.

00:00:09.200 --> 00:00:12.451
A hydrocarbon contains only carbon and hydrogen.

00:00:12.601 --> 00:00:18.614
Methane, C H 4, is a hydrocarbon; ethanol is not, because it also contains oxygen.

00:00:21.267 --> 00:00:27.687
Crude oil is a complex mixture of hydrocarbons with different molecular sizes and chain or ring structures.

00:00:27.837 --> 00:00:31.821
It is not one pure compound and most constituents are not polymers.

00:00:34.500 --> 00:00:40.218
Crude oil supplies fuels and starting materials (feedstock) for the petrochemical industry.

00:00:40.368 --> 00:00:44.476
These are used to make other chemicals and materials, including polymers.

00:00:47.133 --> 00:00:52.934
Crude oil and fossil natural gas are finite, non-renewable resources on human timescales.

00:00:53.084 --> 00:00:57.202
Natural gas is mainly methane and is used in cooking and heating.

00:00:59.867 --> 00:01:04.201
Petrol, kerosene and diesel are fossil fuels obtained from crude oil.

00:01:04.351 --> 00:01:11.505
Hydrocarbons can also be produced by other routes, so not every hydrocarbon molecule is necessarily fossil-derived.

00:01:14.167 --> 00:01:21.653
A fraction is a mixture of hydrocarbons with a similar range of boiling points, not normally a single chemically pure substance.

00:01:24.333 --> 00:01:29.571
Heat crude oil so much of it vaporises, and pass vapour into a fractionating column.

00:01:29.721 --> 00:01:32.558
The column is hot at the bottom and cooler at the top.

00:01:35.233 --> 00:01:40.149
Hydrocarbons condense at different levels according to their boiling points: longer-chain,

00:01:40.299 --> 00:01:43.008
higher-boiling molecules condense lower down;

00:01:43.158 --> 00:01:44.523
shorter-chain,

00:01:44.673 --> 00:01:46.743
lower-boiling ones travel higher.

00:01:49.400 --> 00:01:55.724
Very low-boiling refinery gases can leave the top as gases rather than condensing as liquids there.

00:01:55.874 --> 00:01:59.531
High-boiling residue such as bitumen is collected at the bottom.

00:02:02.200 --> 00:02:05.366
Fractional distillation is a physical separation.

00:02:05.516 --> 00:02:11.787
It does not break carbon chains or change the identity of the hydrocarbons; cracking does that separately.

00:02:14.467 --> 00:02:21.552
The main fractions in order from top towards bottom are gases, petrol, kerosene, diesel oil, fuel oil and bitumen.

00:02:21.702 --> 00:02:26.907
Schematic column; top gases need not condense there and bitumen is bottom residue.

00:02:31.567 --> 00:02:34.447
Gases are used for domestic heating and cooking;

00:02:34.597 --> 00:02:36.111
petrol for cars;

00:02:36.261 --> 00:02:38.075
kerosene for aircraft;

00:02:38.225 --> 00:02:40.358
diesel for some cars and trains;

00:02:40.508 --> 00:02:43.516
fuel oil for large ships and some power stations;

00:02:43.666 --> 00:02:45.693
bitumen for roads and roofs.

00:02:45.843 --> 00:02:49.420
Fractions contain mixtures, not one pure alkane each.

00:02:54.100 --> 00:03:00.872
As chain length generally increases, boiling point and liquid viscosity increase and ease of ignition decreases.

00:03:01.022 --> 00:03:04.593
Larger molecules have stronger intermolecular attractions.

00:03:04.743 --> 00:03:07.963
Compare similar hydrocarbons under the same conditions.

00:03:12.633 --> 00:03:19.256
Viscosity describes resistance to flow: a more viscous liquid flows less readily under comparable conditions.

00:03:19.406 --> 00:03:22.083
Compare temperature as well as composition.

00:03:24.733 --> 00:03:29.948
Alkanes are saturated hydrocarbons: they have only single carbon to carbon bonds.

00:03:30.098 --> 00:03:37.687
Alkanes without rings, called acyclic alkanes, have general formula C subscript n, H subscript two n plus two.

