4.7.1Carbon Compounds as fuels and feedstock

Question 1

Crude oil

Answer 1

is a finite resource which is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.

crude oil is a mixture of a very large number of compounds, most of which are hydrocarbons

most of the hydrocarbons in crude oil are alkanes

Question 2

Fractional distillation

Answer 2

Crude oil is heated until most of it vaporises
The mixture of vapours and liquid enters the fractionating column
Temperature gradient: hot at bottom, cold at top
Vapours rise up the column
Large hydrocarbons have high boiling points so they condense early on and drain out near the bottom of the column. They have high boiling points because they have strong intermolecular forces so lots of energy is needed to overcome these forces.
Small hydrocarbons have low boiling points so they condense near the top of the column where it is cooler. They have low boiling points because they have weaker inter molecular forces—less energy required to overcome these forces.
This separates the oil into fractions. Each fraction contains a mixture of hydrocarbons with similar boiling points (around same number of C atoms) Each fraction is collected.

Question 3

Small hydrocarbons vs large hydrocarbons

Answer 3

Small:
Low bp
High flammability
Clean flame
Runny (viscosity)

Large:
High bp
Low flammability
Dirty flame
Viscous

Question 4

Uses of crude oil fractions

Answer 4

Fuels, e.g. liquefied petroleum gases, petrol, kerosine (aeroplanes), diesel, heavy fuel oil (ships and heating)

Other fractions are used as feedstock for processes to make useful substances e.g. medicine, detergents, solvents, lubricants and polymers (plastics)

Question 5

Combustion
Problems with combustion

Answer 5

Complete:
Fuel + oxygen -> CO2 + H2O
Incomplete:
Fuel + oxygen -> CO + water
Fuel + oxygen ->carbon (soot) + H2O

Global warming, acid rain, global dimming
Sulphur is often contained as an impurity in hydrocarbons

Question 6

Carbon dioxide how is it formed

Answer 6

Complete combustion of any fuel containing carbon atoms

Question 7

Carbon monoxide how is it formed

Answer 7

Incomplete combustion of any fuel containing carbon atoms

Question 8

Sulphur Dioxide how is it formed

Answer 8

Combustion of a fossil fuel which contains sulphur impurities

Question 9

Nitrogen oxides how is it formed

Answer 9

Oxidation of atmospheric nitrogen inside the engine of a car, lorry, etc

Question 10

Unburned hydrocarbons how is it formed

Answer 10

Hydrocarbon fuel molecules which have not been oxidised at all

Question 11

Particulates how is it formed

Answer 11

Incomplete combustion of any fuel containing carbon atoms

Question 12

Carbon dioxide potential problems

Answer 12

Causes global warming

Question 13

Carbon monoxide potential problems

Answer 13

Toxic

Question 14

Sulphur dioxide potential problems

Answer 14

Acid rain

Question 15

Nitrogen oxides potential problems

Answer 15

Acid rain

Question 16

Unburned hydrocarbons potential problems

Answer 16

Toxic

Question 17

Particulates potential problems

Answer 17

Global dimming

Question 18

Cracking

Answer 18

The process of breaking sown large hydrocarbons molecules into smaller ones by heating them in the presence of a catalyst
It helps match the supply of fractions with the demand for them
It produces alkenes which are useful as feed stock for the petrochemical industry
Thermal decomposition reaction

Catalytic:
Slight pressure just above atmospheric pressure (high temperature, 550C) and in the presence of a zeolite catalyst

Steam:
Very high temperatures—around 800C, no catalyst, in the presence of steam

Question 19

Alkanes vs alkenes

Answer 19

Alkanes:
Saturated
CnH2n+2
Uses - fuel
No colour change with bromine water

Alkenes:
Unsaturated
CnH2n
Uses - to make polymers
Change to colourless from orange with bromine water