The temperature-time graph below shows the heating curve for pure wax. From the graph answer the following :
(a) What is the physical state of the substance at the points A, B, C and D ?
(b) What is the melting point of the substance ?
(c ) What is its boiling point ?
(d) Which portions of the graph indicates that change of state is taking place.
(e ) Name the terms used for heat absorbed during change of states involved in above processes.

Explanation

(a) At point A : Wax is in the solid state.
At point B : Wax has started melting and exists both in the solid as well as liquid states.
A point C : Wax is in liquid state.
At point D : Wax has stared boiling. Therefore, it exists both in the liquid as well as gaseous states.
(b) Melting point of wax = `15^(@)C`
(c ) Boiling point of wax `= 110^(@)C`
(d) The change of state (solid to liquid) is represented by the portion `A_(1) " to " B_(2)` (straight line).
The change of state (liquid to gas ) is represented by the portion `D_(1) " to " D_(2)` (straight line).
(e ) It is known as latent heat of fusion in case of solids and latent heat of vaporisation in case of liquids.