Phase changes with entropy?

Moderators: Chem_Mod, Chem_Admin

Fenared Ortiz 3K
Posts: 37
Joined: Wed Nov 16, 2016 3:03 am

Phase changes with entropy?

Postby Fenared Ortiz 3K » Thu Feb 08, 2018 9:20 am

Do we still have to account for phase changes when trying to find the entropy of the system? If so how would we approach doing so.

Sara Varadharajulu
Posts: 60
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 1 time

Re: Phase changes with entropy?

Postby Sara Varadharajulu » Thu Feb 08, 2018 10:48 am

yes, you do. the entropy increases when going from solid to liquid to gas and decreases in the opposite direction. you can use delta s= q(rev)/T. the q for a reversible reaction is equal to the enthalpy of fusion, vaporization etc. this will help you account for the entropy change during phase changes.

Sally Nason - 1K
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

Re: Phase changes with entropy?

Postby Sally Nason - 1K » Thu Feb 08, 2018 10:52 am

During a phase change, the temperature does not change but heat must still go into/leave the system in order to cause the phase change. Since heat is entering or leaving the system, the entropy will change and therefore needs to be accounted for.

JennyCKim1J
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

Re: Phase changes with entropy?

Postby JennyCKim1J » Thu Feb 08, 2018 11:43 am

So both enthalpy and entropy change during phase changes?

Lily Sperling 1E
Posts: 49
Joined: Tue Oct 10, 2017 7:14 am

Re: Phase changes with entropy?

Postby Lily Sperling 1E » Thu Feb 08, 2018 1:11 pm

Yes, both enthalpy and entropy change during a phase change, but keep in mind when simply asked is the reaction spontaneous at a given temp, you do not account for entropy or enthalpy change to get to that temp, but are only looking at the spontaneity of the phase change itself.

CalebBurns3L
Posts: 47
Joined: Fri Sep 29, 2017 7:07 am

Re: Phase changes with entropy?

Postby CalebBurns3L » Fri Feb 09, 2018 2:30 am

Both the entropy and enthalpy change during a phase change, so yes.

Guadalupe T 1E
Posts: 58
Joined: Fri Sep 29, 2017 7:04 am

Re: Phase changes with entropy?

Postby Guadalupe T 1E » Mon Feb 12, 2018 11:27 pm

You can also use the equation deltaS= n x delta H / T when there is vaporization/ fusion and deltaS= nCpln(T2/T1) for phase changes.


Return to “Phase Changes & Related Calculations”

Who is online

Users browsing this forum: No registered users and 2 guests