Tag: entropy

Introduction

Everything in the universe consists of tiny particles called molecules, which are classified based on the distance and the attractive force between their constituents. Different substances have distinct properties such as mass, temperature, density, volume, pressure, etc. 

The process of transfer of heat is achieved through three different processes in matter, namely, conduction, convection, and radiation. It is studied under thermodynamics, which deals with thermal energy and its relationship to heat, work, temperature, energy, entropy, and other physical properties of matter. 

Isotherms and adiabats

Thermodynamic system

A thermodynamic system is defined as a collection of matter confined within specific boundaries. Within the system, transformations can take place internally. At the same time, interaction with the outside world can occur through the boundaries, which can have a definite permeability. 

Based on the type of the boundary of the thermodynamic system, it can be classified into three categories: isolated system, closed system, and open system. 

• In an isolated system, no energy or matter is exchanged across its boundaries, and no work is performed. An example is items packed in a vacuum bag.
• A closed system allows for energy transformation, but matter cannot cross its boundaries, as seen in a cylinder closed by a valve. 
• And finally, an open system allows for the free exchange of energy and matter across its boundaries, such as a pool filled with water.

Thermodynamic processes

Thermodynamic processes involve an energy transfer between two systems or between systems and their surroundings, resulting in changes in volume, pressure, or temperature. Depending on the type of process, the process can change the energy of the system and perform some work on or by the system.

To classify thermodynamic processes, we look at how they are performed and what conditions they are performed in. 

• An isothermal process is one where the temperature of the system remains constant while energy is exchanged in or out.
• An isobaric process keeps the pressure constant.
• An isochoric process occurs when there is no change in the volume of the system.
• Finally, in an adiabatic process, no heat is exchanged by the systems. We’ll discuss adiabatic processes in detail here.

What is an adiabatic process?

An adiabatic process refers to a thermodynamic process in which, no heat energy is exchanged between the system and the surroundings. To be considered adiabatic, the system must satisfy two conditions.

1. It must be completely isolated. 
2. The process must occur over a short enough time frame, which makes it impossible for heat transfer to take place. 

Work done in adiabatic process

We start with a cylinder with walls made up of an insulating material. We assume that it has a frictionless piston attached to it also made up of an insulating material, effectively preventing heat from escaping. 

Reversible adiabatic process

An adiabatic process is considered reversible if the system can go back to its original state with no alterations. However, this can’t be achieved practically since a reversible adiabatic process does not really exist in nature. But theoretically, such a process is known as an isentropic process and one example of such a process is the adiabatic expansion of a real gas.

Irreversible adiabatic process

If the system cannot return to its original state after the process has occurred, the process is termed irreversible and is accompanied by a change in the entropy of the system. One example would be heat transfer.

Application of adiabatic process

Adiabatic processes occur in the following scenarios:

1. The principle is used in refrigerators.
2. Some processes in a thermal engine are adiabatic in nature. 
3. Compressors and turbines also work on adiabatic principles. 
4. Igloos and thermos flasks are isolated systems and they utilise adiabatic principles.
5. Quantum harmonic oscillators work adiabatically.

Carnot cycle

Summary

This tutorial covered the topic of thermodynamic systems and processes, including the work done in adiabatic processes. The discussion also included the differences between reversible and irreversible adiabatic processes and the various applications of adiabatic processes.

Frequently Asked Questions

1. Give some examples for all thermodynamic processes.

There are four types of thermodynamic processes: isothermal, adiabatic, isobaric, and isochoric. Some examples of these processes include boiling water, refrigeration, the Carnot engine, heat pumps, the freezing of water into ice, pressure cooking, and vertical atmospheric airflow.

2. Differentiate isothermal and adiabatic processes.

3. What is the specific heat capacity?

The specific heat capacity refers to the amount of energy that must be supplied to one mole of a substance to increase its temperature by one degree.

4. What do adiabatic compression and expansion do?

Adiabatic compression leads to an increase in system temperature and adiabatic expansion causes a decrease in temperature.

5. What is the first law of thermodynamics?

The first law relates the internal energy of the system with the heat exchange the work done. According to the first law, internal energy is the difference of the latter two quantities.

Also Read: Adiabatic Processes Derivation

Introduction

The whole universe is composed of two parts; system and surroundings. There occurs an exchange of heat between the system and the surroundings. Thermodynamics tells us about the exchange of heat, different forms of energy, and the transformation of energy into work. It also explains some other properties of the system like temperature, pressure, density, enthalpy, entropy, etc.

Define Thermodynamics

Thermodynamics is a topic that derives the relationship between heat, energy, work, and temperature. According to thermodynamics, if the system does the work then its value will be negative and when work is done on the system its value will be positive.

Difference between Thermodynamics and Statistical Mechanics

Define System and Surroundings

System: The part of the universe in which all the matter remains is known as a system. 

