1 reply to this topic

[guiromero]

Hello,

I have a doubt in a question from a chemistry MIT course:

 

"Assume that a material has an activation energy for substitutional self diffusion migration energy of 250 kJ/mol and a Do prefactor of 100 mmm2/s. Calculate the following quantities for this material (express all your answers in units of mm2/s):

 

a) Calculate the vacancy diffusion coefficient at 750°C"

 

______________________________________________________________________________________

My attempt is attached. The formula given in the lecture is D = Do * exp(-Ea + Delta Gn)/RT
However, they don't explain what Delta Gn is, I suppose it is Gibbs free energy, but as the statement doesn't give any other extra energy value despite of the activation energy (Ea), I didn't include Gn in the equation.

The correct answer is: 5.5e-8 mm2/s.

Does anyone have knowlege about this subject and would be able to help me?

Thanks a lot.

Edited by guiromero, 24 April 2023 - 07:51 PM.

[breizh]

Hi,

Consider his link to clarify your doubts.

https://www.uio.no/s...um-Ch5-2012.pdf

Something is weird with the parenthesis. R*T is part of the exponential.

Yes, Delta Gn is the Gibbs free energy, check in the link.

A relation where units are missing is useless.

No information about the substance?

More investigation is required on your side.

 

note: Google is your ultimate resource.

 

Good luck.

Breizh