Melting/Evaporation vs Vaporization

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

Melting/Evaporation vs Vaporization

Postby Ryan Distaso 3C » Sun Jan 10, 2016 2:47 pm

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

Postby 204643643 » Sun Jan 10, 2016 3:00 pm

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
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Joined: Fri Sep 25, 2015 3:00 am

Re: Melting/Evaporation vs Vaporization

Postby Kimberly Waszak 2G » Sun Jan 10, 2016 3:03 pm

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
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Joined: Fri Sep 25, 2015 3:00 am

Re: Melting/Evaporation vs Vaporization

Postby Samantha Miceli 3J » Sun Jan 10, 2016 3:13 pm

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

Postby ShangShi1K » Sun Jan 10, 2016 3:46 pm

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


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