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.

The temperature-time graph below shows the heating curve for pure wax.

1.	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.
Answer» Solution :(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.