00:03:37.837 --> 00:03:41.661
Ring-shaped hydrocarbons do not necessarily follow this formula.

00:03:44.333 --> 00:03:52.679
The first four alkanes are methane, C H four; ethane, C two H six; propane, C three H eight; and butane, C four H ten.

00:03:52.829 --> 00:03:58.363
Acyclic saturated alkanes follow C subscript n, H subscript two n plus two.

00:04:03.033 --> 00:04:10.519
A homologous series has the same general formula, similar chemical properties and a gradual change in physical properties.

00:04:10.669 --> 00:04:13.293
Neighbouring members differ by C H 2.

00:04:15.967 --> 00:04:23.497
For an acyclic alkane with five carbons, 2n plus 2 equals 12 hydrogen atoms, giving C 5 H 12.

00:04:23.647 --> 00:04:27.281
Check that you are using the correct series before applying the formula.

00:04:29.933 --> 00:04:40.833
Complete combustion with sufficient oxygen produces carbon dioxide and water and releases energy: hydrocarbon plus oxygen produces carbon dioxide plus water.

00:04:43.500 --> 00:04:48.421
For methane: C H 4 plus 2 O 2 produces C O 2 plus 2 H 2 O.

00:04:48.571 --> 00:04:53.786
Balance carbon, hydrogen and oxygen atoms without changing the substance formulae.

00:04:56.467 --> 00:05:07.131
Incomplete combustion occurs with insufficient oxygen and can produce carbon monoxide and or carbon particles (soot), together with water and sometimes carbon dioxide.

00:05:09.800 --> 00:05:17.447
Example C O-producing equation: 2 C H 4 plus 3 O 2 produces 2 C O plus 4 H 2 O.

00:05:17.597 --> 00:05:23.187
A soot-producing example is C H 4 plus O 2 produces C plus 2 H 2 O.

00:05:23.337 --> 00:05:26.481
Real incomplete combustion can produce mixtures.

00:05:26.631 --> 00:05:32.923
Incomplete combustion can yield carbon monoxide and or carbon, rather than one fixed product mix.

00:05:37.600 --> 00:05:46.773
Incomplete combustion releases less useful energy from a given amount of fuel than full oxidation to C O 2, and creates hazards and pollution.

00:05:49.433 --> 00:05:52.790
Carbon monoxide is colourless, odourless and toxic.

00:05:52.940 --> 00:05:57.731
It binds to haemoglobin, reducing the blood's ability to transport oxygen.

00:06:00.400 --> 00:06:07.151
Soot can dirty appliances and obstruct air flow or flues, increasing problems with fuel-burning appliances.

00:06:07.301 --> 00:06:10.383
Carbon particles are also harmful air pollution.

00:06:13.033 --> 00:06:17.705
Complete combustion still releases carbon dioxide, a greenhouse gas.

00:06:17.855 --> 00:06:22.053
Absence of soot does not mean the fuel has no environmental impact.

00:06:24.733 --> 00:06:31.464
Sulfur impurities in some fuels burn to form sulfur dioxide: S plus O 2 produces S O 2.

00:06:31.614 --> 00:06:35.401
Removing sulfur from fuels reduces this source of pollution.

00:06:38.067 --> 00:06:47.239
Sulfur dioxide dissolves in atmospheric moisture to produce acidic solutions; further oxidation can contribute to sulfuric acid formation.

00:06:47.389 --> 00:06:54.225
Do not treat S O 2 plus water alone as directly making H 2 S O 4 without extra oxygen.

00:06:56.900 --> 00:07:04.514
Acid rain can damage plants, acidify lakes and harm aquatic organisms, and react with limestone buildings and monuments.

00:07:07.167 --> 00:07:15.839
An acid-rain carbonate equation is H 2 S O 4 plus C A C O 3 produces C A S O 4 plus H 2 O plus C O 2.

00:07:15.989 --> 00:07:23.816
With a suitable reactive metal: F E plus H 2 S O 4 produces F E S O 4 plus H 2 for dilute acid.

00:07:26.467 --> 00:07:34.177
At high engine temperatures, nitrogen and oxygen from air can react to produce nitrogen oxides, nitrogen oxides.

