laws of Thermodynamics | What is the 2nd law of Thermodynamics

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Table of Contents

1 laws of thermodynamics

2 what is zeroth law of thermodynamics

5 first law of thermodynamics

4 what is the 2nd law of thermodynamics

laws of Thermodynamics :

You are familiar with the sensations of heat and cold in your daily life. You feel warmth when you rub your hands together. You would assume that the cause of heat in this phenomenon is mechanical work. This shows that there is some relation between mechanical work and thermal effect. The transfer of thermal energy between objects at different temperatures is the subject matter of thermodynamics, which is the science of phenomena based on experiences. For a quantitative description of thermal phenomena, it is necessary to define heat, heat and internal energy.

The laws of thermodynamics describe the relationship between heat flow, work done, and internal energy in a system.

In this lesson you will get knowledge about three laws of thermodynamics - zero order law, first and second laws of thermodynamics. These rules are based on experience and do not require any proof.

The zero order laws of thermodynamics, the first and second laws introduce the concepts of temperature, internal energy and entropy respectively. The first law is actually the principle of conservation of energy for a thermodynamic system. The second law deals with the mutual transformation of work and heat. You will also learn that the Carnot engine has the highest efficiency in converting heat energy into work.

Three laws of Thermodynamics_

 1 Zero order law of thermodynamics

 2 First Law of Thermodynamics

 3 Second law of thermodynamics

What is Zeroth law of Thermodynamics :

Let there be three blocks of metal A, B, C. Block A is in thermal equilibrium with block B and block A is also in thermal equilibrium with block C. This means that the temperature of block A is same as that of block B and C. From this it can be concluded that the blocks B and C have the same temperature. We express this magnitude in a nutshell as the rule of zero order as follows.

If two bodies or systems A and B are in different thermal equilibrium with a third body or system C, then they will also be in thermal equilibrium with each other.

First Law of Thermodynamics :

Now you know that the zero order law of thermodynamics tells us about the thermal equilibrium between different systems characterized by having the same temperature. However, this rule does not give any information about the abnormal state.

 Let us Consider two Examples-

1- The two systems are kept in thermal contact through different thermal 

2- Mechanical friction between two bodies.

In both these situations, their temperatures change but it cannot be explained by the zero order law, the first law of thermodynamics was presupposed to explain these processes.

The first law of thermodynamics is actually the principle of conservation of energy for a thermodynamic system. According to this, the change in internal energy in a thermodynamic process is equal to the sum of the heat given to it and the work done on it.

Let a system be given a quantity Q. – W is the work done on the object, then the increase in internal energy according to the first law of thermodynamics

 U = Q – W

It is the mathematical form of the first law of thermodynamics. Here Q, U and W are in SI units. The first law of thermodynamics can also be written as follows.

 Q = U + W

The symbols for Q, U and W are as per the following convention-

Work done (AW) by a body is taken as positive and work done on a body is taken as negative. Work is taken positive in expansion of the system and negative in compression. The work done does not depend on the initial and final thermodynamic states, it depends on the path followed for the change.

The heat gained by the system is taken as positive and the heat lost by it as negative.

The increase in internal energy is taken as positive and the decrease in negative.

If a system is moved from position 1 to position 2, it is found that Q and W depend on the path of change of state. However, the value of (ΔQ – W) remains the same for all phase transition paths. So we can say that the internal energy U does not depend on the path of thermodynamic change of a system.

Limitations of the first law of Thermodynamics:

The first law of thermodynamics emphasizes the equivalence of heat and other forms of energy. It is only on the basis of this equivalence that our activities are possible. The electrical energy that lights our homes, operates machines, runs trains comes from the heat that comes from burning fossil fuels or nuclear fuel. In one sense, this rule is universal. This explains the drop in temperature (the adiabatic loss rate) as altitude increases. Their applications in flow processes and chemical reactions are also quite interesting. However, consider the following processes.

You know that heat always flows from a hotter substance to a colder one, but the first law of thermodynamics is unable to explain why heat cannot flow from a cooler object to a hotter object. This means that this law does not give any indication about the direction of heat flow.

You know that when a bullet hits a target, the kinetic energy of the bullet gets converted into heat. This law does not explain why the heat generated by the bullet hitting the target is not converted into the kinetic energy of the bullet so that the bullet flies away. This means that this law is incapable of giving knowledge of the conditions in which heat can be converted into work.

Apart from this, another obvious limitation of this is that this law does not know the extent to which heat can be converted into work, as well as this law does not indicate to what extent heat can be converted into work

Second law of Thermodynamics :

You know that the first law of thermodynamics has inherent limitations in terms of heat flow, and the ability to transform (that is, the ability to convert heat into work). Thus an idea may arise in your mind whether heat can be converted into work. What are the terms of conversion? The answer to all these questions lies in the concept of the second law of thermodynamics. There are many statements of the second law of thermodynamics. However, you will study about Kelvin Plank's and Classius' statement of the second law of thermodynamics.

Calvin-Planck Statement:

It is based on experience about the capabilities of heat engines. The heat engine is discussed in the next section. In a heat engine, the working material takes heat from the source (hot material) and after converting some of it into work, gives the rest to the heat sink. (cold object or environment). There is no engine that can convert all the heat into work without providing some heat to the sink. On the basis of these observations, Kelvin and Planck made this statement about the second law of thermodynamics.

It is impossible for a system to absorb heat from a source at a constant temperature and convert its entire amount into work.

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Clausius' second law of thermodynamics:

It is based on the function of the refrigerator. Refrigerator heat is an engine that works in the opposite direction.

When it is acted upon, it transfers heat from a relatively cold object to a relatively hot object. Here the concept of external work done on the body is important. To do this external work, energy supply by an external source is necessary, on the basis of these facts, Clausius gave this statement about the second law of thermodynamics.

It is impossible in a process to convert heat from a relatively cold object to a hotter object without external work being done.

Therefore, the role of the second law of thermodynamics is unmatched in practical applications such as in heat engines and refrigerators.The first law of thermodynamics is related to the conservation of matter and energy.

According to this, energy can neither be created nor destroyed, but it can change from one form to another. Most of the energy is used in the metabolism, movement and other activities of living organisms.

* According to the second law of thermodynamics, during each energy conversion, some amount of useful energy is degraded as unusable waste.

* The cells of living organisms constantly require energy which is mainly available in the form of adenosine triphosphate and some of the energy is converted into unusable heat during the same time. Since heat energy cannot do any useful work, it is necessary to supply energy to the biological system from outside to compensate for this inevitable energy loss.

* If all the people of the world become vegetarian, then algae will disappear from many food chains, which will deform the food web and cause ecological crisis 

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