Bond Enthalpy

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Kimberly 1H
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Joined: Fri Sep 28, 2018 12:17 am
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Bond Enthalpy

Postby Kimberly 1H » Thu Feb 07, 2019 8:53 pm

Why are bond enthalpies always positive?

MackenziePerillo-1L
Posts: 31
Joined: Fri Sep 28, 2018 12:19 am

Re: Bond Enthalpy

Postby MackenziePerillo-1L » Thu Feb 07, 2019 8:58 pm

Bond enthalpy is always positive because it is the energy put into breaking a bond, which is an endothermic process (energy is being put in).

504909207
Posts: 30
Joined: Wed Nov 15, 2017 3:02 am

Re: Bond Enthalpy

Postby 504909207 » Sat Feb 09, 2019 1:13 am

For bond enthalpies are we supposed to know how to draw all of the molecular shapes?

Kevin Tang 4L
Posts: 83
Joined: Fri Sep 28, 2018 12:28 am

Re: Bond Enthalpy

Postby Kevin Tang 4L » Sat Feb 09, 2019 3:49 pm

For the reaction H2O2->1/2 O2 + H2O, The energy needed to break the bonds on the left is 1083kJ and the energy need to break the bonds on the products side is 1174kJ. Why is the delta H = -91kJ and not 91kJ?

Kevin Tang 4L
Posts: 83
Joined: Fri Sep 28, 2018 12:28 am

Re: Bond Enthalpy

Postby Kevin Tang 4L » Sat Feb 09, 2019 3:52 pm

Ok, nevermind I realized my mistake.
Breaking the bonds of the reactants releases 1083kJ of energy and we then have to use 1174kJ of energy to form the bonds to make the products. Thus there is a net negative delta H. So the delta H = -91kJ for the reaction

My mistake was I was looking at the change in energy of the products and the reactants. The products have more energy in form of bonds, which is what I was thinking what I needed to measure.


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