Question

Why do we use two different formulas in thermodynamics in *chemistry* ; ΔU = q + w & ΔH = ΔU + ΔnRT ?

Answer 1

Hey dear,

Both the formulas are same, they are used upon situations. Let me prove it first.

we know,

W = Pdv

Also, PV = NRT , from ideal gas equation.

differentiating both sides...

pdv + vdp = d(nrt)

since, in processes , rxn occurs at a constant pressure .Generally, they change abruptly. So, vdp = 0.

So, Vdp = d(nrt).

Hence, we can use both the formulas.