Outline two reasons why oil is one of the world’s significant energy sources.

Formulate an equation for the cracking of C₁₆H₃₄ into two products with eight carbon atoms each.

Identify, giving a reason, which product in (b)(i) could be used in petrol (gasoline).

Outline how higher octane fuels help eliminate “knocking” in engines.

The performance of hydrocarbons as fuels can be improved by catalytic reforming.

Outline how catalytic reforming increases a fuel’s octane rating.

Any two of:

high energy content/high energy density/high specific energy

OR

high enthalpy of combustion/very exothermic enthalpy of combustion

 

shortage of alternatives

OR

alternatives are expensive

OR

oil is relatively cheap

OR

oil is «still» abundant/common

 

well-established technology

OR

easy for consumers to obtain

OR

commonly used

 

easy to store

OR

easy to transport

OR

easy to extract

 

produces energy at a reasonable rate

 

Accept “high potential energy” for M1.

[2 marks]

C₁₆H₃₄(g) → C₈H₁₆(g) + C₈H₁₈(g)

OR

C₁₆H₃₄(g) + H₂(g) → 2 C₈H₁₈(g)

[1 mark]

C₈H₁₈ AND is an alkane

OR

C₈H₁₈ AND petrol does not contain alkenes

 

[1 mark]

fuels can be compressed more without undergoing «unwanted» auto-ignition

 

Accept “burns smoother without undergoing «unwanted» auto-ignition” OR “fuel does not auto-ignite”.

[1 mark]

produces more branched chain hydrocarbons «with higher octane rating»

OR

produces aromatics «which have higher octane rating»

OR

produces cyclohexanes «which have higher octane rating»

 

 

Accept “increase branches”.

Do not accept “produces benzene”.

Do not penalize for “benzene” if penalty applied in 2.b.iii.

Accept “produces cyclic structures”.

[1 mark]

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