The graph shown in the figure represents change in the temperature of 5kg of a substance with time, as it absorbs heat at a constant rate of 42kJmin−1. The latent heat of vapourization of the substance is:
A
630kJkg−1
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B
126kJkg−1
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C
84kJkg−1
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D
12.6kJkg−1
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Solution
The correct option is C84kJkg−1
AB represents liquid to vapour phase change which occurs for 10min and in each minute 42kJ of heat is supplied. Thus, △Q=42×10=420kJ
This heat vapourises 5kg of the substance. 5Lv=420Lv=84kJkg−1 .