Question

The diagram below shows the change of phases of a substance on a temperature vs time graph on heating the substance at a constant rate.

1. Why is the slope of CD less than slope of AB?
2. What is the boiling and melting point of the substance?

Answer 1

(i) The slope of CD is less than that of AB because the specific heat capacity of the liquid is greater than that of the solid. Hence, the temperature of the liquid rises more slowly than that of the solid when heated at a constant rate.

(ii)

• Melting point = \(t_1\) (represented by BC).
• Boiling point = \(t_2\) (represented by DE).