Rates of reaction - kinetics (A2)
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I am writing up my evaluation for the reaction between sodium thiosulphate and hydrochloric acid, and don't know how to calculate errors in timing the reaction. Could you please tell me how to tackle this, and if not, why it can't be done?
Ulex writes
The answer to this depends on exactly what you were trying to do. There are two possibilities.
1. If you were determining the activation energy.
In this experiment it is quite difficult to repeat a timing at exactly the same temperature as previously used so estimating the error in the timing is not easy. The best way here is to estimate the overall error range in the activation energy itself. When you did your Arrhenius graph, you had to choose the best straight line. Go back to the graph and choose instead the steepest graph you could possibly have chosen and also the least steep one. Use the gradients to calculate a maximum and a minimum value for the activation energy. These are the limits of your error on the whole determination.
2. If you were determining the order of reaction.
You presumably measured the time for complete opacity of the reaction mixture. Judging this moment is not easy. Ask yourself how many seconds you might have been in error here. I know this is a subjective judgment but it is probably the best you can do. Calculate the maximum and minimum values of the rate from the minimum and maximum times and indicate these as uncertainty bars on your subsequent graphs.
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updated: 18 December 2006
