Water and bromine are both simple molecular substances.

a. Both water and bromine form a lattice structure in the solid state. What do you understand by the term lattice?

b. The boiling point of water is 100 °C. The boiling point of bromine is 59 °C. Explain the reason for this difference in terms of intermolecular forces.

c. Use ideas about the kinetic theory to explain what happens when liquid bromine evaporates to form bromine vapour.

d. Some liquid bromine is allowed to evaporate in a closed glass jar until no further change is seen in the colour of the bromine vapour. Under these conditions the vapour pressure is constant.

i What do you understand by the term vapour pressure?

ii Explain why the vapour pressure remains constant in the jar.

e. When 0.20 g of a liquid, Y, with a simple molecular structure was evaporated it produced 80 cm³ of vapour. The temperature was 98 °C and the pressure 1.1 × 10⁵ Pa. Calculate the relative molecular mass of Y.

(R = 8.31 J K^–1 mol^–1)