Second law of thermodynamics:

1. Heat cannot by itself pass from a cold to a hot body.

2. All spontaneous processes are to some extent irreversible and are accompanied by degradation of energy.

3. It is impossible to construct a heat engine that operates continuously in a cycle to produce no effect other than conversion of heat supplied completely into work. This is called Kelvin – Planck statement.

4. It is impossible to construct a heat pump (reverse heat engine) that operates continuously to produce no effect other than transfer of heat from low temperature body to a high temperature body.

Heat capacity

Heat capacity:

Heat capacity of a substance is defined as the heat transfer necessary to bring about a change in the temperature of unit amount of substance by one degree centigrade. Since it is heat transfer which is a path function, it depends upon the way heating is done. For example gases can be heated to increase the temperature by two different methods. The unit quantity of gas taken in container with rigid wall, when heated its volume remains constant. Another method is to have the wall which is flexible. If the piston is movable in the piston and cylinder arrangement, gas when heated pushes piston and pressure will be constant. Even if we take unit amount of gas in both these heating methods, it is observed the heat transfer is not the same.

Thermodynamics Process

Thermodynamic process:

A system in thermodynamic equilibrium is disturbed by imposing some driving force; it undergoes changes to attain a state of new equilibrium. Whatever is happening to the system between these two equilibrium state is called a process. It may be represented by a path which is the locus all the states in between on a p-V diagram as shown in the figure above.

For a system of gas in piston and cylinder arrangement which is in equilibrium, altering pressure on the piston may be driving force which triggers a process shown above in which the volume decreases and pressure increases. This happens until the increasing pressure of the gas equalizes that of the surroundings. If we locate the values of all intermediate states, we get the path on a p-V diagram.

Equilibriums of Thermodynamics

Equilibrium state:

A system is said to be in thermodynamic equilibrium if it satisfies the condition for thermal equilibrium, mechanical equilibrium and also chemical equilibrium. If it is in equilibrium, there are no changes occurring or there is no process taking place.

Thermal equilibrium:

There should not be any temperature difference between different regions or locations within the system. If there are, then there is no way a process of heat transfer does not take place. Uniformity of temperature throughout the system is the requirement for a system to be in thermal equilibrium.

Surroundings and the system may be at different temperatures and still system may be in thermal equilibrium.

Mechanical equilibrium:

There should not be any pressure difference between different regions or locations within the system. If there are, then there is no way a process of work transfer does not take place. Uniformity of pressure throughout the system is the requirement for a system to be in mechanical equilibrium.

Surroundings and the system may be at pressures and still system may be in mechanical equilibrium.

Chemical equilibrium:

There should not be any chemical reaction taking place anywhere in the system, then it is said to be in chemical equilibrium. Uniformity of chemical potential throughout the system is the requirement for a system to be in chemical equilibrium.

Surroundings and the system may have different chemical potential and still system may be in chemical equilibrium.

Basic of Thermodynamics

Introduction:

Thermodynamics deals with heat inter-action and work inter-action with the substances called systems. Work and heat are forms of energy. Transfer of heat or work to a substance brings about certain changes in the substance and whatever change happens is called a process. Thermo means heat. Since work is also a form of energy, thermo is taken to mean heat and work. Dynamics refers to the changes that occur as a result of heat or work transfer.

Biological systems are capable doing work. For example, micro-organism is capable swimming in the body fluid of its host. It needs to do the work. Where does energy for doing this work come from? It is the metabolic activity that converts some form of energy (Nutrition that it takes form host is a form of chemical energy) into work. It is important then to understand how this happens so that we can exploit this to our engineering benefit.

In thermodynamics we have work transfer, heat transfer and then we have a system for interaction which undergoes a process. Let us look at these basic terms.

System:

We need to fix our focus of attention in order to understand heat and work interaction. The body or assemblage or the space on which our attention is focused is called system. The system may be having real or imaginary boundaries across which the interaction occurs. The boundary may be rigid and sometimes take different shapes at different times. If the system has imaginary boundary then we must properly formulate the idea of system in our mind.





Surroundings:

Every thing else apart from system constitutes surroundings. The idea of surroundings gets formulated the moment we define system. System and surroundings together form what is known as universe.

Closed system:

If the system has a boundary through which mass or material cannot be transferred, but only energy can be transferred is called closed system. In an actual system, there may not be energy transfer. What is essential for the system to be closed is the inability of the boundary to transfer mass only.

