## Difference between delta H and delta U

Lucia H 2L
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### Difference between delta H and delta U

What is the difference between delta H and delta U? and q for that matter

Sirajbir Sodhi 2K
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Joined: Sat Jul 22, 2017 3:00 am

### Re: Difference between delta H and delta U

Delta H is the change in enthalpy and Delta U is the change in internal energy. Internal energy is the amount of energy a system has. However, we must realize that a system doesn't exist in a vacuum. Rather, there must be some sort of change in volume/pressure because of the presence of a system. If we hold pressure constant, as it often is when a system is introduced, volume must change (we know this from gas laws). This leads us to the concept of enthalpy which is, in essence, a convenient way to MEASURE a system's internal energy at a constant pressure.

The following equation relates the two quantities:

ΔH = ΔU + PΔV

Q is heat -- and is equal to enthalpy at a constant pressure.

Sophie 1I
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Joined: Fri Sep 29, 2017 7:04 am

### Re: Difference between delta H and delta U

Delta H is the change in enthalpy which is equal to change in U +P*change in V and the delta U is the change in internal energy of the system.
q is the heat of the system.

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

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