Observe the following graph and answer the following questions :[Graph: temperature in ºC on the y-axis (0 to 100) against time in minutes on the x-axis (0 to 34). From A (0 ºC, 0 min) the line runs horizontally along 0 ºC to B (about 5 min), marked…

Answer: (a) The graph shows the change in temperature of ice/water with time when heat is supplied continuously (heating curve of water); (b) AB represents the melting of ice at a constant temperature of 0 ºC (ice + water); (c) BC represents the rise in temperature of water from 0 ºC to 100 ºC (liquid state).

(a) The graph shows how the temperature of a given mass of ice changes with time as heat is supplied continuously — ice melts into water, the water gets heated and finally boils and changes into vapour.

(b) Along AB the line is horizontal at 0 ºC: although heat is being supplied, the temperature does not rise. This heat is used as the latent heat of fusion to convert ice at 0 ºC into water at 0 ºC, so ice and water (solid + liquid) are present together. AB represents the melting of ice (melting point of ice = 0 ºC).

(c) Along BC all the ice has melted and the temperature of the water rises steadily from 0 ºC to 100 ºC; the water is in the liquid state. (After C, along CD, the temperature remains constant at 100 ºC while water boils and changes into vapour — latent heat of vaporisation.)