This question is about internal energy.

(i) Mathilde raises the temperature of water in an electric kettle to boiling point. Once the water is boiling steadily, she measures the change in the mass of the kettle and its contents over a period of time.

The following data are available.

Initial mass of kettle and water = 1.880 kg
Final mass of kettle and water = 1.580 kg
Time between mass measurements = 300 s
Power dissipation in the kettle = 2.5 kW

Determine the specific latent heat of vaporization of water.

(ii) Outline why your answer to (b)(i) is an overestimate of the specific latent heat of vaporization of water.

(i) mass lost in 300 s=(1.880-1.580)=0.3 (kg);
(energy supplied=750 kJ) (do not award credit for this line)
L=2.5 MJ kg^–1; (unit must appear correctly here)
Award [2] for a bald correct answer.

(ii) energy will be transferred to surroundings; } (accept energy is lost by/from kettle to surroundings)
so calculated energy to water is too large / change in mass too large;
(hence overestimate)
Award [0] for a bald correct answer.
Treat references to energy gained by kettle as neutral; the kettle is at a constant temperature.