Delta H

Moderators: Chem_Mod, Chem_Admin

jlinwashington1B
Posts: 65
Joined: Fri Sep 28, 2018 12:22 am

Delta H

Postby jlinwashington1B » Fri Feb 08, 2019 11:09 am

What does this refer to, and what’s the equation for it?

Elle_Mendelson_2K
Posts: 72
Joined: Fri Sep 28, 2018 12:28 am

Re: Delta H

Postby Elle_Mendelson_2K » Fri Feb 08, 2019 11:19 am

Delta H is the change in enthalpy. H = U + PV is one of the equations.

Jerome Mercado 2J
Posts: 60
Joined: Tue Nov 28, 2017 3:02 am

Re: Delta H

Postby Jerome Mercado 2J » Fri Feb 08, 2019 11:26 am

Delta H is enthalpy of the system. When pressure is constant, Delta H can tell you if the system is absorbing or losing energy in the form of heat. A negative H is the loss of heat while a positive H is the absorption of heat.

The equation of the enthalpy of the system is the summation of H of the products subtracting the summation of H of the reactants.
To do this method you may need to know all the standard enthalpies of formation of each substance.

deltaH = delta H (products) - delta H (reactants)

Or

When change in enthalpy is reliant on work and internal energy:

deltaH = (q + w) + PdeltaV

Aria Soeprono 2F
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

Re: Delta H

Postby Aria Soeprono 2F » Fri Feb 08, 2019 12:29 pm

It's also important to note that enthalpy is additive because of Hess's Law. It is a state function, so the change in enthalpy (Delta H) at each step of a multistep reaction can be added to get the total enthalpy change.

Tarika Gujral 1K
Posts: 62
Joined: Fri Sep 28, 2018 12:27 am

Re: Delta H

Postby Tarika Gujral 1K » Fri Feb 08, 2019 12:39 pm

You can also use bond enthalpies to determine delta H:
Delta H = H bonds broken (reactants - H bonds formed (products)

But this is not always accurate, as it uses average enthalpy values for the bonds.

Ashley P 4I
Posts: 64
Joined: Wed Nov 15, 2017 3:04 am

Re: Delta H

Postby Ashley P 4I » Sat Mar 16, 2019 1:23 pm

Because it is a state function, it means that you can add/subtract two different delta H’s correct?

Milena Aragon 2B
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

Re: Delta H

Postby Milena Aragon 2B » Sat Mar 16, 2019 1:26 pm

Ashley P 4I wrote:Because it is a state function, it means that you can add/subtract two different delta H’s correct?


Yes, if you're asked to find the total enthalpy change you can add/subtract enthalpy values from multiple reactions

Ashley P 4I
Posts: 64
Joined: Wed Nov 15, 2017 3:04 am

Re: Delta H

Postby Ashley P 4I » Sat Mar 16, 2019 1:28 pm

Milena Aragon 2B wrote:
Ashley P 4I wrote:Because it is a state function, it means that you can add/subtract two different delta H’s correct?


Yes, if you're asked to find the total enthalpy change you can add/subtract enthalpy values from multiple reactions


Thank you so much!


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 0 guests