Open system:

If the system has a boundary through which both energy and mass can transfer, then it is called open system.

Properties:

Variables such as pressure, temperature, volume and mass are properties. A system will have a single set of all these values.


Intensive properties:

The properties that are independent of amount contained in the system are called extensive properties. For example, take temperature. We can have a substance with varying amount but still same temperature. Density is another example of intensive property because density of water is same no matter how much is the water. Other intensive properties are pressure, viscosity, surface tension.






Extensive properties:

The properties that depend upon amount contained in the system are called extensive properties. Mass depends upon how much substance a system has in it therefore mass is an extensive property.

State:

It is defined as condition of a system in which there are one set of values for all its properties. The properties that define the state of a system are called state variables. There is certain minimum number of intensive properties that requires to be specified in order to define the state of a system and this number is uniquely related to the kind of system. This relation is phase rule which we shall discuss little later.

Process:
The changes that occur in the system in moving the system from one state to the other is called a process. During a process the values of some or all state variables change. The process may be accompanied by heat or work interaction with the system.

Heat:

It is a form of energy that exists only in transit. This transit occurs between two points which differ in temperature. Since it exists only in transit, it should be accompanied by changes that occur in the system. The moment this energy cease to move, it appears as internal energy. We shall discuss internal energy when we deal with I law of thermodynamics.

Work:

It is also a form energy that exists only in transit. The work cannot be stored. Work is defined as the product of force and distance through the force moves.

Third law of thermodynamics

The third law of thermodynamics is a statistical law of nature regarding entropy and the impossibility of reaching absolute zero of temperature. The most common enunciation of third law of thermodynamics is:

As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.

It can be concluded as 'If T=0K, then S=0' where T is the temperature of a closed system and S is the entropy of the system.

The third law was developed by Walther Nernst, during the years 1906-1912, and is thus sometimes referred to as Nernst's theorem or Nernst's postulate. The third law of thermodynamics states that the entropy of a system at zero is a well-defined constant. This is because a system at zero temperature exists in its ground state, so that its entropy is determined only by the degeneracy of the ground state; or, it states that "it is impossible by any procedure, no matter how idealised, to reduce any system to the absolute zero of temperature in a finite number of operations".

An alternative version of the third law of thermodynamics as stated by Gilbert N. Lewis and Merle Randall in 1923:

If the entropy of each element in some (perfect) crystalline state be taken as zero at the absolute zero of temperature, every substance has a finite positive entropy; but at the absolute zero of temperature the entropy may become zero, and does so become in the case of perfect crystalline substances.

This version states not only ΔS will reach zero at D = 0 K, but S itself will also reach zero.

Overview

In simple terms, the Third Law states that the entropy of a pure substance approaches zero as the absolute temperature approaches zero. This law provides an absolute reference point for the determination of entropy. The entropy determined relative to this point is the absolute entropy.

A special case of this is systems with a unique ground state, such as most crystal lattices. The entropy of a perfect crystal lattice as defined by Nernst's theorem is zero (if its ground state is singular and unique, whereby log(1) = 0). An example of a system which does not have a unique ground state is one containing half-integer spins, for which time-reversal symmetry gives two degenerate ground states. Of course, this entropy is generally considered to be negligible on a macroscopic scale. Additionally, other exotic systems are known that exhibit geometrical frustration, where the structure of the crystal lattice prevents the emergence of a unique ground state.

Real crystals with frozen defects obey this same law, so long as one considers a particular defect configuration to be fixed. The defects would not be present in thermal equilibrium, so if one considers a collection of different possible defects, the collection would have some entropy, but not actually have a temperature. Such considerations become more interesting and problematic in considering various forms of glass, since glasses have large collections of nearly degenerate states, in which they become trapped out of equilibrium.

Another application of the third law is with respect to the magnetic moments of a material. Paramagnetic materials (moments random) will order as T approaches 0 K. They may order in a ferromagnetic sense, with all moments parallel to each other, or they may order in an antiferromagnetic sense, with all moments antiparallel to each other.

Yet another application of the third law is the fact that at 0 K no solid solutions should exist. Phases in equilibrium at 0 K should either be pure elements or atomically ordered phases.

