# CCL:G: energy for proton

*From*: David A Case <case++biomaps.rutgers.edu>
*Subject*: CCL:G: energy for proton
*Date*: Fri, 13 Apr 2012 08:28:58 -0400

Sent to CCL by: David A Case [case()biomaps.rutgers.edu]
On Thu, Apr 12, 2012, Alexander Bagaturyants sasha#photonics.ru wrote:
>
> That is, it senseless to calculate formally any thermodynamic function of a
> free (individual) proton.
I think "senseless" is too strong a term here. If you like, you can
think of
reactions like AH -> A- + H+ as half-reactions (as in the corresponding
electron case), and that there will eventually be some proton acceptor in
a "real" equilibrium experiment. But this doesn't vitiate the utility
of
estimating proton affinities (and gas-phase basicities) as standard
thermochemical quantities. Computational estimates using the thermodynamics
of the free proton can be remarkably accurate compared to experiment; of
course, the conversion of raw experimental data to standard-state proton
affinities uses the same model.
As a side note, it is hard to recommend just using Gaussian or any other
program to get such values. The posts that began this thread showed two
outputs, ostensibly from Gaussian:
A. Temperature 298.150 Kelvin. Pressure 1.00000 Atm.
...
Zero-point correction= 0.000000 (Hartree/Particle)
Thermal correction to Energy= 0.001416
Thermal correction to Enthalpy= 0.002360
Thermal correction to Gibbs Free Energy= -0.010654
B. Temperature 298.150 Kelvin. Pressure 1.00000 Atm.
Zero-point correction= 0.000000 (Hartree/Particle)
Thermal correction to Energy= 0.001416
Thermal correction to Enthalpy= 0.002360
Thermal correction to Gibbs Free Energy= -0.010000
Note that the Gibbs free energy values differ by a non-negligible amount.
Of course, no one can ever double-check everything that programs print out,
but here one can do the calculation by hand; see, e.g.
http://www.gaussian.com/g_whitepap/thermo.htm.) [I'm not
sure where how the
"A" value was computed, although I have some guesses.]
...dave case