In the reaction between iodine and propanone, why is the rate of reaction independent of the iodine concentration?
Ulex replies This is a consequence of the accepted mechanism for the reaction, and part of the evidence in favour of this mechanism. The reaction proceeds via a number of stages; each of which is a separate chemical reaction. One of these stages is inevitably going to be slower than the others, and the overall reaction cannot go faster than this slowest stage. Any reactant (in this case iodine) which only takes part in a stage after the slowest one cannot change the rate of the reaction. You recognise this effect by the fact that when you determine the rate equation for the reaction, the order for iodine turns out to be zero. There is quite a neat analogy to try to explain this effect in the Nuffield Chemistry Students Book p 251. Risk assessment Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. Y
