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Question 18N.3.sl.TZ0.10

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Date November 2018 Marks available [Maximum mark: 5] Reference code 18N.3.sl.TZ0.10
Level sl Paper 3 Time zone TZ0
Command term Calculate, Comment, Formulate Question number 10 Adapted from N/A
10.
[Maximum mark: 5]
18N.3.sl.TZ0.10

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

(a)

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

[1]

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)”.

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

(b.i)

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

[1]

Markscheme

« 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.ii)

Comment on the specific energies of hydrogen and methane.

[1]

Markscheme

« 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»”.

(c)

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]

Markscheme

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.

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