Are all electrophilic additions exothermic?

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Glenda Marshall DIS 3M
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Joined: Sat Sep 27, 2014 3:00 am

Are all electrophilic additions exothermic?

Postby Glenda Marshall DIS 3M » Mon Mar 09, 2015 4:51 pm

Homework problem 4.29 says

"draw and label the reaction profile with potential energy as the y-axis for the electrophilic addition reaction of hydrogen bromide, HBr, to propene, CH3CHCH2, producing 2-bromopropane, CH3CHBrCH3"

the graph they drew was an exothermic reaction and I am wondering how they determined that from the given data. Thanks!

Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

Re: Are all electrophilic additions exothermic?

Postby Justin Le 2I » Mon Mar 09, 2015 8:28 pm

I think we can assume that the reactions will be exothermic because they will usually be spontaneous. If the reaction were endothermic, it would not be spontaneous.

Chem_Mod
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Re: Are all electrophilic additions exothermic?

Postby Chem_Mod » Tue Mar 10, 2015 9:45 am

The majority of electrophilic addition reactions across a double bond are exothermic because the original carbon-carbon pi bond is generally weak compared to the newly formed single bonds.

Be careful when making statements about spontaneity. Remember that delta G (exergonic or endergonic) is the thermodynamic quantity that tells whether or not a reaction will occur spontaneously. Knowing delta H (exothermic or endothermic) alone does not necessarily tell us if a reaction is spontaneous.


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