Thank you in advance Use the bond dissociation energies in the table above to ca

Question

Thank you in advance

Use the bond dissociation energies in the table above to calculate the delta H degree value for the addition of HBr to ethene. (delta H for pi bond of ethene = 62 kcal/mol) Calculate the delta H value for the addition of CI_2 to ethene. (delta H for pi bond of ethene = 62 kcal/mol) Do you expect the reactions to be exergonic or endergonic? reaction in Part A is exergonic. reaction in Part B is endergonic both reactions are exergonic reaction in Part A is endergonic, reaction in Part B is exergonic both reactions are endergonic

Explanation / Answer

The energy is required to break the bonds and it is release when the bonds are made.

Delta H is the net sum of these bond energies.

Part A

HBr reacts with ethene to form bromo ethane

Bonds broken are :

Br - Br

Pi bond of ethene

Bonds formed are

CH3 - Br

CH3 - H

Delta H = 53.5 + 62 + (-70.3) + ( -105.0)

Delta H = -59.8 kcal

Part B .

Cl2 reacts with ethene to form 1,2 dichloroethane

Bonds broken are

Cl-Cl

Pi bond of ethene

Bonds formed are

Two CH3 -Cl bonds

Delta H = 58.0 + 62 + ( 2× -83.6)

Delta H = -47.2 kcal

Part C.

Both reactions are exergonic.

Since enthalpy change associated with both the reactions is negative , the reactions release energy and occur spontaneously , hence are exergonic reactions.

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