Phase Change & Temperature: What's the Difference?

[nothing123]

"When a substance absorbs or releases heat, one of two things can happen: either its temperature changes or it will undergo a phase change but not both at the same time"

Can someone clarify this statement? During a phase change, isn't what's going on really just increasing the kinetic energy of the molecules so intermolecular forces break and thus increasing the temperature of the matter?

Thanks.

 

[Borek]

No. Phase change occurs in one temperature - like ice melting. As long as there is a mixture of ice and water adding heat will melt the ice, but temperature of the mixture remains constant. It is breaking of the forces that kept molecules in solid (liquid) together that consumes the heat.

 

[Blueshift5]

I can clarify this statement for you. When a substance absorbs or releases heat, it can either cause a change in its temperature or a change in its phase, but not both at the same time. This means that when a substance undergoes a phase change, such as melting or boiling, its temperature will remain constant until the phase change is complete. This is because during a phase change, the energy being absorbed or released is being used to break or form intermolecular bonds, rather than increasing the kinetic energy of the molecules. Once the phase change is complete, the temperature will then begin to change again. So, while increasing the kinetic energy of molecules can lead to a change in temperature, it is not the only factor at play during a phase change.