Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In a mixed-order reaction the order of a reaction changes in the course of a reaction as a result of changing variables such as pH. An example is the oxidation of an alcohol to a ketone by a ruthenate (RuO42 ) and a hexacyanoferrate, the latter serving as the sacrificial catalyst converting Ru(IV) back to Ru(VI) : the disappearing-rate of the ferrate is zero-order with respect to the ferrate at the onset of the reaction (when its concentration is high and the ruthenium catalyst is quickly regenerated) but changes to first-order when its concentration decreases.