nernst

let’s see what i remember from class today…

[CHEM]

  • always true: oxidation at anode, reduction at cathode (‘red cat’)
  • it follows then that: e- flows from anode to cathode ('a cat’)
  • more positive Eo (standard reduction potential) => more easily reduced
  • It = nF
  • dG = -nFEo
  • Nernst Equation: E = Eo - (RT/nF)lnQ (use for concentration cell questions)
  • Hendersen-Hasslebach: pH = pKa + log ( [A-]/[HA] )
  • “how much needs to be added to dilute…” <–remember already have the starting amount!
5

“Determination of halide concentration by controlled specific ion meter” We basically make a calibration curve by setting two points, a maximum (0.01 M Cl-) and a minimum (0.001 M Cl-)  Fro m this we create a slope of mV.  Which is the “Nernst slope”  This slops is to measure SRP (Standard Reduction Potentials) of atoms and compounds.  This slope should theoretically be 59.2 mV.  It’s a pretty straigh forward lab.  the only problem is our equipment is ancient. 

Section: “Laboratory of  ironies”


Hermann (Walter) Nernst (1864-1941), German physical  chemist.

Nernst (the author of the third law of thermodynamics)  was breeding fishes

in a pond near his cottage. - Why do you bother with  them? - asked his

acquaintance. - Even a poultry breeding seems to be more  interesting. - I

bred animals which are in thermodynamic equilibrium with  the environment. -

replied Nernst. - Breeding homeotherms just means  warming the Universe at

your  expense.

well, this homework is fine, until …

Using the Nernst equation, at room temperature, calculate the reversal potential for K+ (EK) when [K+]out=100 mM and [K+]in = 10 mM.

do i have to?

arxiv.org
[1508.07260] Nernst Effect in Magnetized Plasmas

[ Authors ]
Archis S. Joglekar, Alexander G. R. Thomas, Christopher P. Ridgers, Robert J. Kingham
[ Abstract ]
We present nanosecond timescale Vlasov-Fokker-Planck-Maxwell modeling of magnetized plasma transport and dynamics in a hohlraum with an applied external magnetic field, under conditions similar to recent experiments. Self-consistent modeling of the kinetic electron momentum equation allows for a complete treatment of the heat flow equation and Ohm’s Law, including Nernst advection of magnetic fields. In addition to showing the prevalence of non-local behavior, we demonstrate that effects such as anomalous heat flow are induced by inverse bremsstrahlung heating. We show magnetic field amplification up to a factor of 3 from Nernst compression into the hohlraum wall. The magnetic field is also expelled towards the hohlraum axis due to Nernst advection faster than frozen-in-flux would suggest. Non-locality contributes to the heat flow towards the hohlraum axis and results in an augmented Nernst advection mechanism that is included self-consistently through kinetic modeling.

4

Equations under Non-Standard Conditions

NOT AT 25 degrees C, 1 M, or 1 atm

  1. CELL POTENTIAL (E): Nernst equation for electrochemistry
  2. FREE ENERGY (G)

Simply add standard value (of cell potential or free energy) and deviated value together

arxiv.org
[1508.06427] A local approximation of fundamental measure theory incorporated into three dimensional Poisson-Nernst-Planck equations to account for hard sphere repulsion among ions

[ Authors ]
Yu Qiao, Benzhuo Lu, Minxin Chen
[ Abstract ]
The hard sphere repulsion among ions can be considered in the Poisson-Nernst-Planck (PNP) equations by combining the fundamental measure theory (FMT). To reduce the nonlocal computational complexity in 3D simulation of biological systems, a local approximation of FMT is derived, which forms a local hard sphere PNP (LHSPNP) model. In the derivation, the excess chemical potential from hard sphere repulsion is obtained with the FMT and has six integration components. For the integrands and weighted densities in each component, Taylor expansions are performed and the lowest order approximations are taken, which result in the final local hard sphere (LHS) excess chemical potential with four components. By plugging the LHS excess chemical potential into the ionic flux expression in the Nernst-Planck equation, the three dimensional LHSPNP is obtained. It is interestingly found that the essential part of free energy term of the previous size modified model has a very similar form to one term of the LHS model, but LHSPNP has more additional terms. Equation of state for one component homogeneous fluid is studied for the local hard sphere approximation of FMT and is proved to be exact for the first two virial coefficients, while the previous size modified model only presents the first virial coefficient accurately. To investigate the effects of LHS model and the competitions among different counterion species, numerical experiments are performed for the traditional PNP model, the LHSPNP model, and the previous size modified PNP (SMPNP) model. It’s observed that in steady state the LHSPNP results are quite different from the PNP results, but are close to the SMPNP results under a wide range of boundary conditions. Besides, in both LHSPNP and SMPNP models the stratification of one counterion species can be observed under certain bulk concentrations.