## Melting/Evaporation vs Vaporization

Ryan Distaso 3C
Posts: 26
Joined: Fri Sep 25, 2015 3:00 am

### Melting/Evaporation vs Vaporization

When a substance goes from a solid to a gas by vaporization, does it go through the process of melting and then evaporate or does it go directly to a gas?
-Ryan Distaso, Discussion 3E

204643643
Posts: 10
Joined: Wed Nov 18, 2015 3:00 am

### Re: Melting/Evaporation vs Vaporization

My understanding of this concept is that sublimation or "direct vaporization" is the transition from the solid phase to the gas phase, completely skipping the liquid phase.

Kimberly Waszak 2G
Posts: 10
Joined: Fri Sep 25, 2015 3:00 am

### Re: Melting/Evaporation vs Vaporization

The process of a solid transitioning to the gaseous phase is called sublimation. This transition occurs directly, without having to go through the liquid phase.

Samantha Miceli 3J
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Re: Melting/Evaporation vs Vaporization

I think that in order for sublimation to occur, the solid must change to a liquid then a gas. In his lecture notes, Lavelle described the enthalpy of sublimation as Hsub=Hfus+Hvap. This indicates that in the process of sublimation, fusion (solid to liquid) and vaporization (liquid to solid) both occur.

ShangShi1K
Posts: 17
Joined: Fri Sep 25, 2015 3:00 am

### Re: Melting/Evaporation vs Vaporization

Sublimation means a solid turns into a gas directly.
Hsub=Hfus+Hvap does not mean sublimation goes through fusion first and then vaporization or these two processes occur at the same time. It's just a way to calculate the enthalpy of sublimation step by step.
Ex.
Given that
H2O(s)-->H2O(l) Hfus (1)
H2O(l)-->H2O(g) Hvap (2)
When adding the equation (1) and (2)
H2O(s)+H2O(l) -->H2O(l)+H2O(g) which is simplied as H2O(s)-->H2O(g), the process of sublimation, thus Hsub=Hfus+Hvap

- Shang Shi 1K