The Third Law of Thermodynamics is the lesser known of the three major thermodynamic laws. Together, these laws help form the foundations of modern science. The laws of thermodynamics are absolute physical laws - everything in the observable universe is subject to them. Like time or gravity, nothing in the universe is exempt from these laws. In its simplest form, the Third Law of Thermodynamics relates the entropy (randomness) of matter to its absolute temperature.

The Third Law of Thermodynamics refers to a state known as "absolute zero." This is the bottom point on the Kelvin temperature scale. The Kelvin scale is absolute, meaning 0° Kelvin is mathematically the lowest possible temperature in the universe. This corresponds to about -273.15° Celsius, or -459.7 Fahrenheit.

In actuality, no object or system can have a temperature of zero Kelvin, because of the Second Law of Thermodynamics. The Second Law, in part, implies that heat can never spontaneously move from a colder body to a hotter body. So, as a system approaches absolute zero, it will eventually have to draw energy from whatever systems are nearby. If it draws energy, it can never obtain absolute zero. So, this state is not physically possible, but is a mathematical limit of the universe.

In its shortest form, the Third Law of Thermodynamics says: "The entropy of a pure perfect crystal is zero (0) at zero Kelvin (0° K)." Entropy is a property of matter and energy discussed by the Second Law of Thermodynamics. The Third Law of Thermodynamics means that as the temperature of a system approaches absolute zero, its entropy approaches a constant (for pure perfect crystals, this constant is zero). A pure perfect crystal is one in which every molecule is identical, and the molecular alignment is perfectly even throughout the substance. For non-pure crystals, or those with less-than perfect alignment, there will be some energy associated with the imperfections, so the entropy cannot become zero.

The Third Law of Thermodynamics can be visualized by thinking about water. Water in gas form has molecules that can move around very freely. Water vapor has very high entropy (randomness). As the gas cools, it becomes liquid. The liquid water molecules can still move around, but not as freely. They have lost some entropy. When the water cools further, it becomes solid ice. The solid water molecules can no longer move freely, but can only vibrate within the ice crystals. The entropy is now very low. As the water is cooled more, closer and closer to absolute zero, the vibration of the molecules diminishes. If the solid water reached absolute zero, all molecular motion would stop completely. At this point, the water would have no entropy (randomness) at all.

Most of the direct use of the Third Law of Thermodynamics occurs in ultra-low temperature chemistry and physics. The applications of this law have been used to predict the response of various materials to temperature changes. These relationships have become core to many science disciplines, even though the Third Law of Thermodynamics is not used directly nearly as much as the other two.

Second Law of Thermodynamics

The second law of thermodynamics states that no heat engine can be more efficient than a reversible heat engine working between two fixed temperature limits (Carnot cycle) i.e. the maximum thermal efficiency is equal to the thermal efficiency of the Carnot cycle:

or in other words If the heat input to a heat engine is Q, then the work output of the engine, W will be restricted to an upper limit Wmax i.e.

It should be noted that real cycles are far less efficient than the Carnot cycle due to mechanical friction and other irreversibility.

The second law of thermodynamics (the entropy law or law of entropy) was formulated in the middle of the last century by Clausius and Thomson following Carnot's earlier observation that, like the fall or flow of a stream that turns a mill wheel, it is the "fall" or flow of heat from higher to lower temperatures that motivates a steam engine. The key insight was that the world is inherently active, and that whenever an energy distribution is out of equilibrium a potential or thermodynamic "force" (the gradient of a potential) exists that the world acts spontaneously to dissipate or minimize. All real-world change or dynamics is seen to follow, or be motivated, by this law. So whereas the first law expresses that which remains the same, or is time-symmetric, in all real-world processes the second law expresses that which changes and motivates the change, the fundamental time-asymmetry, in all real-world process. Clausius coined the term "entropy" to refer to the dissipated potential and the second law, in its most general form, states that the world acts spontaneously to minimize potentials (or equivalently maximize entropy), and with this, active end-directedness or time-asymmetry was, for the first time, given a universal physical basis. The balance equation of the second law, expressed as S > 0, says that in all natural processes the entropy of the world always increases, and thus whereas with the first law there is no time, and the past, present, and future are indistinguishable, the second law, with its one-way flow, introduces the basis for telling the difference.

