Signs for Bond Enthalpies

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Venya Vaddi 1L
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Signs for Bond Enthalpies

Postby Venya Vaddi 1L » Tue Jan 29, 2019 9:23 am

Will the bond enthalpy values always be positive for reactants and negative for products, or are there any exceptions to this?

Becky Belisle 1A
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Joined: Fri Sep 28, 2018 12:18 am

Re: Signs for Bond Enthalpies

Postby Becky Belisle 1A » Tue Jan 29, 2019 10:05 am

It should always take energy when breaking bonds and release energy when forming bonds. However, the standard enthalpy of formation for an element is zero when it is in its standard state. For example the bond enthalpy of O2 (Oxygen) is zero.

Fayez Kanj
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Re: Signs for Bond Enthalpies

Postby Fayez Kanj » Tue Jan 29, 2019 5:13 pm

Hello!

Yes, it always takes energy to break a bond, so bond enthalpies are positive values. To break a bond, energy is released, so they are negative values.

Bond making requires energy (+ value) whereas bond breaking releases energy (- value)

Hope this helps :)

sharonvivianv
Posts: 63
Joined: Fri Apr 06, 2018 11:05 am

Re: Signs for Bond Enthalpies

Postby sharonvivianv » Tue Jan 29, 2019 5:23 pm

Bond breaking is an endothermic process while bond forming is an exothermic process!

Stevin1H
Posts: 89
Joined: Fri Sep 28, 2018 12:17 am

Re: Signs for Bond Enthalpies

Postby Stevin1H » Thu Jan 31, 2019 10:50 am

The bond enthalpy values depend on whether there is a bond breaking or bond forming. Since breaking a bond requires energy, this is an endothermic process (positive). And for the formation of bonds, energy is released when this occurs, making it an exothermic process (negative).


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