Physical or Phase changes

[Emily Ngo 1E]

Hi,
I have a clarification question on the difference between physical and phase changes. So the enthalpy of vaporization and enthalpy of fusion would be for phase changes correct? And for changes where the temperature is increasing but there is no change in phase, would we use the equation q=mcΔT to find the heat released? Thank you in advance.

[105691548]

A phase change is a physical change that takes place when matter changes everyday states, but the chemical bonds are not broken or formed. Phase changes occur when substances are melted, frozen, boiled, or sublimated. To answer your question, the enthalpy of vaporization and enthalpy of fusion would be considered as phase change since the matter is changing, and I believe you would use the q=MC△T, to find the heat released if there is no temperature change.

[Cassidy Chiong 2J]

Yes! Enthalpy of vaporization and fusion are only used during phase changes, and q=mcΔT is used when there are no phase changes occurring. I like to think of it as q=mc(ΔT) being used when temperature is changing (i.e. any time there is no phase change since temp. does not change during phase changes).

[Michelle Gong]

Hi Emily!

Just to add on what the others have already said, you will only use the enthalpy of vaporization and fusion when you are doing phase change. As for q=mcΔT, you would do that as you increase the temperature. If you were to search up a heating curve for water, it would be very simple to visualize. Whenever there is a plateau on the graph that is a phase change, and whenever there is a slope, that is when you would be increasing temperature and using q=mcΔT. Furthermore, to comment on the differences between these. You would notice that the phase changes are changes in potential energy and that the q=mcΔT it is change in kinetic energy. Hope this helps!