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Working out a Temperature from Activation Enthalpy watch

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    Hi there Guys!
    If I have the activation enthalpy for a reaction, say 30000J, is there a way of calculating the minimum temperature that the reactants would need to be in order for the reaction to start?
    I tried using that the activation enthalpy/Avogadros No. is equal to the average kinetic energy of one of the molecules, and therefore that that is equal to 3/2kT
    but got an answer of about 2405 Kelvin which is definately not right as the reaction in question progresses quickly at room temperature!

    Any help would be great, i've been trying to crack this for the last half an hour so any suggestions would be amazing!
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    (Original post by doomhalo)
    Hi there Guys!
    If I have the activation enthalpy for a reaction, say 30000J, is there a way of calculating the minimum temperature that the reactants would need to be in order for the reaction to start?
    I tried using that the activation enthalpy/Avogadros No. is equal to the average kinetic energy of one of the molecules, and therefore that that is equal to 3/2kT
    but got an answer of about 2405 Kelvin which is definately not right as the reaction in question progresses quickly at room temperature!

    Any help would be great, i've been trying to crack this for the last half an hour so any suggestions would be amazing!
    well not quite. There isn't really a minimum temperature that the reactants would need to be in order for the reaction to start. That would imply that a reaction is either "on" or "off" It's not.

    The rate of a reaction increases as you increase the temperature according to the Arrhenius Equation:

    k=Ae^{-\frac{E_a}{RT}}

    so it depends what value of k you want to define as "an appreciable rate". Once you have chosen that, you can plug it in the equation and solve for T, thus:

    T=\dfrac{E_a}{R(\ln A - \ln k)}
 
 
 
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