Using the table of bond dissociation enthalpies, calculate AH for the reaction A
ID: 509159 • Letter: U
Question
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 BDE (kJ/mol) C-X bond BDE (kJ/mol) X2 and HXbonds BDE (kJ/mol) CH3-H CH3-Br 301 Cl-Cl 439 247 Br-Br C2H5-H C2H5-Br 301 192 422 (CH3)2CH-Br 309 LI (CH3)2CH-H 414 151 (CH3) 3C-H 405 (CH3)3 C-Br 305 H-Cl 431 CH2 CHCH2-H 372 CH2 CEICH2-Br 247 H-Br 368 CH2-CH-H 464 H-I 297 Br H Br HBr AH kJ/molExplanation / Answer
For the first propagation step
one allylic C-H bond is broken so energy required = +372 kJ
one H-Br bond is formed = -368 kJ
Thus DElta H of the reaction = +372 -368
= +4 kJ
Endothermic reaction.
second propagation step
one allyl C -Br bond formed = -247 kJ
one Br-Br bond is broken = +192 kJ
thus delta H of the reaction = -247-192
= -55 kJ
Thus the first step of propagation (endothermic reaction) is the rate determining step.
The total delta H of the reaction = sum of delta H of both the steps
= +4 -51 KJ
= -47 kJ
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.