Is my calculation ok? - clausius clapeyron eq.

[clarkexxx]

I would like to calculate isosteric heat of adsorption (H). I have a series of adsorption isotherms for different temperatures and it appears that the adsorption increases with increasing temperature. This suggests that the process is endothermic. Using Clausius Clapeyron law, the slope of 1/T vs lnC gave me a number of positive value, about 1000, which results in negative H (slope=-H/R), about -8 KJ/mol. I suppose that something is not correct in my calculation as the process should be endothermic. Should not be the deltaH positive? Also, I have applied known equilibrium constant of adsorption to calculate deltaG which is negative , about -7Kj/mol, but decreases with increasing temperature.This would suggest that the adsorption is more favourable at higher temperatures. Do this two conclusions go together well? I am a bit confused.

 

[Navin A S]

Your calculations and conclusions appear to be correct. The isosteric heat of adsorption (H) is a measure of the amount of energy that is released or absorbed when a material is adsorbed onto a surface. In this case, the negative value obtained from the Clausius-Clapeyron equation suggests that the process is endothermic, meaning that it requires energy to be adsorbed. This is consistent with the observation that the adsorption increases with increasing temperature. The negative delta G indicates that the adsorption is more favorable at higher temperatures, which is also consistent with the observations.

 

[quicknote]

Based on your description and calculation, it appears that your calculation for the isosteric heat of adsorption (H) using the Clausius Clapeyron equation is correct. The negative value for H suggests that the process is indeed endothermic, as you have correctly observed from the increase in adsorption with increasing temperature.

The negative value for deltaG also supports this conclusion, as it indicates that the adsorption process becomes more favorable at higher temperatures. This is consistent with the increase in adsorption observed in your isotherms.

It is important to note that the signs of H and deltaG can sometimes be confusing, as they represent different thermodynamic quantities. H represents the heat required for the adsorption process, while deltaG represents the change in free energy. In this case, the negative values for both H and deltaG indicate that the adsorption process is endothermic and becomes more favorable at higher temperatures.

Overall, your conclusions are supported by your calculations and are consistent with the known behavior of adsorption processes. However, it is always a good idea to double-check your calculations and ensure that all assumptions and equations used are appropriate for your system.