Decide whether each of these statements is True (T) or False
The specific heat capacity of water is 4200 J kg-1 K-1 and the specific latent heat of vaporisation of water at
100ºC is 335 kJ/kg.
(i) It takes more heat to vaporise 1 kg of water at 100ºC than to heat it from 0ºC to 100ºC.
(ii) To take 1 kg of water from liquid at 0ºC to vapour at 100ºC requires 339.2 kJ.
A) (i) T (ii) T
B) (i) T (ii) F
C) (i) F (ii) T
D) (i) F (ii) F

Question

Quizplus · Accepted Answer

(i) is true because the specific latent heat of vaporisation of water is higher than the specific heat capacity of water, meaning that it takes more heat to vaporize 1 kg of water at 100ºC than to heat it from 0ºC to 100ºC.

(ii) is false because to take 1 kg of water from liquid at 0ºC to vapour at 100ºC requires more than just the specific latent heat of vaporisation. You also need to heat the water from 0ºC to 100ºC, which requires the specific heat capacity of water. The correct amount of energy required is:

(1 kg) x (4200 J/kg ºC) x (100ºC) + (1 kg) x (335 kJ/kg) = 419.2 kJ + 335 kJ = 754.2 kJ

Therefore, statement (ii) is false.

Decide Whether Each of These Statements Is True (T) or False