Re: Why dont catalyst have an effect on therodynamics?

A catalyst speeds up a reaction by lowering the activation energy.  The
amount of activation energy needed determines how fast a reaction happens.
 The rate of a reaction is a kinetic property.  Thermodynamics, on the
other hand, refers to whether the reactants or the products of a reaction
are more stable.  If the product is more stable (lower in energy) than the
reactant, then the reaction is thermodynamically favorable, and after
equilibrium is reached, most of the reactant will have been converted into
product.  However, whether a reaction that is thermodynamically favorable
actually occurs at a measurable rate depends on the activation energy.  For
example, the combustion (burning) of your chemistry book is
thermodynamically favored.  However, it is not favored kinetically, because
the activation energy for the combustion reaction is high.  

A catalyst does not change the nature of the reactants or the products, so
the overall thermodynamics are unchanged.  A catalyst only affects the
height of the activation barrier, lowering the energy of activation.

A web site with a nice graphic illustrating the relationship between
kinetics and thermodynamics can be found at:  http://www.eng.auburn.edu/%7Ewfgale/intro_metals/graphics/fig14b_thermo_kinetics.swf