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A cooling curve is a line graph that represents the change of phase of matter, typically from either a gas to a solid or a liquid to a solid. Time is used in the x-axis while temperature is used for the y-axis. They are often used in chemistry and physics, and can apply to matter behavior during heating, as well as during cooling.[1]
Cooling curve graphs are useful as they clearly show a phenomenon of phase changes of matter. For example, when a sealed container of steam who's temperature begins at approximately 150°C is measured, the temperature of the rapidly cooling gas falls at a rate that is typical of the specific heat capacity of steam. This continues until when it reaches 100°C when the temperature stagnates. After an amount of liquid water has collected the temperature continues to drop, again proportional to the specific heat capacity of water (different from that of steam), until again the temperature stagnates, this time at 0°C. Later, the temperature again resumes falling.
This happens because different phases of matter are associated with different energy levels. Steam at 100°C is the same temperature, but contains much more thermal energy than liquid water at 100°C. The same goes for water and ice at 0°C. This is because molecules of water are much more free to move around as a gas than as a liquid, and that freedom of movement means there is much more kinetic energy associated with each molecule, and that energy is transferred as the substance shifts phase - explaining why energy seemingly disappears when boiling a kettle.
In the part of the curve where temperature decreases, the kinetic energy also decreases while the potential energy stays the same. However, at the phase transition, where the curve is flat, the kinetic energy stays the same while the potential energy decreases.
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