Using the table of bond dissociation enthalpies, calculate ? H ° for the reactio

Question

Using the table of bond dissociation enthalpies, calculate ?H° for the reaction A.

(Use the entries for propene and propenyl halides for the calculation of cyclohexene and cyclohexenyl halides, respectively. Pay attention to the algebraic sign of your answer!)

Using the table of bond dissociation enthalpies, calculate AH° for the reaction A (Use the entries for propene and propenyl halides for the calculation of cyclohexene and cyclohexenyl halides, respectively. Pay attention to the algebraic sign of your answer!) Table of bond dissociation enthalpies C-H bond CH3-H C2H5-H C-X bondBDE (kJ/mol)X2 and HX bonds CH3-I C2H5-I (CH3)2CH-I 238 (CH3)3C-I CH2-CHCH2-I192 BDE (kJ/mol) 247 192 151 431 368 297 BDE (kJ/mol) C1-Cl 439 422 (CH)2CH-H 414 405 CH2-CHCH2-H 372 464 242 238 Br-Br H-Cl H-Br H-I (CH3)3C-H 234 CH2-CH-H + HI AHD- kJ/mol The following are the propagation steps of reaction A st CH2 + HI nd CH2 Calculate H° for each propagation step AH for the 1St step is AH for the 2nd step is Which propagation step is rate-determining? kJ/mol kJ/mol

Explanation / Answer

In the first step of reaction A,

one CH2=CHCH2-H bond is broken and one H-I bond is formed.

Thus dH for this step is : 372-297 = 75 kJ/mol

In the second step, one I-I bond is broken and one CH2=CHCH2-I bond is formed

Thus dH for this step is : 151-192 = -41 kJ/mol

Net dH = 75-41 = 34 kJ/mol

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