Thermodynamic Properties: Overview, Features, State of a System

In science, thermodynamic properties are characteristics used to describe a physical system. They refer to qualities such as heat, pressure, and temperature, which affect phenomena from the Earth’s atmosphere to the rates at which chemical reactions occur.

Thermodynamic Properties measure the various factors that influence this process between two or more objects. Engineers use these to design better, more efficient machines. The thermodynamic properties are classified into types namely, intensive and extensive properties. In this article, we will provide you with detailed information about thermodynamic properties. Scroll down to learn more!

What are Thermodynamic Properties?

A thermodynamic property is a characteristic or a particularity that allows the changes of the work substance, that is to say, changes of energy.

The thermodynamic properties can be classified as intensive and extensive. They are intensive those that do not depend on the amount of matter of the system (pressure, temperature). Extensive ones depend on the size of the system (mass, volume).

Definition of Thermodynamic Properties

Thermodynamic properties are defined as characteristic features of a system capable of specifying the system’s state. 

Thermodynamic Properties

The two types of thermodynamic properties are intensive properties and extensive properties. 

1. Intensive properties: The properties which do not depend upon the quantity of matter present in the system or the size of the system are called intensive properties. Pressure, temperature, density, specific heat, surface tension, refractive index, viscosity, melting point, boiling point, volume per mole, concentration, etc., are examples of intensive properties of the system. 
2. Extensive properties: The properties whose magnitude depends upon the quantity of matter present in the system are called extensive properties.

The extensive property is an additive property of the system. For a heterogeneous system consisting of several phases, the extensive property value will be equal to the sum of contributions from several phases—examples: Mass, volume, internal energy, enthalpy, entropy, etc.

The following are some salient features of these properties:

1. In a system having two or more substances, the extensive property will depend not only on the independent variables but also on the number of moles of different components present in it.
2. If an extensive property is expressed per mole or per gram, it becomes intensive property. For example, mass and volume are extensive properties, but density (mass per unit volume) and specific volume (volume per unit mass) are intensive properties.
3. The product, sum, and the ratio of intensive properties are also intensive properties. Let \(X\) and \(Y\) be two intensive properties, then \((X+Y) ; X Y: \frac{X}{Y} ; \frac{\partial X}{\partial Y}\) are intensive properties
4. Let \(X\) and \(Y\) be the two extensive properties, then
   (a) \((X+Y)\) will also be an extensive variable,
   (b) \(\frac{X}{Y}\) and \(\frac{\partial X}{\partial Y}\) will be intensive variables.

When the total mass, temperature, volume, number of moles, and composition have definite values, the system is said to be in a definite state. When there is any change in any one of these properties, it is said that the system has undergone a change of state.

State of a System

The system is said to be in a certain state when its macroscopic properties have definite values. It is defined in terms of its state function, such as \(P, V, T\), etc.

If any one of the state functions is changed, the state of that system is said to be changed.

The condition of the existence of a system when its macroscopic properties have definite values is known as the state of the system.

For example: at \({\text{1}}\,{\text{atm}}\) pressure \({H_2}O\) is

a) Solid below \(O^{\circ} \mathrm{C}\)
b) The liquid between \(O^{\circ} \mathrm{C}-100^{\circ} \mathrm{C}\) and
c) gas above \(100^{\circ} \mathrm{C}\).

State Variables

Since the state of a system changes with the change in any of the macroscopic properties, the latter are called state variables. As mentioned earlier, whenever a system changes from one state to another state, there is always a change in one or more of the macroscopic properties. Thus, the macroscopic properties whose values change the state of the system are called state variables, thermodynamic variables, or thermodynamic parameters.

Of all the macroscopic properties (state variables), the four most common which are sufficient to define the state of a system are composition\(\left( C \right)\), pressure\(\left( P \right)\), volume\(\left( V \right)\), and temperature\(\left( T \right)\). If these properties are fixed, all other physical properties of the system are automatically fixed.

Further, if the system is homogeneous and consists of a single substance as in a pure gas, the composition is fixed as in such cases, the composition is always \({\text{100% }}\). Hence, in such cases, the state of the system depends only upon pressure, volume, and temperature. Further, the system’s pressure, volume, and temperature are interrelated in the equation of state. Thus, for one mole of pure gas, the equation of state is \(PV = RT\).

Where \(R\) is a gas constant, if all the three variables (\(P, V\) and \(T\)), two variables (generally \(P\) and \(T\)) are specified, the value of the third \(\left( {\text{V}} \right)\) is fixed automatically. It can be calculated from the equation of state. The variables (\(P\) and \(T\)) which must be necessarily specified to define the state of a system are designated as independent state variables. In contrast, the remaining variables (generally \(V\)) whose value depends upon \(P\) and \(T\) values are called dependent state variables.

Thus, the thermodynamic state of a system consisting of a single gaseous substance (simple homogeneous system) may be completely defined by specifying any two of the three variables, i.e. temperature, pressure, and volume. For example, the state of water is completely defined by fixing the value of any two of the three variables \(P, V\), and \(T\).

