Hess's Law

Moderators: Chem_Mod, Chem_Admin

Chynna Porrata 1L
Posts: 6
Joined: Fri Sep 25, 2015 3:00 am

Hess's Law

Postby Chynna Porrata 1L » Mon Jan 11, 2016 12:11 am

When calculating for the change in enthalpy and canceling compounds, must they be on separate sides of the arrows in the two reactions? As in a compound in the reactant side cancels out when that same compound is on the product side of the other reaction.

Chem_Mod
Posts: 18880
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 714 times

Re: Hess's Law

Postby Chem_Mod » Mon Jan 11, 2016 9:09 am

Yes they have to be in the opposite side to be able to cancel out. You can think of it as an equation. You have to have 2 identical term in 2 sides of an equation to be able to cancel them out. Just make sure that they have the same number of mole.

704628249
Posts: 43
Joined: Fri Sep 25, 2015 3:00 am

Re: Hess's Law

Postby 704628249 » Mon Jan 11, 2016 9:35 am

Yes, they would have to be on opposite sides.

Yunna Gu
Posts: 26
Joined: Fri Sep 25, 2015 3:00 am

Re: Hess's Law

Postby Yunna Gu » Mon Jan 11, 2016 1:04 pm

Remember that when you flip the sides you have to multiply the delta H by a negative sign. And when you multiply the equation, you also have to multiply the delta H by the same number!


Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

Who is online

Users browsing this forum: No registered users and 2 guests