Developing Fuels

Question 1

Why does MTBE produce less carbon monoxide when burnt that pentane

Answer 1

There is less incomplete combustion as the molecule is already partially oxidised

Question 2

Describe how a heterogeneous catalyst works

Answer 2

The reactant is adsorbed to the surface of the catalyst
Intramolecular bonds are weakened and broken
New bonds form
The product diffuses off the surface

Question 3

What’s a structural isomer

Answer 3

a molecule with the same molecular formula but different structural formula

Question 4

What is a biofuel and why is it carbon neutral

Answer 4

Made from crops which can be replanted
Plants take in CO2 for photosynthesis
Which balances out the CO2 produced from burning

Question 5

Explain what is meant by auto-ignition and why it is undesirable in an engine.

Answer 5

Fuel igniting to without a spark which can damage the engine

Question 6

You have a simple methane molecule, what is the shape, the bond angles and why? (5 points)

Answer 6

Tetrahedral
109 degrees
4 areas of negative charge
that repel each other
as far as possible

Question 7

What does octane measure and why is it desirable to increase the number.

Answer 7

Measures the tendency to knock, higher the octane number means less knocking

Question 8

Name 2 products formed by reforming

Answer 8

cycloalkanes and cycloalkenes

Question 9

Explain how the catalyst can be poisoned by lead

Answer 9

The lead stays on the catalyst which prevents other molecules from reaching the surface

Question 10

Suggest a benefit of using hydrogen as fuel

Answer 10

only produces water or does not produce CO2

Question 11

Use ideas of bondmaking and bondbreaking to explain how a reaction can be endothermic

Answer 11

Bond breaking takes in energy, bondmaking gives out energy, here less energy is being given out then taken in

Question 12

Explain what happens in cracking reactions and what types of molecules are produced

Answer 12

a large hydrocarbon is split into shorter alkanes and alkenes

Question 13

Suggest why the use of non-food parts of crop plant is desirable for the production of biofuels

Answer 13

Allows food crops to be used for food

Production of food not affected

Question 14

Give 2 ways in which molecules formed by cracking of a straight chain alkane molecule differ from the original molecule.

Answer 14

Shorter Hydrocarbons

Unsaturated/Alkenes

Question 15

Explain the term catalyst and name the type of catalysis used in cracking

Answer 15

Catalysts speed up a reaction and be recovered unchanged/ not used up
Provide a path of lower activation energy

Heterogeneous catalysis

Question 16

Describe and explain the structural feature of zeolites that make them effective catalysts for the cracking process.

Answer 16

Heterogeneous catalysis occurs on surface (ADSOBED)

Large surface area

Question 17

Name the refining process used to convert straight chain alkanes into branched chain alkenes with the same number of carbon atoms.

Answer 17

Isomerisation

Question 18

One method of disposing of used oil is to burn them. However, this produces atmospheric pollution in the form of a dense black cloud of Carbon particulates
Suggest and explain how these particulates are formed.

Answer 18

Incomplete combustion of oil

Caused by insufficient supply of oxygen

Question 19

What does empirical formula show

Answer 19

It shows the smallest ratio of the different atoms present

Question 20

Is it more desirable have a low or high octane number

Answer 20

High

Question 21

What type of hydrocarbons have high octane numbers

Answer 21

Those with lots of branched chains and aromatic rings and generally shorter

Question 22

What catalysts and conditions are used in isomerisation

Answer 22

Platinum at 260 Celsius and then the products are passed over a zeolite sieve separating the straight from the branched

Question 23

Suggest one reason why the use of non food parts of crops is desirable

Answer 23

Production of food is not effected

Question 24

What pieces of info are needed to workout the enthalpy change of combustion

Answer 24

Mass of fuel
Mr of fuel
Vol of water
Specific heat capacity

Question 25

What are the two products of reforming

Answer 25

Cyclic hydrocarbons and hydrogen

Question 26

What is a structural isomer

Answer 26

Different structural formulae for the same molecular formula