Rates of reaction - kinetics (A2)
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My extended essay topic is on how most textbooks say if you increase the temperature by 10 K, you double the rate of reaction. I have investigated 3 different reactions, hydrochloric acid and magnesium, hydrochloric acid and sodium thiosulphate, potassium iodide and hydrogen peroxide (iodine clock). My results say that the iodine clock is nearest to the literature prediction and the HCl and magnesium is furthest. Why is this? Is it something to do with steric effects and enthalpy changes?
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Ulex replies
The 10 K rule of thumb arises because of the Arrhenius equation, which relates the logarithm of the rate constant to the temperature. If the difference in temperature is +10 K, the difference in k is proportional to the log of 10, which is 1. So k increases by another k, i.e. it doubles. If the concentrations of the reactants are exactly the same, ideally the rate should double with a 10 K increase of temperature.
I wonder, firstly, if you really were able to control the concentrations so precisely and, secondly, how close the rates were to the predicted ones. Are we talking about a big discrepancy or only a small one?
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updated: 28 July 2008
