Hess's Law depends on enthalpy as a state function

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Josephine Lu 4L
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Joined: Fri Sep 28, 2018 12:18 am

Hess's Law depends on enthalpy as a state function

Postby Josephine Lu 4L » Sun Feb 03, 2019 11:04 pm

Why does Hess's law depend on the fact that enthalpy is a state property?

Samantha Kwock 1D
Posts: 61
Joined: Fri Sep 28, 2018 12:24 am

Re: Hess's Law depends on enthalpy as a state function

Postby Samantha Kwock 1D » Sun Feb 03, 2019 11:10 pm

Hess's law allows you to add two reaction enthalpies together to determine the reaction enthalpy of a third reaction. If enthalpy were not a state function, its value would be dependent on the pathway it took to form the products. This would then invalidate the method of adding two other reaction enthalpies together as this would be a different pathway than the third composite reaction and a different enthalpy value.

Nahelly Alfaro-2C
Posts: 59
Joined: Wed Nov 15, 2017 3:04 am

Re: Hess's Law depends on enthalpy as a state function

Postby Nahelly Alfaro-2C » Sun Feb 03, 2019 11:17 pm

Remember that state properties do not depend on a path taken to obtain that state and they can also be added or subtracted. Therefore changes in enthalpy (Hess's Law) are additive like a state function. In addition, enthalpy change at each step of a multi-step reaction can be additive to give the total enthalpy change.

Catly Do 2E
Posts: 64
Joined: Fri Sep 28, 2018 12:24 am

Re: Hess's Law depends on enthalpy as a state function

Postby Catly Do 2E » Sun Feb 03, 2019 11:36 pm

Hess's Law states that the heat of a specific reaction is equal to the sum of the heats of reaction. This depends on the fact that enthalpy is a state function because state function values do not depend on the path that is taken to reach that specific value. Therefore, it is okay to add/subtract these values, as stated in Hess's Law. If enthalpy was not a state function, Hess's Law would be false.


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