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When heated at high temperature, cyclobutane, C4H8, decomposes to ethylene: C4H8 (g)...

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swimmers | Student | (Level 2) Honors

Posted April 26, 2012 at 3:39 PM via web

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When heated at high temperature, cyclobutane, C4H8, decomposes to ethylene:

C4H8 (g) → 2 C2H4 (g)

 

The activation energy, Ea, for this reaction is 260 kJ/mol. At 800 K, the rate constant is 0.0315 s^-1. Determine the value of the rate constant at 850 K.

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mlsiasebs | College Teacher | (Level 1) Associate Educator

Posted April 26, 2012 at 5:41 PM (Answer #1)

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To determine the value of the rate constant, we can use the Arrhenius equation. 

We can plug in the given values for T1 and T2 (must be in Kelvin), the activation energy (must be in J/mol), R (must use 8.314 J/mol K), and k1.  One important thing to note is that you must correctly pair k1/T1 and k2/T2.

ln (k2/0.315) = (260000 J/mol / 8.314 J/molK)(1/800 - 1/850)

ln (k2/0.315) = 2.30

To get rid of the ln, we need to take both sides to the power of e which will cancel out the ln.

k2/0.315 = e^2.30

k2/0.315 = 9.97

k2 = 3.14

You can go back and check this value by plugging in the temperatures and the k values, then solving for the activation energy.

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