Question regarding Enthalpy

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Cecilia Tsai 3C
Posts: 16
Joined: Fri Sep 25, 2015 3:00 am

Question regarding Enthalpy

Postby Cecilia Tsai 3C » Sun Jan 10, 2016 4:42 pm

Is it true that the delta H value for the forward reaction is negative the delta H value for the reverse reaction?

If so, please explain why this is true.

KVu 3G
Posts: 12
Joined: Fri Sep 25, 2015 3:00 am

Re: Question regarding Enthalpy

Postby KVu 3G » Sun Jan 10, 2016 5:12 pm

Yes it is true, I like to think of this in terms of a reaction profile. For example, say the reactants have a lower energy than their products. That means that the reaction is endothermic and requires energy. However, once you switch them, and go from products to reactants, you're now going from a high energy level to a lower energy level, but the delta H value is still the same, it's simply the negative of the forward reaction. Sorry if this was confusing, here's a bad paint picture of what I'm trying to say.
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endoprofile.png
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LinaLi2E
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Re: Question regarding Enthalpy

Postby LinaLi2E » Sun Jan 10, 2016 5:19 pm

Yes. The delta H for the forward reaction is negative of the delta H of the reverse reaction. It is easier to think of it the other way though. delta H of the reverse reaction=-(delta H of forward reaction) because the forward reaction is what is given so if you reverse the reaction, you are essentially switching the process. Lets say that the delta H for the forward reaction is positive, then that means that the reaction is endothermic. If you want the reverse reaction, then the delta H must be negative because the opposite of endothermic is exothermic. So the forward reaction absorbs heat from the surroundings while the reverse reaction release heat to the surroundings. Hopes this help.


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