## Enthalpy equation

Arjun Sharma 1D
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Enthalpy equation

In the equation H= U + PV, where does the PV at the end come from?

Emily Duggan 1F
Posts: 42
Joined: Fri Sep 29, 2017 7:07 am

### Re: Enthalpy equation

It comes from the equation for calculating internal heat when changing the energy of a closed system at a constant pressure. That equation is U = H - PV, so when rearranged you can get H = U + PV

hope this helps!

camrynpatterson3C
Posts: 44
Joined: Fri Sep 29, 2017 7:07 am

### Re: Enthalpy equation

Work, at constant pressure, is equal to -PdeltaV.
The change in internal energy of a system is equal to q + w. Therefore, deltaU is equal to q + (-PdeltaV).
At constant pressure, q is equal to deltaH.
So, deltaU = deltaH + (-PdeltaV).

Hope that helps a little.

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