Register to reply

Free energy change during adsorption

Share this thread:
dikmikkel
#1
May8-13, 06:06 AM
P: 169
Hi,
Suppose I have a dissociative adsorption reaction and want to find the free energy change ΔF, this can be written at constant temperature:
[itex] \Delta F = \Delta E -T\Delta S[/itex]
Now given the adsorption energy [itex] \Delta E_{ads} [/itex] I would like to extrapolate the Free energy assuming that the adsorbate is an ideal gas since I know the experimental entropy.
I Assume that the vibrations from the adsorped moleule does not perturb the substrate vibrations and also that the configurational entropy is not changes(maybe rough):
[itex] \Delta S = S_{ads}-S_{noads}[/itex]
[itex] S_{ads} = S_{subs+a} - S_{subs}-S_{a} = -\Delta S_{vib,gas} -S_{gas}[/itex]
The vibrations term does not need to be extrapolated but the gas term does so:
[itex] S_{gas} = S^{\theta}_{gas} - c_p\log(\dfrac{T}{T^{\theta}}) + k_b\log(\dfrac{p}{p^{\theta}})[/itex]
I feel like i am missing a term of the type [itex]- \dfrac{7}{2}k[/itex] since the translation of the gas is not possible when adsorbed.
Does anyone know if I am right?
Phys.Org News Partner Physics news on Phys.org
Interfaces within materials can be patterned as a means of controlling the properties of composites
A new, tunable device for spintronics
Researchers study gallium to design adjustable electronic components

Register to reply

Related Discussions
Free Energy Change/Equilibirum Biology, Chemistry & Other Homework 10
Thermodynamics - Change in the free energy Introductory Physics Homework 1
Thermodynamics - Change in the free energy Introductory Physics Homework 0
Change in Free Energy in terms of First Law Classical Physics 11
Standard Change in Free Energy Biology, Chemistry & Other Homework 1