Hess's Law

Moderators: Chem_Mod, Chem_Admin

Diana Chavez-Carrillo 2L
Posts: 122
Joined: Fri Sep 28, 2018 12:18 am

Hess's Law

Postby Diana Chavez-Carrillo 2L » Sat Feb 08, 2020 11:31 pm

Since Hess's Law can be used for both enthalpy and entropy since they are both state functions and extensive properties, why is there no delta on the S for entropy as shown by its equation: ∆S°rxn = ∑ S° products - ∑ S° reactants but there is one for enthalpy: ∆H°rxn = ∑ ∆H° f products - ∑ ∆H° f reactants?

Adam Kramer 1A
Posts: 103
Joined: Sat Aug 24, 2019 12:15 am

Re: Hess's Law

Postby Adam Kramer 1A » Sat Feb 08, 2020 11:50 pm

I believe that it has the same relationship as Hess's law because they are both state functions (entropy and enthalpy), but they are not exactly the same because Hess's law only applies to enthalpy. There is a very similar relationship, but they are different because we cannot track H alone. It is usually written as delta H because it is a relative measurement from the previous state to the next, unlike entropy, which we can track in its current state.

Diana Chavez-Carrillo 2L
Posts: 122
Joined: Fri Sep 28, 2018 12:18 am

Re: Hess's Law

Postby Diana Chavez-Carrillo 2L » Sun Feb 09, 2020 12:01 am

Adam Kramer 1A wrote:I believe that it has the same relationship as Hess's law because they are both state functions (entropy and enthalpy), but they are not exactly the same because Hess's law only applies to enthalpy. There is a very similar relationship, but they are different because we cannot track H alone. It is usually written as delta H because it is a relative measurement from the previous state to the next, unlike entropy, which we can track in its current state.


Oh, I see! Wow, that makes more sense thank you so much for clarifying that!


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