The heating curve is a graph of temperature versus the amount of heat added. The heating curve shows the changes in temperature that result as the substance absorbs an increasing amount of heat. We can also observe that the temperature remains constant while the change of state is in progress. The temperature plateaus because all the heat energy is used to break the intermolecular forces.

The graph shows heat added on the X-axis and temperature in degrees Celsius on the Y-axis for water. From -50 degrees Celsius until 0 degrees Celsius, when heat is added, temperature increases linearly. At 0 degrees Celsius, the temperature doesn't increase with more heat added. After a certain amount of heat is added, the temperature increases linearly again until it reaches 100 degrees Celsius. At 100 degrees Celsius, the temperature does not increase with the heat added. More heat is added at 100 degrees Celsius compared to 0 degrees Celsius before the temperature starts increasing again. After this phase is over, the temperature increases linearly again with the heat added up to 125 degrees Celsius.

Figure 1. Heating curve of water at a constant pressure of 1 atm. 1: Ice is heating towards the melting point; 2: The ice is melting. H2O(s) --> H2O(l) ; 5: The steam is heating to certain temperature.

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