Identify an element, other than carbon and hydrogen, found at significant concentrations in fossil fuels.

Petroleum contains many hydrocarbons. Explain how these are separated by fractional distillation.

Determine the specific energy and energy density of petrol (gasoline), using data from sections 1 and 13 of the data booklet. Assume petrol is pure octane, C₈H₁₈. Octane: molar mass = 114.26 g mol⁻¹, density = 0.703 g cm⁻³.

Outline why the energy available from an engine will be less than these theoretical values.

nitrogen/N

OR

oxygen/O

OR

sulfur/S

Accept “phosphorus/P”.

[1 mark]

Any three of:

different molar masses

OR

different strengths of intermolecular forces

different boiling points

temperature in «fractionating» column decreases upwards

«components» condense at different temperatures/heights

OR

«component with» lower boiling point leaves column first

[3 marks]

specific energy «= \(\frac{{{\text{energy released}}}}{{{\text{mass consumed}}}}\) = \(\frac{{5470{\text{ kJ mo}}{{\text{l}}^{ - 1}}}}{{114.26{\text{ g mo}}{{\text{l}}^{ - 1}}}}\)» = 47.9 «kJ g^–1»

energy density «\(\frac{{{\text{energy released}}}}{{{\text{volume consumed}}}}\) = specific energy × density = 47.9 kJ g^–1 × 0.703 g cm^–3» = 33.7 «kJ cm^–3 »

Do not accept “–47.9 «kJ g^–1»”.

Do not accept “–33.7 «kJ cm^–3»” unless “–47.9 «kJ g^–1»” already penalized.

[2 marks]

energy is lost «to the surroundings» as heat/sound/friction

OR

energy is lost to the surroundings «as heat/sound/friction»

OR

incomplete combustion

Do not accept just “energy is lost”.

[1 mark]