The approximate boiling point of the substance represented by the complete heat curve above is 50 DEGREE CELSIUS.
From the graph given above, it can be seen that when the substance was heated its temperature rises continuously until it gets to the point correspond to line DE. At that point the temperature remain the same over a long period of time before increasing again. It is this point of constancy, that is line DE, that corresponds to the boiling point of the substance.The temperature at this point was constant and was not increasing despite the fact that heat is been added to the substance, this is because, the heat that was been added to the substance was been used to break the chemical bonds in the substance so that state change can occur and the substance can change to gas.