Surroundings: The other part of the universe outside the system is known as the surroundings. The system and surroundings are divided by a boundary.

Classification of the system:

1. Open system: It has the capacity to exchange both energy and matter with the surroundings. In an open system, both the temperature T and pressure P are constant. For example, the human body.
2. Closed system: This system only exchanges energy with the surroundings. The entropy of a closed system is always constant. For example, water boils using a closed lid.
3. Isolated system: It exchanges neither matter nor energy with the surroundings. For example, a thermos flask is an example of an isolated system. 

Different types of processes in thermodynamics

• Isothermal process: In this process, the temperature (T) of the system is always constant.

1. Isochoric process: Here, the volume (V) of the system is always constant.
2. Isobaric process: In this process, the pressure (P) of the system remains constant.
3. Adiabatic process: In this process, the change in heat (Q) with the surroundings is zero.

Properties of thermodynamics

1. Intensive properties: These properties don’t change with the change in the amount of matter. For example boiling point, melting point, density, etc.
2. Extensive properties: These properties highly depend on the amount of matter in the system. For example mass, volume, etc.

Functions in thermodynamics

1. State functions: These functions change with the change in the state of a system. For example Enthalpy (H), internal energy (U), entropy(S), and density (d). 
2. Path functions: Heat (Q) and work (W) don’t depend on the state of a system, but rather depend on the path of a system. They are called path functions.

Define Enthalpy and Entropy

Enthalpy (H): It is a property of thermodynamics that indicates the overall heat capacity of a system. It is expressed by the sum of the system’s internal energy and the product of the pressure and volume of the system. 

H = U + PV

Depending on the symbol before the value of enthalpy, any reaction can be classified into two parts.

• Exothermic reaction: The reaction is called exothermic when heat is generated during a reaction. The value of enthalpy in an exothermic reaction is always negative.
• Endothermic reaction: When the system absorbs energy from the surroundings to execute a reaction is called an endothermic reaction.  The value of enthalpy in an exothermic reaction is always positive.

Entropy (S): It measures the extent of disorderness of a system. For a spontaneous reaction, entropy S is always negative and for a non-spontaneous reaction, entropy S is always positive.

Thermodynamic potential

Thermodynamic potentials are used to define a particular state of the system. They are internal energy (U), enthalpy (H), Gibbs free energy (G), and Helmholtz free energy (F).

Laws of thermodynamics

• Zeroth law: This law states: “if two bodies A and B are each in thermal equilibrium with some third body C, then they are also in equilibrium with each other.”
• First law: This law states:  “Energy can neither be destroyed nor be created, it can only be transferred from one form to another”. It is also called the “Law of conservation of energy.”

ΔQ = ΔU + W

ΔQ= Change in heat of a system.

ΔU = Change in internal energy of a system.

W = Work done

• Second law: This law states: “any spontaneously occurring process will always lead to an escalation in the entropy (S) of the universe.”

\[\Delta {S_{Total}} = {\rm{ }}\Delta {S_{system}} + {\rm{ }}\Delta {S_{surroundings}} > {\rm{ }}0\]

• Third law: This law states: “the entropy of a system approaches a constant value as the temperature approaches absolute zero.”

\[{S_{T = 0}} = 0\]

Daily life examples of thermodynamics

1. Human bodies sweat, producing heat from the body.
2. Melting of ice cubes.
3. Like A thermodynamic system, the human body exchanges mass and energy with the surroundings.

Summary

A type of heat energy that connects with other types of energy is called thermodynamics. Heat or work are two ways that energy is changed or exchanged. In thermodynamics, there are four processes. They are isothermal, adiabatic, isobaric, and isochoric. Thermodynamics explains many important properties of the system. Energy is the dominant focus of thermodynamics which is how it is used and transforms from one state to another. Thermodynamics frequently includes using heat to generate work like in the engines of automobiles and generating work to transfer heat like in the refrigerator.

Frequently Asked Questions 

1. Why does thermodynamics emphasize energy?

Ans: The first law of thermodynamics defines that the total energy of the system is always conserved. Neither energy can be created nor destroyed. It is only capable to change from one type to another. Like, in the combustion of fuel the chemical energy is transformed into thermal energy.

2. Why is it referred to as free energy?

Ans: Because it is readily accessible at all times, Gibb’s free energy is known as free energy. If necessary, the reaction can obtain this energy without exerting any effort.  Enthalpy (H) and also the product of the system’s temperature (T) and entropy(S) are added to determine the change in Gibbs free energy (G).

G = H +TS

3. What are the drawbacks of thermodynamics?

Ans: Thermodynamics can’t explain any properties of the system quantitatively. It doesn’t include the direction of the flow of heat. It can’t tell anything about the spontaneity of any reaction. These are the drawbacks of thermodynamics.