Quasistatic Process Explained: What is dH=δQ+Vdp?

[sphyics]

What is Quasistatic process?

the first law of thermodynamics for a quasitatic process:

dH = δQ + Vdp ------> A

if it is quasi static dp should be very small which can be ignored and hence dH = δQ

so how come the equation "A" holds true for a quasi static process.

 

[Andrew Mason]

What is Quasistatic process?

the first law of thermodynamics for a quasitatic process:

dH = δQ + Vdp ------> A

if it is quasi static dp should be very small which can be ignored and hence dH = δQ

so how come the equation "A" holds true for a quasi static process.

the dP in your equation is the change in pressure of the gas, not the difference between the internal and external pressures. In a quasi-static process dP is not necessarily 0.

For example, in a quasi-static adiabatic expansion, the pressure is constantly decreasing so you have to take into account the ∫VdP term to find the ΔH. So in that case ΔH ≠ ΔQ.

ΔH = ΔQ only if the internal gas pressure is constant during the process.

AM