Jespersen, Chemistry, General Chemistry New Edition (6th) Chemistry 139 and Chem

Question

Jespersen, Chemistry, General Chemistry New Edition (6th) Chemistry 139 and Chemistry 6e Gradebook Assignment ent PRINTER VERSION BACK NEXT FULL SCREEN ti Reaction Rates and Temperature T The reaction, C2H5Br C2H4 HBr, was observed to have rate constants k 0.0000249 s at 650 K and k 0.000479 s 1 at 427 oC. What is the value of Ea expressed in mol 1? Round your answer to 3 significant figures. mol 1 The number of significant digits is set to 3, the tolerance is +/-2% Question Attempts: o of 1 used SAVE FOR LATER SUBMIT ANSWER Copyright 2000-2014 by John Wiley & Sons, Inc. or related companies. All rights reserved.

Explanation / Answer

by using the arrhenius equation , k = Ae-Ea/RT , where k = rate constant , T=temperature , Ea = activation energy , R=gas constant , let A be the constant for both cases.

in 1st case , T =650K , k=0.0000249 , by putting theses values in the above equation , we have the value of the only unknown Ea = -RT(lnK - lnA ) , so Ea = -5404.1(-10.6-lnA)

now in the 2nd case , k=0.000479 , T = 427+273= 700K , by putting all these values again in the arrhenius equation , the value of the only unknown Ea = -RT(lnK - lnA ) , so Ea =-5819.8(-7.644-lnA)

now we know that lnA is same for both , so , (Ea/-5404.1) +10.6 = (Ea/-5819.8) +7.644

solving the above equation , we get Ea = 223643.275 J/mol = 223.64KJ/mol

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