Physics

# Difference between First Law of Thermodynamics and Second Law of Thermodynamics

The First Law of Thermodynamics is related to the conservation of energy, while the Second Law of Thermodynamics argues that some of the processes of thermodynamics are inadmissible and do not fully follow the First Law of Thermodynamics. The main difference between the first law of thermodynamics and the second law of thermodynamics is that the first law of thermodynamics discussed that energy cannot be created or destroyed, but it can change its shape, while according to the second law From thermodynamics, the entropy of a system always increases.

## Key differences

Below are the essential points to differentiate between the first and second law of thermodynamics:

• The first law of thermodynamics refers to energy which states that energy can never be generated or destroyed, but can only change in different ways, while the second law of thermodynamics is the law that states that the entropy of a system it never decreases but always increases.
• According to the First Law of Thermodynamics ‘Energy cannot be created or destroyed, it can only be transformed from one form to another’. According to the Second Law of Thermodynamics , it does not violate the first law, but says that the energy that is transformed from one state to another is not always useful and 100% as it is taken. Therefore, it can be stated that “the entropy (degree of disorders) of an isolated system never decreases but always increases”.
• ΔE = q + w is the equation of the first law of thermodynamics that is used to calculate a value if two other quantities are known in reverse. The second law of thermodynamics states that The total change in entropy is equal to the sum of the change in entropy of the system and its environment
• The example of the first law of thermodynamics is photosynthesis in which plants convert solar energy into chemical energy, that is, glucose, while a heater in the room is an example of the second law of thermodynamics that uses the electrical energy and provides heat to the room, while in return the room cannot provide the same energy to the heater.
• The first law of thermodynamics can be expressed as ΔE = Q + W , it is used for the calculation of the value, if two quantities are known, while the second law of thermodynamics can be expressed as ΔS = ΔS (system) + ΔS (environment)> 0 .
• The first law of thermodynamics is also called the “law of conservation of energy”, on the other hand, the second law of thermodynamics is also called the “law of increased entropy.”
• The equation of the first law of thermodynamics states that, the change in the internal energy of a system is equal to the total heat that flows into the system and the environment does the work in the system. On the other hand, the Second Law of Thermodynamics states that the total change in the system can be obtained by the sum of the change in entropy of the system and the environment.
• The expressions imply that the change in internal energy of a system is equal to the sum of the heat flow in the system and the work done on the system by the First Law environment. In the Second Law, the total change in the Entropy is the sum of the change in the entropy of the system and the environment that will increase for any real process and cannot be less than 0.

## First law of thermodynamics vs second law of thermodynamics

The word ‘thermodynamics’ is derived from a Greek word, where ‘Thermo’ means heat and ‘dynamic’ means power. So, it is the study of energy that exists in different forms such as heat, light, electrical and chemical energy. There are four different laws of thermodynamics, that is, zero law, first law, second law, and third law.

But the most important thing is the first and second laws of thermodynamics. The first law of thermodynamics argued that energy cannot be generated or destroyed, but can only change its shape, while the second law of thermodynamics states that the entropy of a system never decreases but always increases.

When discussing these laws, two terms are very important, namely system and environment. Any element or group of elements that we are dealing with that may be small like a cell or large like an ecosystem is known as a system. Everything present around the system is known as its environment.

The word ” thermodynamics ” is derived from the Greek words, where “thermo” means heat and “dynamic” means power. So thermodynamics is the study of energy that exists in various forms, such as light, heat, electrical and chemical energy.

Thermodynamics is a very vital part of physics and its related field such as chemistry, materials science, environmental science, etc. Meanwhile, “Law” means the system of rules. Therefore, the laws of thermodynamics deal with one of the forms of energy which is heat, and its behavior in different circumstances corresponds to mechanical work.

Although we know that there are four laws of thermodynamics, starting with the zero law, the first law, the second law and the third law. But the most used are the first and the second law, therefore, in this content, we will discuss and differentiate the first and the second law.

## What is the first law of thermodynamics?

The first law of thermodynamics, which is also called the law of conservation of energy, looks at the total energy in the universe. It states that this total amount of energy remains the same. According to this law, energy can change shape, but it cannot be created or destroyed.

The first law of thermodynamics states that ” energy cannot be created or destroyed “, it can only be transformed from one state to another. This is also known as the law of conservation.

