## Delta H

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

### Delta H

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

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

Posts: 60
Joined: Tue Nov 28, 2017 3:02 am

### Re: Delta H

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

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

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
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Joined: Wed Nov 15, 2017 3:04 am

### Re: Delta H

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

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

### Re: Delta H

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

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!

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