Activation Energy

  1. 1. The problem statement, all variables and given/known data

    In Houston (near sea level), water boils at 100.0°C. In Cripple Creek, Colorado (near 9500 ft), it boils at 90.0°C. If it takes 5.6 min to cook an egg in Cripple Creek and 4.5 min in Houston, what is Ea for this process?


    What I do not understand is how I can figure this when the given formula for find Ea involves 2 unknown rate constants, and the formula for finding the rate constant given involves concentrations? So, how can I find the activation energy when given only 2 temperatures and 2 times?

    2. Relevant equations

    ln(k2/k1)=(-Ea/R)[(1/T2)-(1/T1)]^-1

    k=rate1/(concetrations)

    3. The attempt at a solution

    Not sure where to start...
     
  2. jcsd
  3. well, you have an equation for Ea... rearrange it to solve for Ea.

    What variables do you know? What variables do you need?

    hint: you might not have to solve for each k value individually
     
  4. Ea=-R(ln k2/k1)[(1/T2)-(1/T1)]^-1

    Ea=?
    T2=363.0K
    T1=372.0K
    time1=336s
    time2=270s
    R=8.314 J/mol*k

    Do I plug in the times for k? I am attempting it now, it looks as if it should still all cancel and leave me with J/mol which I want....
     
  5. Ok, I came up with 27279.97791 J/mol corrected to 27000 J/mol for sig figs, but Webassign says I am wrong, and within 10% of the correct answer. "Your answer is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least four-digit accuracy to minimize roundoff error."


    Edit: I wrote a temp incorrectly in my conversion. Correct now!
     
    Last edited: Feb 22, 2007
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