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A Level Specific Heat Capacity Questions

Q11.

(a) Calculate the energy released when 1.5 kg of water at 18 °C cools to 0 °C and then freezes to form ice, also at 0 °C.

specific heat capacity of water = 4200 J kg-1 K-1

specific latent heat of fusion of ice = 3.4 × 105 J kg-1

(4 marks)

Water cooling to zero

ΔQ = mcΔθ

ΔQ 1= 1.5 × 4200 × 18

ΔQ 1= 1.1 × 105 (J)

Ice forming

Δ Q2 = 1.5 × 3.4 × 105 = 5.1 × 105 (J)

---------------------------

total energy released = 1.1 × 105 + 5.1 × 105

total energy released = 6.2 × 105 J

(b) Explain why it is more effective to cool cans of drinks by placing them in a bucket full of melting ice rather than in a bucket of water at an initial temperature of 0 °C.

Ice requires an input of latent heat energy to melt. The ice therefore takes this energy from the drink until it has all melted. This cools the cans before a heat exchange between the drink and melted ice begins. Water at 0 ºC would exchange heat with the cans but only cool them to an intermediate temperature - the ice would cool them to almost zero degrees.

(2 marks)

(Total 6 marks)