I am conducting a study on transition state. In order to determine the activation energy, I will use the formula
∆G = ∆H -T∆S
And in order to solve for ∆H, I use the formula
H = E + ZPE + RT
In order to solve for entropy, I use the formula
S = R ln Q
Where Q is calculated as
Q= e (-E/kT)
And Q tot is
Qtot= Q1*Q2*Q3
Am I using the right formulas? Also, I still need more references or studies that uses the same formulas. I hope somebody can help me. Thank you.
Yes, you can use the formula S = R ln Q to calculate entropy under certain conditions.
Here, S is the entropy of the system, R is the gas constant, and Q is the number of microstates associated with a particular macrostate of the system.
This formula is typically used for calculating the entropy of an ideal gas system, where Q is the total number of possible arrangements of the gas particles in the given system.
However, it is important to note that this formula applies only under certain conditions and assumptions, and may not be applicable in all cases. In particular, it assumes that the system is in thermal equilibrium and that its internal energy is uniformly distributed among all its accessible microstates.
In general, calculating the entropy of a system can be a complex task that requires a thorough understanding of the system and its thermodynamic properties
Dear Trisha M Castilla
As the previous Professor right explained, it can be used in some particular cases with gases, mainly in those where the degrees of freedom are known.
Let us say for example that we want to know the partition function Q of a particular gas if we know the degrees of freedom,.
Thus, the term coined as Q can be decomposed and a temperature increases there will be more degrees of freedom contributing to different thermodynamic quantities & that equation serves well for the heat capacity:
Q = Qtrasl Qelec Qvib Qrot
However, we ought to remember that entropy has different contextual meanings, and that only Qtrasl (V;T); The other Qs only dependent on T, that gives two kinds of entropy:
- Thermal entropy.
- Configurational entropy.
Kind Regards.
Thank you Pedro L. Contreras E. I was using those formulas to calculate for the activation energy of the sn2 reaction with a formula Ea= deltaG (Transition state) - deltaG (reactants). I would very much appreciate it if you can enlighten me more on the formulas that I should use. Thank you and more power!
Dear Trisha M Castilla
Since I am a physicists that worked years ago with a team of Theoretical Chemists, I only can advice you the following according to my personal view:
There are subtle differences in teaching Physico Chemistry I & II courses in Chemistry & Statistical Thermodynamics courses in Physics
For Chemists, I recommend this classical book that seems to be more related to the calculation you need:
Physical Chemistry by Peter Atkins, Julio de Paula, and James Keeler, 2018, Oxford University Press.
For Physicists, I recommend the following classical text:
Statistical Mechanics by R. Kubo and coauthors, (1965) North Holland.
You can see there that in the 1st & 2nd cases, the label for the entropy is different.
Intuitively, I guess the Third Law of Thermodynamics plays a fundamental role on the interpretation.
Kind Regards.
- Badges
- Science topic