1. Extended tier only

Compound X is a colourless liquid at room temperature.

A sample of pure X was slowly heated from –5.0 °C, which is below its melting point, to 90 °C, which is above its boiling point. Its temperature is measured every minute and the results are represented on the graph.

i) Complete the equation for the equilibrium present in the region BC.

X (s) $\rightleftharpoons$....................

[1]

ii) What is the significance of temperature t °C?

[1]

iii) What is the physical state of compound X in the region EF?

[1]

iv) What would be the difference in the region BC if an impure sample of X had been used?

[1]