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.