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

In summary, a quasistatic process is a thermodynamic process that is carried out at an infinitely slow rate, causing the pressure difference to be negligible. However, in the first law of thermodynamics, the equation dH = δQ + Vdp is still applicable, even for quasi-static processes. This is because in a quasi-static process, the change in pressure (dP) is the change in pressure of the gas, not the difference between the internal and external pressures. Therefore, in certain cases, such as a quasi-static adiabatic expansion, the ∫VdP term must be taken into account to find the change in enthalpy (ΔH), which is not necessarily equal to the change in
  • #1
sphyics
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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.
 
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  • #2
sphyics said:
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
 

1. What is a quasistatic process?

A quasistatic process is a thermodynamic process that occurs slowly enough for the system to remain in thermodynamic equilibrium at all times. This means that the system is able to adjust to any changes in its environment without any fluctuations in temperature, pressure, or other thermodynamic properties.

2. What does "dH=δQ+Vdp" mean in the context of a quasistatic process?

This equation is known as the First Law of Thermodynamics and it describes the change in enthalpy (dH) of a system in terms of the heat transfer (δQ) and work (Vdp) done on the system. In a quasistatic process, dH represents the change in the internal energy of the system, δQ represents the heat added to or removed from the system, and Vdp represents the work done by or on the system.

3. How is a quasistatic process different from a dynamic process?

In a dynamic process, the system changes rapidly and is not able to maintain thermodynamic equilibrium. This means that temperature, pressure, and other thermodynamic properties may fluctuate during the process. In contrast, a quasistatic process occurs slowly enough for the system to remain in equilibrium at all times.

4. What is the significance of a quasistatic process in thermodynamics?

The concept of a quasistatic process is important in thermodynamics because it allows us to make simplifications and assumptions about the behavior of a system. By assuming that a process is quasistatic, we can use theoretical models and equations to predict the behavior of a system without having to consider the complexities of a dynamic process.

5. Can a real-life process be considered quasistatic?

In theory, any process can be considered quasistatic if it occurs slowly enough. However, in real-life situations, processes often occur too quickly for the system to remain in equilibrium at all times. Therefore, while quasistatic processes are useful in theoretical models, they may not accurately describe real-world processes.

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