## Book 8.11 [ENDORSED]

JennyCKim1J
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### Book 8.11

On page 283, for equation 14, what exactly is Hm (vapor) and Hm (liquid)? Is it related to moles like molar heat capacity (Cm)?

Chem_Mod
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### Re: Book 8.11

I will cover this in class tomorrow.

Hm (vapor) = vapor molar enthalpy

Hm (liquid) = liquid molar enthalpy

Akash_Kapoor_1L
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### Re: Book 8.11

Is there a difference between enthalpy and molar enthalpy?? How would you covert one to the other?

Chem_Mod
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### Re: Book 8.11  [ENDORSED]

Yes there is a difference.

Molar enthalpy is the enthalpy of one mole.

"Enthalpy" can refer to any amount.

If you burnt two moles of methane gas and measured the enthalpy you would divide by 2 mole to get the molar enthalpy (kJ.mol-1).

I will discuss all of this in class.

Wenting Hu 2H
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### Re: Book 8.11

What is the difference between irreversible expansion and reversible expansion?

Audrey Goodman 1F
Posts: 31
Joined: Fri Sep 29, 2017 7:06 am

### Re: Book 8.11

When we're discussing expansion work, the expansion can either be a reversible or irreversible process. A reversible process can be reversed by an infinitesimal change, and reversible isothermal expansion is expansion at a constant temperature where the external pressure matches the pressure of the system. In an irreversible process, it can't be reversed by an infinitesimal change.

Most real world examples are irreversible processes, but hypothetically reversible processes tend to do more work.

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

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