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Thermodynamic and Kinetics of Chemical reactions
By
Dr. Mehboob Peeran

Let us examine the energy profile of a chemical reaction.

Energy Profile of a Chemical Reaction
An example
CH3 Cl + OH- CH3OH + Cl-

The following data is associated with the reaction

The equilibrium constant K = 1016 ΔGo = -22Kcal / mol. ΔHo = -18 Kcal / mol, ΔSo = +13 Cal-1deg-1

a) The driving force is large, that is, it has a large equilibrium constant, a large negative free energy change and a favourable entropy change

b) The C-O bond is stronger than C-Cl bond.

Yet 0 .05M solution of CH3Cl mixed with 0.1M NaOH, the reaction is not even 10% complete in two days at room temperature.

This is because the reaction has favourable thermodynamics but the activation energy barrier is too large, unless it is overcome the reaction will not take place.

This is achieved by supplying energy by heating the reaction mixture. Increase in temperature by 100o C doubles the rate of a reaction ( This is referred to as temperature coefficient ).

It is interesting to speculate what would happen if one fine morning the height barrier for the flow of water and the energy barrier for chemical reactions disappear? Well for one thing, that morning would most definitely will not be a fine morning.

Any speculations? (mpeeran@gmail.com)

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