00:07:34.327 --> 00:07:39.041
Their formation does not require nitrogen to be part of the hydrocarbon fuel.

00:07:39.191 --> 00:07:44.304
Their effects differ: toxic gases, particles, acid rain and greenhouse warming.

00:07:48.967 --> 00:07:53.617
Nitrogen oxides contribute to acidic precipitation and air pollution.

00:07:53.767 --> 00:08:02.800
Catalytic converters reduce several harmful exhaust gases, including converting nitrogen oxides towards nitrogen under suitable conditions.

00:08:05.467 --> 00:08:12.068
Removing sulfur, treating emissions and reducing combustion can help, but different pollutants need different measures.

00:08:12.218 --> 00:08:16.385
C O 2 climate effects differ from S O 2 acid-rain effects.

00:08:19.067 --> 00:08:30.243
Cracking breaks larger saturated hydrocarbon molecules into smaller molecules, including shorter alkanes and unsaturated alkenes, using suitable heating and sometimes catalysts.

00:08:32.900 --> 00:08:40.257
Cracking is useful because demand for short-chain fuels and alkene feedstocks can exceed the supply from simple distillation;

00:08:40.407 --> 00:08:43.913
longer fractions can be converted into more useful products.

00:08:46.567 --> 00:08:51.441
Alkenes are unsaturated hydrocarbons with a carbon to carbon double bond.

00:08:51.591 --> 00:08:59.282
Alkenes without rings and with one C double bonded to C bond have general formula C subscript n, H subscript two n.

00:09:01.933 --> 00:09:08.779
A balanced cracking example is C 10 H 22 produces C 8 H 18 plus C 2 H 4.

00:09:08.929 --> 00:09:12.893
Check totals: ten carbons and twenty-two hydrogens on each side.

00:09:13.043 --> 00:09:17.928
Cracking is chemical change; fractional distillation is physical separation.

00:09:22.600 --> 00:09:28.391
Ethene is a useful feedstock for poly(ethene): monomers join into long-chain molecules.

00:09:28.541 --> 00:09:33.694
Distillation only separates existing molecules; cracking changes them chemically.

00:09:36.367 --> 00:09:40.372
Specific demand and profitability vary by market and time.

00:09:40.522 --> 00:09:44.865
Do not assume petrol is always more profitable than every other fraction.

00:09:47.533 --> 00:09:54.263
Petrol is energy-dense, easy to transport as a liquid and supported by widespread refuelling infrastructure.

00:09:54.413 --> 00:09:58.351
Its combustion emits C O 2 and can produce other pollutants.

00:10:01.033 --> 00:10:07.049
Hydrogen reacts with oxygen to form water: 2 H 2 plus O 2 produces 2 H 2 O.

00:10:07.199 --> 00:10:13.641
The hydrogen fuel itself contains no carbon, so this reaction produces no fuel-derived C O 2.

00:10:16.300 --> 00:10:24.362
Hydrogen is difficult to store and transport compactly and needs suitable tanks or other storage methods and refuelling infrastructure.

00:10:24.512 --> 00:10:27.987
It is flammable and needs appropriate engineering controls.

00:10:30.667 --> 00:10:38.579
Hydrogen production can use fossil feedstocks or electricity, so overall emissions depend on the production method and energy source.

00:10:38.729 --> 00:10:42.375
Tailpipe emissions alone do not describe the full life cycle.

00:10:45.033 --> 00:10:55.934
Burning hydrogen in air at high temperature can form nitrogen oxides; a hydrogen fuel cell operates differently and produces electricity without ordinary combustion.

00:10:56.084 --> 00:11:01.299
No fuel-derived C O 2 at use does not establish zero whole-life emissions.

00:11:05.967 --> 00:11:12.878
Evaluate fuel choices using storage, energy supply, costs, safety and whole-life environmental impacts.

00:11:13.028 --> 00:11:17.470
Avoid saying hydrogen is automatically emission-free in every sense.

00:11:20.133 --> 00:11:21.819
That completes Fuels.

00:11:21.969 --> 00:11:25.314
Revisit the notes and test yourself on the revision website.