Specific Heat Capacity and Latent Heat Questions - GCSE standard

Q1. An electrical immersion heater supplies heat at a steady rate to 2.5 kg of water at 20°C in a container of thermal capacity 1500 J/K and it is noticed that in 8.0 minutes the temperature of the water rose to 100°C.

After another hour, the water was just boiled away.

(a) Calculate the rate at which energy is supplied by the heater.

(Specific heat capacity of water = 4200 J/kg K)

(4 marks)

(b) What value does this experiment give for the specific latent heat of vaporisation of water?

(2 marks)

(c) The quoted value for the specific latent heat of vaporisation of water is 2.3 x 106 J/kg. Explain why the experimental result value differs from this.

(2 marks)

(Total 8 marks)

Q2. An electric kettle of thermal capacity 820 J/K contains 0.90 kg of water.

If it takes 9.0 min to raise the temperature of the kettle and its contents from 19°C to 100°C, how much longer should it take to boil away half the water?

(Specific heat capacity of water = 4200 J/kg K

Latent heat of vaporisation of water = 2.3 x 106 J/kg)

(5 marks)