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Date November 2018 Marks available 1 Reference code 18N.3.sl.TZ0.10
Level SL Paper 3 Time zone TZ0
Command term Calculate Question number 10 Adapted from N/A

Question

Coal can be converted to clean-burning synthetic natural gas.

Automobile companies use hydrogen as an alternative to fossil fuels. Some properties of fuels are shown.

Formulate equation(s) for the conversion of coal and steam to methane.

[1]
a.

Calculate the specific energy, in kJ g−1, of methane.

[1]
b.i.

Comment on the specific energies of hydrogen and methane.

[1]
b.ii.

Calculate the mass, in kg, of carbon dioxide produced by the complete combustion of 72.0 dm3 octane, C8H18.

Density of C8H18 = 703 g dm−3

C8H18 (l) + 12.5O2 (g) → 8CO2 (g) + 9H2O (g)

[2]
c.

Markscheme

ALTERNATIVE 1:

2C (s) + 2H2O (g) → CH4 (g) + CO2 (g) ✔

 

ALTERNATIVE 2:

C (s) + 2H2O (g) → CO (g) + H2 (g) AND 3H2 (g) + CO (g) → CH4 (g) + H2O (g) ✔

 

Accept “3C (s) + 2H2O (g) → CH4 (g) + 2CO (g)”.

a.

« 891 kJ mo l 1 16.05 g mo l 1 =» 55.5 «kJ g–1» ✔

 

Do not penalize negative sign.

Do not accept energy density at STP/density at STP = 39.3 0.707  = 55.06 «kJ g–1».

b.i.

« 141.6 55.5 » hydrogen/H2 produces 2.6 times/more than twice the energy of methane/CH4 «per mass/g»

OR

less mass of hydrogen/H2 required «to produce same amount of energy»

OR

hydrogen/H2 more energy efficient ✔

 

Accept “hydrogen/H2 produces «nearly» three times more energy than methane/CH4 «per mass/g»”.

b.ii.

moctane «= 72.0 dm3 × 703 g dm–3» = 50600 «g»/50.6 «kg» ✔

mcarbon dioxide «= 8 × 44.01 114.26 × 50.6 » = 156 «kg» ✔

 

Award [2] for correct final answer.

c.

Examiners report

[N/A]
a.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
c.

Syllabus sections

Options » C: Energy » C.1 Energy sources
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