Fuels and Earth Science

Question 1

What are hydrocarbons?

Answer 1

Hydrocarbons are compounds that contain carbon and hydrogen only.

Question 2

What is crude oi?

Answer 2

-A complex mixture of hydrocarbons.
-Containing molecules in which carbon atoms are in chains or rings (names, formulae and structures of specific ring molecules not required)
-An important source of useful substances (fuels and feedstock for the petrochemical industry).
- A finite resource

Question 3

Describe the separation of crude oil into simpler, more useful mixtures by the process of fractional distillation

Answer 3

-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.

Question 4

What are the names and uses of the fractions?

Answer 4

-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

Question 5

How hydrocarbons in different fractions differ from each other?

Answer 5

-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.

Question 6

What does it mean if compounds are part of the homologous series?

Answer 6

-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.

Question 7

Describe the complete combustion of hydrocarbon fuels as a reaction

Answer 7

-CO2 and H2O are produced.
-Energy is given out (exothermic).

Question 8

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

Answer 8

-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.

Question 9

How does carbon monoxide behave as a toxic gas?

Answer 9

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.

Question 10

Describe the problems caused by incomplete combustion producing carbon monoxide and soot in appliances that use carbon compounds as fuels

Answer 10

-Carbon monoxide causes health problems.
-Soot causes global dimming.

Question 11

How do impurities in some hydrocarbon fuels result in the production of sulfur dioxide?

Answer 11

-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.

Question 12

What are some problems associated with acid rain caused when sulfur dioxide dissolves in rain water?

Answer 12

-Damages buildings and statues (made of limestone).
-Reduce the growth of or kill trees and crops.
-Lower pH of water in lakes, killing fish.

Question 13

Why when fuels are burned in engines, oxygen and nitrogen can react together at high temperatures to produce oxides of nitrogen, which are pollutants?

Answer 13

-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.

Question 14

What are the advantages and disadvantages of using hydrogen, rather than petrol, as a fuel in cars?

Answer 14

-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

Question 15

Petrol, kerosene and diesel oil are…

Answer 15

Non-renewable fossil fuels obtained from crude oil.
And methane is a non-renewable fossil fuel found in natural gas.

Question 16

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

Answer 16

-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 have the general formula CnH2n
○ The first 2 alkenes are ethene and propene.
○ They are unsaturated because they have a double bonds.

Question 17

Why is cracking is necessary?

Answer 17

-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.

Question 18

What are the gases that were produced by volcanic activity which formed the Earth’s early atmosphere?

Answer 18

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.

Question 19

What was the early earth atmosphere thought to contain?

Answer 19

Little or no oxygen
A large amount of CO2
Water vapour
Small amounts of other gases

Question 20

How does condensation of water vapour form oceans?

Answer 20

Water vapour condensed to form the oceans – H2O (g) -> H2O (l)

Question 21

How did the amount of CO2 in the atmosphere decrease when CO2 dissolved as the oceans formed?

Answer 21

CO2 dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of CO2 in the atmosphere.

Question 22

Explain how the growth of primitive plants consequently led to the increase of O2 in the atmosphere?

Answer 22

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.

Question 23

What is the chemical test for oxygen?

Answer 23

Uses a glowing splint inserted into a test tube of the gas, splint relights if oxygen is present.

Question 24

Describe the Green house effect

Answer 24

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.

Question 25

Describe the effects to Climate Change

Answer 25

Activities increase levels of CO2 & CH4:

Driving (CO2 )
Consuming electricity (CO2 )
Raising livestock (cows – CH4 )
Decay of organic waste in landfill sites (CH4 )
As the temperature increases, it causes coral to push out photosynthetic algae that live in their tissues. These algae provide the colour of coral, and so bleaching occurs.