There are many examples to explain the above statement, such as an electric light bulb, which uses electrical energy and is converted into light and heat.

All types of machines and engines use one type of fuel or another to get the job done and get different results. Even living organisms eat food that is digested and provides energy to perform different activities.

ΔE = Q + W

It can be expressed by the simple equation as ΔE, which is the change in the internal energy of a system is equal to the sum of heat (Q) that flows through the limits of the environment and the work is done (W) in the system by the environment. But suppose that if the heat flow were from the system, then the ‘Q’ would be negative, similarly if the work was done by the system, then the ‘W’ would also be negative.

So we can say that the whole process is based on two factors, which are heat and work, and a slight change in these will result in the change in the internal energy of a system. But as we all know, this process is not so spontaneous and it is not always applicable, as energy never spontaneously flows from a lower temperature to a higher one.

## Examples

• During photosynthesis, plants use sunlight, that is, solar energy, and convert it into chemical energy, that is, glucose.
• A lightened electric light bulb converts electrical energy into light energy.
• When we walk, breathe or run, etc. After a meal, we are converting the chemical energy in our food into kinetic energy.

## Equation

ΔE = q + w His equation states that the change in internal energy of a system is equal to the total heat that flows into the system and the environment does the work in the system. It can be used to calculate a value if the other two quantities are known.

## What is the Second Law of Thermodynamics ?

According to this law of thermodynamics, the entropy of a system never decreases but always increases. Entropy is the disorder or degree of randomness in a system. The first law states that energy can never be generated or destroyed, which means that energy can be recycled over and over again. But, according to the Kelvin-Plancks statement , there is no system that can convert energy into different forms with 100% efficiency. It means that a certain amount of energy is always wasted uselessly in a process. So the entropy of a system always increases. The Second Law of Thermodynamics also explains that the transformation of energy takes place only in one particular direction, which was not made clear in the First Law of Thermodynamics.

There are several ways to express the second law of thermodynamics, but before that we need to understand why the second law was introduced. We believe that in the actual process of everyday life, the first law of thermodynamics should satisfy, but is not mandatory.

For example, consider an electric light bulb in a room that will cover the electric energy in heat (thermal) and light energy and the room will light up, but the opposite is not possible, if we provide the same amount of light and heat for the light bulb, it will will convert into electrical energy. Although this explanation is not contrary to the first law of thermodynamics, it is not actually possible either.

According to the Kelvin-Plancks statement “It is impossible for any device to run in a cycle, receive heat from a single reservoir and convert it 100% into work, that is, there is no heat engine that has a thermal efficiency of 100% “.

Clausius even said that “it is impossible to build a device that runs in a cycle and transfers heat from a low-temperature reservoir to a high-temperature reservoir in the absence of external work.”

So from the above statement it is clear that the Second Law of Thermodynamics explains the way energy transformation takes place only in one particular direction, which is not clarified in the first law of thermodynamics.

The Second Law of Thermodynamics also known as the Law of Increased Entropy, which says that over time the entropy or degree of disruption in a system will always increase. Let’s take an example, this is why we make more mistakes, after starting any job with all the schedules as the job progresses. So, with increasing time, disorders or disorganization also increase.

This phenomenon is applicable in all systems, that with the use of useful energy, unusable energy will be given away.

ΔS = ΔS (system) + ΔS (surrounding)> 0

As described above, the delS that are the total change in entropy is the sum of the change in entropy of the system and the environment that will increase for any real process and cannot be less than 0.

## Examples

• An electric bulb can convert electrical energy into light energy, but the reverse process is not possible, that if we provide the same amount of heat and light to the bulb, it converts it into electrical energy.
• A heater in the room uses electrical energy and provides heat to the room, while in return the room cannot provide the same energy to the heater.

## Equation

ΔS = ΔS system + ΔS environment This is the equation used to measure the overall entropy change of the system.

## Conclution

In this article, we discuss Thermodynamics, which is not limited to physics or machinery such as refrigerators, cars, washing machines, but this concept is applicable to everyone’s daily work. Although here we distinguish the two most confusing Laws of Thermodynamics, since we know that there are two more, which are easy to understand and not so contradictory. According to the discussion above, it is summarized that according to the first law of thermodynamics, energy can never be generated or destroyed, it can only be converted into different forms, but it cannot explain the direction of the transformation of energy that it was clarified by the second law of thermodynamics which states that the entropy of a system always increases.