1.1. The energy required to boil water at 100 °C to steam at 100 °C is must greater than the energy required to melt ice at 0 °C to water at 0 °C. 

Explain this, in terms of the spacing of the molecules.

1.2. A heater supplies energy at a constant rate to 64 g of a substance. The variation with time of the temperature of the substance is shown in Fig. 1.1. The substance is perfectly insulated from its surroundings.

Fig 1.1

The power of the heater is 230 W. 

Use data from Fig. 1.1 to calculate, in MJ kg^–1, the specific latent heat of vaporisation, L of the substance.

1.3. Calculate the ratio  $\frac{specificlatentheatofvaporisation}{specificlatentheatoffusion}$.

1.4. Suggest what can be deduced from the fact that section X on the graph is steeper than section Y in Fig 1.1.