Variables Used in Describing State of Thermodynamic System

Following are the state variables that are commonly used in describing the state of the thermodynamics systems:

1. Pressure \(\left( P \right)\)
2. Temperature \(\left( T \right)\)
3. Volume \(\left( V \right)\)
4. Internal energy \(\left( U \right)\)
5. Enthalpy \(\left( H \right)\)
6. Entropy \(\left( S \right)\)
7. energy \(\left( G \right)\)
8. Number of moles \(\left( n \right)\)

Path Function

Path functions are properties or quantities whose values depend on the transition of a system from the initial state to the final state. The two most common path functions are heat and work.

For path functions, the path from an initial state to the final state is crucial. Each part or segment of the path to the final state is necessary to take into account. For example, a person may decide to hike up a \({\text{500 ft}}\) mountain. Regardless of what path the person takes, the starting place and the final place on top of the mountain will remain constant. The person may decide to go straight up to the mountain or spiral around to the top of the mountain. There are many different ways to get to the final state, but the final form will remain the same.

Two important examples of a path function are heat and work. These two functions are dependent on how the thermodynamic system changes from the initial state to the final state. These two functions are introduced by the equation \(\Delta U\), which represents the change in the internal energy of a system.

\(\Delta U=q+w\)

\(U\) is a state function (it does not depend on the system’s initial to the final state).

Thermodynamic Properties of Refrigerant

A refrigerator may be defined as a device that operates in a thermodynamic cycle and transfers a certain amount of heat from a body at a lower temperature to a higher temperature by consuming certain external work. Domestic refrigerators and room air conditioners are examples. In a refrigerator, the required output is the heat extracted from the low-temperature body.

Thermodynamic Properties of Ammonia (\(R\,717\)) in Refrigerant

A refrigerator may be defined as a device that operates in a thermodynamic cycle and transfers a certain amount of heat from a body at a lower temperature to a body at a higher temperature by consuming a certain amount of external work. Domestic refrigerators and room air conditioners are examples. In a refrigerator, the required output is the heat extracted from the low-temperature body.

Ammonia has the highest refrigerating capacity per pound of any refrigerant and several other excellent thermal properties that make it popular for many refrigeration applications despite its being toxic, explosive, and flammable within certain conditions. Ammonia is used as a refrigerant prominently in the refrigeration systems of the food industry like dairies, ice cream plants, frozen food production plants, cold storage warehouses, processors of fish, poultry, and meat of other applications.

Thermodynamic Properties are Point Functions

1. Point function is a value is depending on its initial state and final state of the thermodynamics process. The point function is not dependent on the area of the graph. 
2. Point function depends on the point of the thermodynamics process. 
3. The point function has the exact and perfect differential, so two points difference is calculated in the point function. 
4. Point function is a thermodynamic property of the system. All thermodynamics property is to be the point function.
5. The thermodynamics cycle does not change in value because, in the cycle, the first and last points are the same, so the thermodynamics cycle point function change is zero.

Summary

Thermodynamic property is essential to describe the state of a system. Properties like temperature are intensive because they are independent of a given system’s size, unlike volume, which varies with the object’s size. Engineers and chemists use thermodynamic properties to build engines and plan chemical reactions that maximize heat energy efficiency.

In this article, we learned about the properties of thermodynamics, state variables, path function, and thermodynamic properties of the refrigerant.

FAQs on Thermodynamic Properties

Q.1. What are thermochemical properties?
Ans: The thermochemical equations can determine the energy, entropy, osmotic pressure, and water activity in seawater.

Q.2. What are the three properties that describe the thermodynamic state of a system?
Ans: The thermodynamic state is defined by specifying values of a set of measurable properties sufficient to determine all other properties. For fluid systems, typical properties are pressure, volume, and temperature. More complex systems may require the specification of more unusual properties.

Q.3. How are thermodynamic properties classified?
Ans: Properties are classified as either intensive or extensive. Properties are intensive if independent of the mass is present and extensive if a function of the mass is present. Properties such as pressure, temperature, and density are intensive, whereas volume and mass are extensive.

Q.4. What are the thermodynamic properties? Write its type.
Ans: A thermodynamic property is a characteristic or a particularity that allows the changes of the work substance, that is to say, changes of energy. Thermodynamic properties are divided into two broad types: Intensive properties and extensive properties. An extensive property is any property that depends on the system’s size (or extent) under consideration. An intensive property is any property that can exist at a point in space.

Q.5. Is quality a thermodynamic property?
Ans: Yes, it is a thermodynamic property. Quality, x, is the mass fraction of vapour in a liquid/vapour mixture. It is directly related to heat input and is sometimes called the thermodynamic quality.

Q.6. What are the thermodynamic properties of refrigerants?
Ans: A refrigerator may be defined as a device that operates in a thermodynamic cycle and transfers a certain amount of heat from a body at a lower temperature to a higher temperature by consuming certain external work. Domestic refrigerators and room air conditioners are examples. In a refrigerator, the required output is the heat extracted from the low-temperature body.

Q.7. What are extensive properties?
Ans: The properties whose magnitude depends upon the quantity of matter present in the system are called extensive properties.

Q.8. Define Path Functions.
Ans: Path functions are properties or quantities whose values depend on the transition of a system from the initial state to the final state. The two most common path functions are heat and work.

Learn About First Law of Thermodynamics

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