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Specific Heat Capacity and Latent Heat Questions - GCSE standard

Q8. The diagram shows water being heated. Eventually the water changed into steam.

(a)

(i) How does the average distance between the particles in steam differ from the average distance between the particles in liquid water?

The steam particles are on average further apart than the liquid water particles.

(ii) How does the density of steam compare to the density of liquid water?

The steam is less dense than the water.

[2 marks]

(b) The sketch-graph shows how the temperature of the water varied with time.

What is the name of the process that is taking place between points A and B? Give a reason for your answer.

The process is the boiling of the water. The temperature remains constant as the particles use the energy they gain to change state rather than get hotter.

[2 marks]

(c) A mass of 63 g of water was turned into steam. The specific latent heat of vaporisation of water is 2.26 MJ/kg

Calculate the thermal energy transferred to the water to turn it into steam.

63g = 0.063 kg

ΔQ = ml

ΔQ = 0.063 x 2.26

ΔQ = 0.14 MJ

ΔQ = 140 kJ would also get you the marks as would ΔQ = 140,000 J

The answer should be given to 2 significant figures as the mass was only given to 2 sig figs - but you were not penalised for this at this level.

[4 marks]

(d) The mass of the steam was 0.063 kg. The volume of the steam was 0.105 m3

Calculate the density of steam.

Density = mass/volume

ρ = m/V 

ρ = 0.063/0.105

ρ = 0.60 kg m-3 (or 0.60 kg/m3)

The answer should be given to 2 significant figures as the mass (the quantity given to the fewest sig figs) was given to 2 sig figs - but you were not penalised for not doing this at this level and got the mark if you put 0.6 rather than 0.60.

[3 marks]

(Total 11 marks)