Turn on thread page Beta

Working out a Temperature from Activation Enthalpy watch

    • Thread Starter
    Offline

    2
    ReputationRep:
    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!
    Offline

    13
    ReputationRep:
    (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)}
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: April 15, 2011

University open days

  • University of Exeter
    Undergraduate Open Days - Exeter Campus Undergraduate
    Wed, 24 Oct '18
  • University of Bradford
    Faculty of Health Studies Postgraduate
    Wed, 24 Oct '18
  • Northumbria University
    All faculties Undergraduate
    Wed, 24 Oct '18
Poll
Do protests make a difference in political decisions?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.