Question
Heat is supplied to one kg of solid material at a constant rate. The temperature of material is changing with heat supplied as shown in the figure below.
(a) What do the horizontal regions AB and CD represent?
(b) If CD = 9AB, then what interpretation can you make?
(c) What does the reciprocal of slope of BC represent?
Solution
(a) The melting of solid is represented by the horizontal portion AB and the magnitude of AB is equal to the latent heat of fusion in kcal/kg.
The horizontal portion CD represents the boiling of liquid and the magnitude of CD is equal to latent heat of vaporisation in k cal/kg.
(b) CD = 9AB implies that the latent heat of vaporisation is nine times the latent heat of fusion.
(c) The curve BC represents the vapour state of substance.
We know,
dQ = msdT
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So, the slope of the graph i.e. 
represents the heat capacity of the liquid.
