Rates of reaction - kinetics (A2)
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I am trying to find to order of reaction respect to iodine and propanone. A graph of volume of sodium thiosulphate used against time was plotted, and a second graph of slope of the first graph against the volume of propanone added. How do I find the order with respect to propanone?
Corrie writes ...
Your question is a little confusing. I can see why you have plotted a graph of thiosulphate volume (proportional to the amount of iodine in the reaction mixture) vs time. The shape of this graph will tell you whether the reaction is zero, 1st or 2nd order with respect to iodine. Normally in this experiment the concentrations of propanone and acid are in great excess, so only the iodine concentration is decreasing, and the shape of the graph tells you about the order with respect to iodine. It produces an interesting result!
In my experience it is not necessary to plot a second graph, as you have suggested. Surely you mean 'slope of the first graph vs volume of thiosulphate added' - not propanone?
To determine the order with respect to propanone it is necessary to repeat the experiment with everything the same except the propanone concentration which, for example, could be doubled or halved (provided still in excess). Then the slope of the new 'volume (thio) vs time' plot can be compared with the first plot, and the order with respect to propanone deduced - hopefully.
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updated: 28 November 2007
