CH353 - Physical Chemistry I
Spring 2015, Unique 51170

Lecture Summary, 30 April  2015

Fast Equilibrium:  The steady-state approximation is usually most useful for reactions in which the first elementary step is the slowest (i.e. rate determining).  Sometimes that is not the case, and the intermediate created in the first or first few elementary steps builds up over time before it is consumed:

  [I] = K(c)[R]

Both the SSA and FE assumptions allow us to solve for [I] in terms of [R] and/or [P], which in turn will solve for a rate law.  This rate law always must be compared to the experimentally observed rate law to determine if it is correct.  If not, then one or more of our assumptions has been wrong, and we need to rethink the problem.