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Homework Help: Activation Energy formula

  1. Feb 22, 2007 #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



    3. The attempt at a solution

    Not sure where to start...
  2. jcsd
  3. Feb 22, 2007 #2
    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. Feb 22, 2007 #3
    Ea=-R(ln k2/k1)[(1/T2)-(1/T1)]^-1

    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. Feb 22, 2007 #4
    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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