A Appendix Reaction rate under non-equilibrium conditions

A Appendix Reaction rate under non-equilibrium conditions 

On a microscopic, molecular level, we can write for a state-selected and state-resolved reaction 

Here ki(T) is the reaction rate constant for a selected state of the reactants. Whether the system is in thermal equilibrium over the internal states of HCl or not, we can rewrite Eq. (A.3.1) as 

Problem E, that this dependence tells us about the entropic requirements of the reaction. We provide a microscopic view of such requirements in Chapter 5. 

In generalpi can depend on time and so Eq. (A.3.3) does not necessarily define a rate constant. If however the system is in thermal equilibrium at the temperature Tthenp, is the Boltzmaim factor for the state i and the averaging in Eq. (A.3.3) defines the familiar thermal reaction rate constant. The point is that Eq. (A.3.3) is valid whether the internal states of the HCl molecules are or are not in thermal equilbrium. 

---