8: Fuels and Earth Science - YK

Question 1

How are natural gas and crude oil formed?

Answer 1

Ancient remains of microscopic plants and animals that lived in the sea were covered by layers of sediment and put under great pressure, turning them into natural (finite) resources

Question 2

What is crude oil?

Answer 2

A complex mixture of hydrocarbons (as a liquid mixed with solids and gases) that can be extracted from the Earth

Question 3

What is crude oil used for?

Answer 3

• Fractionating into fuels for vehicles, aircraft, ships, heating, and power stations
• Feedstock (raw materials) for petrochemical industry

Question 4

Why is crude oil separated into simpler, more useful mixtures (fractions)?

Answer 4

Crude oil isn’t viscous enough or easy enough to ignite to be a useful fuel

Question 5

What is a fractionating column?

Answer 5

A tall metal tank, which is hottest at the bottom, where vapours rise and cool down, condensing when they reach an area below their boiling point (or exiting through the top), then falling into a tray to be piped away

Question 6

What are the fractions produced in a fractionating column?

Answer 6

Gases: domestic heating + cooking (only gas)
Petrol: fuel for cars
Kerosene: fuel for aircraft
Diesel oil: fuel for some cars and trains
Fuel oil: fuel for large ships and power stations
Bitumen: surfacing roads and roofs (only solid)
(ordered by boiling point, low to high, number of carbon atoms, low to high, ease of ignition, high to low, and viscosity, low to high)

Question 7

What is each fraction in oil?

Answer 7

A mixture of hydrocarbons (not a pure hydrocarbon) with similar number of carbon and hydrogen atoms in their molecules, and similar boiling points

Question 8

What are alkanes and the alkane homologous series?

Answer 8

Most of the compounds in crude oil fractions are alkanes (hydrocarbons with only single covalent bonds - saturated); homologous series is a family of compounds which share some properties (general formula, gradual variation in physical properties like boiling points, chemical properties)

Question 9

What is the order of the alkanes and their general formula?

Answer 9

Methane, ethane, propane, butane, pentane, (hex, hept, oct, non, dec); CnH2n+2

Question 10

What do alkanes form when reacted with excess oxygen?

Answer 10

Carbon dioxide + water

Question 11

What is combustion?

Answer 11

The oxidation reaction when hydrocarbon fuels react with oxygen

Question 12

What is the difference between complete and incomplete combustion?

Answer 12

Complete combustion needs excess oxygen and releases energy and only carbon dioxide and water, incomplete combustion has a limited supply of oxygen and produces less energy and carbon dioxide, water, carbon monoxide, and carbon (smoke and soot)

Question 13

What are some problems with incomplete combustion?

Answer 13

It produces toxic carbon monoxide, the soot produced can block pipes carrying away waste gases from an appliance or blacken buildings or cause breathing problems if it collects in the lungs

Question 14

What is acid rain?

Answer 14

Rain with a pH lower than 5.2 (CO2 makes rainwater naturally acidic)

Question 15

Why is sulfur dioxide a problem with combustion?

Answer 15

Sulfur compounds can occur in hydrocarbon fuels as impurities, which form sulfur dioxide after combustion, sylfur dioxide reacts with water to form sulfurous acid and with oxygen to form sulfuric acid, causing acid rain which can: make soil too acidic for crops, kill fish and insects, stop fish eggs in rivers and lakes from hatching, weather and break down buildings, corrode and weaken metals

Question 16

Why are oxides of nitrogen a problem with combustion?

Answer 16

Car engines (internal combustion engines - mixing air and fuel inside an engine) cause temperatures high enough for nitrogen and oxygen in the air to react together to produce oxides of nitrogen (atmospheric pollutants) which can cause acid rain (nitrogen dioxide forms dilute nitric acid when dissolved in clouds), NO2 is toxic (can cause respiratory diseases like bronchitis), catalytic converters in cars convert most of the oxides to harmless nitrogen

Question 17

What is cracking and why is it done?

Answer 17

Cracking is the breaking down of a larger alkane into a more desirable (higher demand) smaller alkane and alkene (unsaturated hydrocarbon - contains carbon double bond) to be used as fuels or for making polymers by evaporating an oil fraction, passing it over a catalyst containing aluminium oxide, and heating it to about 650 C

Question 18

How has the Earth’s atmosphere changed?

Answer 18

At first, the atmosphere was probably mostly carbon dioxide released by volcanos, with smaller amounts of water vapour and other gases. About 4 billion years ago the Earth cooled down, condensing the water vapour into oceans (CO2 dissolved in water, sea creatures made CaCO3 shells). About 2.4 billion years ago, oxygen was probably released by photosynthesising microorganisms (evidence: iron oxide and microorganism fossils found dating to 2.4 bya).

Question 19

What are the approximate percentages of different gases in the atmosphere today?

Answer 19

Nitrogen - 78%; Oxygen - 21%; Argon - 0.9%; CO2 - 0.04%

Question 20

What are the main greenhouses gases?

Answer 20

Carbon dioxide, methane, water vapour