Topic 8 - FUELS

What are hydrocarbons

compounds that contain carbon and hydrogen only

What is 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

what process do you use to separate fractional distillation

fractional distillation

explain how you separate crude oil

• crude oil is heated in a furnace where most of the hydrocarbons evaporate

• Vapour rises up the distillation column, cooling as they rise

• when they have cooled to their b/p they condense into liquids

• short chain hydrocarbons have low b/p so they rise to the top , cooler part of the column

• B/P of alkane increases as the n.o C atoms increases

What are the fractions and their uses?

1) Gases - used in domestic heating and cooking

2) Petrol - used as fuel for cars

3) Kerosene - used as fuel for aircraft

4) diesel oil - used as fuel for some cars and trains

5) fuel oil - used as fuel for large ships in some power stations

6) Bitumen - used to surface roads and roof

Explain how hydrocarbons in different fractions differ from each

other in:

a the number of carbon and hydrogen atoms their molecules

contain

b boiling points

c ease of ignition

d viscosity

and are mostly members of the alkane homologous series

• Volatility and ease of ignition decreases as you go down the fractions

• chain length, viscosity and boiling point increases as you go down the fraction

What is the homologous series

a series 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 as a

reaction in which:

• carbon dioxide and water are produced

• energy is given out

Explain why the incomplete combustion of hydrocarbons can

produce carbon and carbon monoxide

because there is a limited supply of oxygen

pruduce carbon and carbon monoxide

Explain how carbon monoxide behaves as a toxic gas

• odourless, colourless, toxic gas

• Binds to haemoglobin in red blood cells

• → reducing the blood capacity to carry oxygen through body cells

Describe the problems caused by incomplete combustion

producing carbon monoxide and soot in appliances that use

carbon compounds as fuels

soot can cause you to have breathing problems if it is inhaled because it goes to your lungs - it is what makes appliance flames smokey

Carbon monoxide can bind to your haemoglobin in your red blood cells reducing the blood capacity to carry oxygen to body cells

• can make you lose consciousness,struggle of breathing , death

Explain how impurities in some hydrocarbon fuels result in the

production of sulfur dioxide

hydrocarbon fuels may contain sulfur compounds as impurities. when the hydrogen fuel is burnt, the sulfur reacts with oxygen to form sulfur dioxide gas (SO2)

what happens when sulphur dioxide dissolves in rain water

• causes acid rain

• → acid rain leaches minerals from soils so plants cant grow and prevents fish eggs from heating in rivers / lakes

• INcreases the rate of weathering of limestone

8.13 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

car engines are 'internal combustion engines' - fuel is mixed with air and ignited inside the engine. this causes temperatures high enough for nitrogen and oxygen inside the engine to react together. produse various oxides of nitrogen (NOx) which are pollutants

Evaluate the advantages and disadvantages of using hydrogen,

rather than petrol, as a fuel in cars

Advantages:

It releases more energy per kilogram than any other fuel (except for nuclear fuels)

It does not pollute as it only produces water on combustion, no other product is formed

Disadvantages:

Expensive to produce and requires energy for the production process

Difficult and dangerous to store and move around (usually stored as liquid hydrogen in highly pressurised containers)

The production of hydrogen process releases carbon dioxide

what type of fossil fuel is petrol,kerosene and diesel oil and how are they obtained

non renewable and obtained from crude oil

hat type of fossil fuel is mathane and how is it obtained

non renewable and from natural ggas

what does cracking involve

involves the breaking down of larger,

saturated hydrocarbon molecules (alkanes) into smaller, more

useful ones, some of which are unsaturated (alkenes)

why is cracking necessary

matches supply with demand

so that the more valuable hydrocarbons can be made