Calculating Activation Energy with Temperature and Time Data

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Discussion Overview

The discussion revolves around calculating the activation energy (Ea) for cooking an egg based on temperature and time data from two different locations with varying boiling points. Participants explore the relationship between temperature, time, and the activation energy using a specific formula, while addressing the challenges posed by unknown rate constants and concentrations.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • The original poster expresses confusion about how to calculate Ea given only temperatures and cooking times, noting the formula requires two unknown rate constants.
  • Some participants suggest rearranging the equation for Ea to solve for it directly, emphasizing the need to identify known and unknown variables.
  • One participant provides the equation for Ea and lists the known temperatures and times, questioning whether to use the times as rate constants.
  • The original poster calculates an Ea value but receives feedback from an online platform indicating the answer is incorrect, possibly due to rounding errors or a mistake in temperature conversion.

Areas of Agreement / Disagreement

Participants generally agree on the approach to rearranging the equation for Ea, but there is uncertainty regarding the use of time as a substitute for rate constants and the accuracy of the calculated value.

Contextual Notes

Participants mention potential roundoff errors and the importance of maintaining accuracy in calculations, as well as a correction made to a temperature conversion that may affect the results.

brandon1
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Homework Statement



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?

Homework Equations



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

k=rate1/(concetrations)

The Attempt at a Solution



Not sure where to start...
 
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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
 
dmoravec said:
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...
 
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:

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