Steve Marsden’s

Once we know that some reactions do not "go to completion" and can relate that fact approximately to the standard free energy change of the process, it is natural to wonder if there are things we can do to change the extent of reaction.

We already know that temperature has an effect on the spontaneity of some reactions. In many cases it determines whether a process will be spontaneous or not. But are there other factors? And what exactly are the effects? To answer those and other questions we did a few simple experiments in class.

The first experiment concerned the aqueous equilibrium system shown below:

Cr2O72- + H2O CrO42- + 2 H+

This mixture forms by itself when orange dichromate ions are placed in solution. In an attempt to discern the effect of changing concentration on this equilibrium we added acid to one sample and base to another.