DP Chemistry (last assessment 2024)

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Question 19N.3.sl.TZ0.11

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Date November 2019 Marks available [Maximum mark: 5] Reference code 19N.3.sl.TZ0.11
Level sl Paper 3 Time zone TZ0
Command term Calculate, Discuss Question number 11 Adapted from N/A
11.
[Maximum mark: 5]
19N.3.sl.TZ0.11

Consider the following data for butane and pentane at STP.

(a)

Discuss the data.

[3]

Markscheme

«similar specific energy and» pentane has «much» larger energy density ✔

Any two for [2 max]:
similar number of bonds/«C and H» atoms in 1 kg «leading to similar specific energy» 
OR
 only one carbon difference in structure «leading to similar specific energy» ✔
NOTE: Accept “both are alkanes” for M2.

pentane is a liquid AND butane is a gas «at STP» ✔
NOTE: Accept “pentane would be easier to transport”.

1 m3 of pentane contains greater amount/mass than 1 m3 of butane ✔
NOTE: Accept “same volume” for “1 m3” and “more moles” for “greater amount” for M4.

(b)

In a natural gas power station, 1.00 tonne of natural gas produces 2.41 × 104 MJ of electricity.

Calculate the percentage efficiency of the power station.

1 tonne = 1000 kg
Specific energy of natural gas used = 55.4 MJ kg−1

[2]

Markscheme

«energy input =» 5.54 ×104 «MJ» ✔
«efficiency = 2.41×104 MJ5.54×104 MJ×100=» 43.5 «%» ✔

NOTE: Award [2] for correct final answer.

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