A student determined the specific latent heat of vapourisation of water - AQA - GCSE Physics - Question 8 - 2022 - Paper 1

A hazard in the student’s investigation is boiling water, as it poses a risk of burns if proper precautions are not taken.

To find the specific latent heat of vapourisation (L), we first calculate the change in mass (m):

$m = 0.080 ext{ kg} - 0.071 ext{ kg} = 0.009 ext{ kg}$

Next, we use the formula for specific latent heat:
$L = \frac{E}{m}$
where E is the energy supplied (25,200 J).
Substituting the values:

$L = \frac{25,200 ext{ J}}{0.009 ext{ kg}} = 2,800,000 ext{ J/kg}$

Therefore, the specific latent heat of vapourisation of water is 2,800,000 J/kg.

The transfer of thermal energy to the surroundings implies that less energy was available to heat the water itself. As a result, the student would calculate a lower specific latent heat value because the energy used in the calculation does not account for the energy lost, leading to an underestimation of the actual specific latent heat of vapourisation.

If some of the water evaporated before reaching 100 °C, it means that the water was losing mass before the heating process was completed. This would result in a calculated specific latent heat that is too low since the mass used in the calculations would not reflect the actual mass of water that evaporated at the boiling point.