A Level Specific Heat Capacity Questions
Q5.A tray containing 0.20 kg of water at 20 °C is placed in a freezer.
(a) The temperature of the water drops to 0 °C in 10 minutes.
(specific heat capacity of water = 4200 J kg - 1 K – 1)
Calculate
(i) the energy lost by the water as it cools to 0 °C,
ΔQ = mcΔθ
energy lost by water = 0.20 × 4200 × 20 
= 1.7 × 104 J [1.68 x 104 J]
(ii) the average rate at which the water is losing energy, in J s–1.
rate of loss of energy = (1.68 x 104)/(10 x 60) = 28W
(3 marks)
(b)
(i) Estimate the time taken for the water at 0 °C to turn completely into ice.
(specific latent heat of fusion of water = 3.3 x 1 0 5 J kg – 1)
ΔQ = ml = Pt
28 × t = 0.20 × 3.3 × 105
t = 2.4 × 103 s (2.36 × 103 s)
(ii) State any assumptions you make.
That there is a constant rate of heat loss
That the ice remains at 0oC
(3 marks MAX)
(Total 6 marks)
About this site
