DP Chemistry (last assessment 2024)

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Question 18M.3.sl.TZ2.b

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Date May 2018 Marks available [Maximum mark: 2] Reference code 18M.3.sl.TZ2.b
Level sl Paper 3 Time zone TZ2
Command term State, Suggest Question number b Adapted from N/A
b.
[Maximum mark: 2]
18M.3.sl.TZ2.b

The process of converting heat to electricity is limited by its thermal (Carnot) efficiency.

Thermal efficiency = temp. of steam at source (K)  −  temp. heat sink (K) temp. of steam at source (K) × 100

Power plants generating electricity by burning coal to boil water operate at approximately 35% efficiency.

State what this means and suggest why it is lower than the thermal efficiency.

[2]

Markscheme

35% of chemical/potential energy available in coal is transformed to electricity/electrical energy

 

not all chemical energy from burning fuel transferred into heating water

OR

energy dispersed elsewhere/energy lost due to friction of moving parts

OR

heat loss to the surroundings

 

Accept “stored energy” for “potential energy”.

[2 marks]

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