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
Technique simplifies the creation of high-tech crystals
Working group explores the 'frustration' of spin glasses
New analysis of oxide glass structures could guide the forecasting of melt formation in planetary interiors

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