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Marsenne Cabral 1A
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Postby Marsenne Cabral 1A » Thu Jan 31, 2019 7:37 pm

Why is the enthalpy of bonds (delta H b) always greater than zero and endothermic?

Nada AbouHaiba 1I
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Re: Enthalpy

Postby Nada AbouHaiba 1I » Thu Jan 31, 2019 8:06 pm

They're just given as positive values, but if you're forming the bond then you would write them as negative because it is an exothermic process

Toru Fiberesima 1L
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Re: Enthalpy

Postby Toru Fiberesima 1L » Thu Jan 31, 2019 11:19 pm

Bond breaking is an endothermic process ie a process that requires energy. For endothermic reactions, the products of the reaction have a greater enthalpy than the reactants, and heat is absorbed by the system from its surroundings. Therefore, the delta H b must be positive because the energy is being added to the system.

Bruce Chen 2H
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Re: Enthalpy

Postby Bruce Chen 2H » Fri Feb 01, 2019 1:24 pm

Endothermic is using heat, so delta H would be positive, whereas exothermic reactions lose heat so it'll be a negative delta H.

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Re: Enthalpy

Postby Lopez_Melissa-Dis4E » Fri Feb 01, 2019 1:41 pm

Endothermic requires heat, therefore delta H is positive.
Exothermic releases heat, therefore delta H is negative.
Whether you are forming bonds (endothermic), or breaking bonds (exothermic) you would refer to your positive/negative value of delta H.

Xinyi Zeng 4C
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Re: Enthalpy

Postby Xinyi Zeng 4C » Fri Feb 01, 2019 6:25 pm

Just to add on, "enthalpy of bond" has a more formal name as "Bond Energy" and its definition is the amount of energy required to break that particular bond. Breaking of bond requires energy and hence is endothermic.

Charles Gu 1D
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Joined: Fri Sep 28, 2018 12:16 am

Re: Enthalpy

Postby Charles Gu 1D » Fri Feb 01, 2019 11:26 pm

In order to break bonds, you need a input of heat so thats why delta h is positive (endothermic)

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