Adiabatic Expansion


Moderators: Chem_Mod, Chem_Admin

kshalbi
Posts: 68
Joined: Fri Sep 25, 2015 3:00 am

Adiabatic Expansion

Postby kshalbi » Tue Jan 19, 2016 3:48 pm

If a gas expands adiabatically and you have to find the work it does, do you use the equation for reversible or irreversible reactions?

Chem_Mod
Posts: 19143
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 820 times

Re: Adiabatic Expansion

Postby Chem_Mod » Tue Jan 19, 2016 5:27 pm

No, you would not use the isothermal equations. The work done would be equal to the internal energy change since U=q+w but q=0 for adiabatic. So all you need to know is the initial and final temperatures to find deltaU then that is also w.

kshalbi
Posts: 68
Joined: Fri Sep 25, 2015 3:00 am

Re: Adiabatic Expansion

Postby kshalbi » Tue Jan 19, 2016 9:32 pm

Yeah but then to find w do you use: -PdeltaV or the -nRTln (v1/v2). These two equations are what I meant by the "reversible or irreversible" equations for work.

kshalbi
Posts: 68
Joined: Fri Sep 25, 2015 3:00 am

Re: Adiabatic Expansion

Postby kshalbi » Tue Jan 19, 2016 9:32 pm

Yeah but then to find w do you use: -PdeltaV or the -nRTln (v1/v2). These two equations are what I meant by the "reversible or irreversible" equations for work.

Alan Chien 1J
Posts: 72
Joined: Fri Sep 25, 2015 3:00 am

Re: Adiabatic Expansion

Postby Alan Chien 1J » Tue Jan 19, 2016 9:49 pm

I think what the chem mod is saying is that delta u = q + w. But in an adiabatic expansion q is 0. Therefore U = W. By using a separate equation for U ( change U = 3/2 nRchangeT), you can indirectly solve for W.


Return to “Concepts & Calculations Using First Law of Thermodynamics”

Who is online

Users browsing this forum: No registered users and 2 guests