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Is it reasonable to derive this formula?

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**Wienerbroed**:

I need to calculate the change in internal energy of a reaction.

Is it reasonable to derive the formula ΔU = ΔH - P * ΔV to ΔU = ΔH - nRT?

In this case the pressure is constant, meaning ΔH = q. All terms should then have the unit joules.

I don't have a measurement for the volume.

**Orcio_Dojek**:

True, as pΔV = Δn RT.

**Borek**:

--- Quote from: Orcio_Dojek on July 07, 2021, 01:27:53 PM ---True, as pΔV = Δn RT.

--- End quote ---

n and Δn are not synonyms.

**Orcio_Dojek**:

Right, I hope that Wienebroed sees the difference in his equation.

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