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On page 17 of the course reader, it says that the temperature of a sample remains constant even though heat is being supplied for melting and boiling phase changes. I'm a little confused on how the temperature remains constant, what's the explanation behind that?
The temperature remains constant even though heat is being supplied because of where the temperature being applied goes to. At the temperature of the phase change, the heat added to the system goes into breaking the bonds, therefore allowing a phase change to happen. Due to this heat being used for breaking bonds, it does not have any affect in increasing the temperature of the system as a whole as it is being used up as energy.
The temperature remains constant during a phase change because the heat is being used to break the bonds, not raise the temperature. This is why on a temperature curve, you can tell a phase change is happening when the line plateaus.
Usually the constant controlled temperature of the system can be explained by the setup of the experiment, which is not always mentioned. For example, Dr. Lavelle mentioned an experiment that could occur underwater in water of a uniform temperature, or in a closed system such as a calorimeter.
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