Activation Energy

[brandon1]

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...

[dmoravec]

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

[brandon1]

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

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....

[brandon1]

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!