Why does cooling down some reactants speed up a chemical reaction?
As a general rule a reaction will be faster at higher temperature. As a rough rule of thumb reaction rate doubles for a 10 deg rise. The only example I can think of where a lower temperature gives a faster reaction would be in complex biological processes where say an enzyme’s activity may be lost at higher temperatures. In his answer, Trevor H is confusing reaction rate and equilibrium concentrations. In the example he quotes the equilibrium will be shifted to more product but this does not mean a faster reaction.
