Re: Microscopic Reversibility


"dkomo" <dkomo871@xxxxxxxxxxx> wrote in message news:z7Wdna8wpbF6J2HZnZ2dnUVZ_tmdnZ2d@xxxxxxxxxxxxxx
rev.goetz wrote:

I am hoping that a chemist can answer a question about the law of
chemistry called "microscopic reversibility."


It means A <=> B where A is a set of chemical reactants and B is a set
of products. The double arrow means the reaction flows in either
direction, but not necessarily at the same rate.

Does microscopic reversibility imply that any chemical chain reaction
can reverse itself regardless of the unlikelyness of the reverse
reaction?


Of course not. The following law governing the reactions must be obeyed:

deltaG = deltaH - T * deltaS

where deltaG is the change in free energy
deltaH is the change in enthalpy
deltaS is the change in entropy
T is the temperature


True enough, though that doesn't by iself tell you the direction the reaction
will go. For this, you would need a second principle - something like
"in spontaneous reactions, deltaG will be negative". But that is not exactly
correct either, as described below.

When the reaction is in equilibrium, the concentrations of all the
reactants and products doesn't change. This is a dynamic equilibrium
because the A <=> B process is still going on, in both directions, and
normally at different rates.

True.

At equilibrium, deltaG = 0 for the
bidirectional process. There is no longer any free energy available to
change the concentrations of the reactants and products.

False. The correct formulation uses Boltzmann's formula - roughly:

At equilibrium
[reactants] / [products] = e ^ (deltaG / kT).
where [___] means concentration of ___

If you start with all reactants, then the reaction will proceed to the
right until equilibrium is reached. If you start with all products,
the reaction will proceed (reverse reaction) to the left until
equilibrium is reached. Same equilibrium in either case.

.

Relevant Pages

  • Re: Microscopic Reversibility
    ... The double arrow means the reaction flows in either ... can reverse itself regardless of the unlikelyness of the reverse ... reactants and products doesn't change. ... This is a dynamic equilibrium ...
    (talk.origins)
  • Re: Proof of equilibrium for elementary A to B rxn
    ... >rate equations alone, w/out any knowledge of equilibrium, can you ... >elementary rxn, and shows the rate and conc of reactants and products. ... the rate of the reverse reaction is zero. ...
    (sci.chem)
  • Re: Microscopic Reversibility
    ... The double arrow means the reaction flows in either direction, but not necessarily at the same rate. ... can reverse itself regardless of the unlikelyness of the reverse ... where deltaG is the change in free energy ... When the reaction is in equilibrium, the concentrations of all the reactants and products doesn't change. ...
    (talk.origins)
  • Re: Microscopic Reversibility
    ... The double arrow means the reaction flows in either ... can reverse itself regardless of the unlikelyness of the reverse ... For equilibrium, the two directions must proceed at the *same* rate. ...
    (talk.origins)
  • Re: "Proteins cant form in water as water will brake the bonds that
    ... the rate of increase is the same in both directions. ... concentrations of products and reactants. ... things to deal with reaction dynamics. ... Next, if you increase the forward rate 1000 fold, and the reverse ...
    (talk.origins)