[Physics Class Notes] on Thermodynamic Processes Pdf for Exam

We know that there are various methods that can be taken to get a Thermodynamic system from its beginning state to its ultimate state. We’ll talk about those Thermodynamic processes in this article. We’ll look at what a quasi-static process is first. State variables are defined only when the Thermodynamic system is in equilibrium with its surroundings, as previously explained. A quasi-static process is one in which the system is in Thermodynamic equilibrium with its surroundings at all times.

In a refrigerator, how does food stay cold and fresh? Have you ever noticed that even when a refrigerator’s entire inside compartment is chilly, the outside or back of the refrigerator is warm? Here, the refrigerator extracts heat from its interior and transmits it to the surrounding area. This is why a refrigerator’s back is warm. Thermodynamic processes are the movement of heat energy within or between systems.

A Thermodynamic system is a specific space or macroscopic region in the universe, whose state can be expressed in terms of pressure, temperature, and volume, and in which one or more than one Thermodynamic process occurs. Anything external to this Thermodynamic system represents the surroundings and is separated from the system by a boundary. The surroundings, system, and the boundary, together constitute the universe. Types of systems in Thermodynamics are as follows:

• Open System: It allows energy as well as mass to flow in and out of it.

• Closed System: It only allows energy (work and heat) to be transferred across its boundary.

• Isolated System: Neither mass nor energy is allowed to interact with it.

In the winter, rubbing your palms together makes you feel warmer. Because touching our palms produces heat, this happens. The heat of the steam is also used in steam engines to move the pistons, which causes the train wheels to rotate. But what is the actual procedure here? This is related to a phenomenon known as ‘Thermodynamics.’

The study of the relationship between heat, work, temperature, and energy is known as Thermodynamics. Thermodynamics is concerned with the movement of energy from one location to another and from one form to another in its broadest definition. The essential concept is that heat is a sort of energy that correlates to a specified quantity of mechanical labor.

The heat was not formally recognized as a form of energy until around 1798, when Count Rumford (Sir Benjamin Thompson), a British military engineer, discovered that infinite amounts of heat might be produced while boring cannon barrels, and that the quantity of heat produced is proportionate to the amount of work done in spinning a blunt boring instrument. The foundation of Thermodynamics is Rumford’s observation of the relation between heat created and work done. Carnot’s research focused on the limits to the maximum amount of work that a steam engine can produce when using a high-temperature heat transfer as its driving force. Rudolf Clausius, a German mathematician, and physicist, refined these ideas into the first and second laws of Thermodynamics later that century.

Types of Thermodynamic Processes

The state of a given Thermodynamic system can be expressed by various parameters such as pressure (P), temperature (T), volume (V), and internal energy (U). If any two parameters are fixed, say, pressure (P) and volume (V) of a fixed mass of gas, then the temperature (T) of the gas will be automatically fixed according to the equation PV =RT. No change can be made to T without altering P and V.

The state of a system can be changed by different processes. In Thermodynamics, types of processes include:

• Isobaric process in which the pressure (P) is kept constant (ΔP =0).

• Isochoric process in which the volume (V) is kept constant (ΔV =0).

• Isothermal process in which the temperature (T) is kept constant (ΔT =0).

• Adiabatic process in which the heat transfer is zero (Q=0).

Thermodynamic process notes have been discussed later.

Work in Thermodynamic Processes

When the volume (V) of a system alters, it is said that pressure-volume work has occurred. A Thermodynamic process occurring in a closed system in such a way that the rate of volume change is slow enough for the pressure (P) to remain constant and uniform throughout the system, is a quasi-static process. In this case, work (W) is represented as:

δW = PdV, where δW is the infinitesimal work increment by the system, and dV is the infinitesimal volume increment.

Also, W = [int] PdV, where W is the work the system does during the entire reversible process.

Isobaric Process

Since the pressure (P) is constant in this process, the volume of the system changes. The work (W) done can be calculated as W = P (Vfinal – Vinitial).

If ΔV is positive (expansion), the work done is positive. For negative ΔV (contraction), the work done is negative.

Isochoric Process

The volume remains constant in an isochoric process. Therefore, the system does not do any work (since ΔV = 0, PΔV or W is also zero). Such a process in which there is no change in volume can be achieved by placing a Thermodynamic system in a closed container that neither contracts nor expands. Thus, from the first law of Thermodynamics (Q = ΔU + W), the change in internal energy becomes equal to the heat transferred (ΔU = Q) for an isochoric process.

Isothermal Process

The temperature of the system remains constant in an isothermal process. We know,

W = [int] PdV

From Gas Law, 

PV = nRT

P = nRT/V. Using the value of P in the work equation:

W = nRT VB [int]VA (dV/V)

W = nRT ln (VB/VA)

If VB is higher than VA, the work done will be positive, or else negative.

Since internal energy is temperature-dependent, ΔU = 0 because the temperature is constant, and thus, from the first law of Thermodynamics (Q = ΔU + W), we will get Q = W.

Adiabatic Process

No heat is exchanged with the system in an adiabatic process (Q = 0). Its mathematical representation is:

 PVƔ = K (constant).

Also, W =  [int] PdV. Substituting the value of P in the work equation:

W = K Vf [int]Vi (dV/VƔ)

W = K [(Vf1-Ɣ – Vi1-Ɣ)/ 1-Ɣ]

Since Q = 0 for an adiabatic process, from the first law of Thermodynamics (Q = ΔU + W), we will get ΔU = -W. Thus, the internal energy will increase if the work done is negative and vice versa.