## Exothermic reaction in bond enthalpy example in lecture

Felicia Fong 2G
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am

### Exothermic reaction in bond enthalpy example in lecture

In the lecture today, we did an example about bond enthalpies. CH2=CH2 + H-Br → CH3-CH2Br. The change in enthalpy of the reaction was -58 KJ. Why is this an exothermic reaction?

Posts: 30
Joined: Thu Jul 27, 2017 3:00 am
Been upvoted: 1 time

### Re: Exothermic reaction in bond enthalpy example in lecture

It is exothermic because new bonds are being formed, so energy is being released.

Jakob von Morgenland 2C
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am
Been upvoted: 1 time

### Re: Exothermic reaction in bond enthalpy example in lecture

When we calculated the individual bond enthalpies for the bonds that we broken in the reaction compared to the bonds that were formed, we found that the bond enthalpies of the bonds being formed were larger than the bonds broken. Since the bonds being formed are given negative enthalpies and the bonds being broken are given positive enthalpies, the resulting net enthalpy for the reaction is negative.

Ethan Vuong 3G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### Re: Exothermic reaction in bond enthalpy example in lecture

When bonds are formed, energy gets released. This results in a negative enthalpy, deltaH. If it is negative, then it is exothermic.

Melodie Oh 2A
Posts: 22
Joined: Fri Sep 29, 2017 7:06 am

### Re: Exothermic reaction in bond enthalpy example in lecture

Whenever the enthalpy is negative it is an exothermic reaction as it means that it RELEASES that amount of energy rather than absorbing it.