First Law of Thermodynamics

Conservation of Energy

The principle of the conservation of energy states that energy can neither be created nor destroyed. If a system undergoes a process by heat and work transfer, then the net heat supplied, Q, plus the net work input, W, is equal to the change of intrinsic energy of the working fluid, i.e.

where U1 and U2 are intrinsic energy of the system a

t initial and final states, respectively. The special case of the equation applied to a steady-flow system is known as steady-flow energy equation. Applying this general principle to a thermodynamic cycle, when the system undergoes a complete cycle, i.e. U1 = U2, results in:

where:

Q= The algebraic sum of the heat supplied to (+) or rejected from (-) the system.
W= The algebraic sum of the work done by surround

ings on the system (+) or by the system on surroundings (-).

Applying the rule to the power plant shown in figure below,

gives:
Q = Qin - Qout
W = Win - Wout
Qin + Win - Qout - Wout = 0

where,
Qin = Heat supplied to the system through boiler,
Win = Feed-pump work,
Qout = Heat rejected from the system by condenser,
Wout = Turbine work.

In its simplest form, the First Law of Thermodynamics states that neither matter nor energy can be created or destroyed. The amount of energy in the universe is constant – energy can be changed, moved, controlled, stored, or dissipated. However, this energy cannot be created from nothing or reduced to nothing. Every natural process transforms energy and moves energy, but cannot create or eliminate it.This principle forms a foundation for many of the physical sciences.

The First Law of Thermodynamics is one of the absolute physical laws of the universe. Everything in the entire universe is affected by this law, as much as time or gravity. There are three Laws of Thermodynamics. The Second Law (Increased Entropy) and the Third Law (Zero Entropy at Zero Kelvin) are dependent on the First Law and each other. Together, these laws form part of the baseline for all modern science. No exceptions or contradictions to these laws have ever been observed.

Energy that enters a system must either be stored there or leave. A system cannot output more energy than it contains without an external source of more energy. This energy can be in work, heat, potential, or kinetic form. On a small scale, this can be explained this way: “Change in internal energy equals the difference of heat transfer into the system and the work done by the system.” On a large scale, this Law is still observable. Oceans and planets and solar systems all operate under the control of the First Law of Thermodynamics.

Some aspects of the First Law of Thermodynamics can seem confusing. A burning log in the fireplace seems to violate the principles of conservation of matter/energy. Burning the log appears to create energy and destroy matter. In reality, the energy and matter are only changing place and form, they are not being created or destroyed. The wood in the log has chemical potential energy, which is released when it is burned. This released energy appears in the form of heat and light. The matter of the log is changed into smoke particles, ash, and soot. The log’s total energy and mass before burning are the same as the mass and energy of the soot, ash, smoke, heat and light afterwards.

Rubbing your hands together generates heat on your palms. This is not actually creating energy. The work of your muscles takes the chemical energy of your body, changes it to work energy in your muscles, and then into friction (heat) energy in your skin. You’ve actually moved energy from your body through your muscles and into your hands. The First Law of Thermodynamics requires that the total energy of your body, muscles, and palms is the same both before and after you rub them together.

One example of how the First Law of Thermodynamics acts is the perpetual motion machine. No one has ever built a machine that can continue to move forever without any external energy source keeping it moving. Every machine requires some input to continue moving. This input can be wind, chemical reactions, magnets, and so forth. The reason that machines cannot move indefinitely is friction. No matter how good the lubrication or bearings are, every machine has to lose some energy to friction as it moves. This energy must come from the total energy of the system, as the First Law of Thermodynamics demands. This is why a bicycle wheel will eventually stop spinning unless you push it. This is why a car cannot coast forever on a flat surface. Friction demands some energy from the system. For a machine to run forever without any external source of energy, it would have to violate the First Law of Thermodynamics by creating energy out of nowhere.

Science has shown that the First Law of Thermodynamics applies to all matter and energy, no matter how much or what the conditions are. Looking at bigger and bigger systems of matter and energy eventually leads to a question: where did all of the matter and energy in the universe come from? The Second Law of Thermodynamics shows us that all of the energy in the universe is moving towards a less “useable” form. However, the First Law of Thermodynamics shows us that nothing in the physical universe can create or destroy that matter or energy. If nothing natural can create matter or energy, then something supernatural must have created them.

Zeroth Law of Thermodynamics

This law states that if object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object C is also in thermal equilibrium with object A. This law allows us to build thermometers. For example the length of a mercury column (object B) may be used as a measure to compare the temperatures of the two other objects.

Other definition

The zeroth law of thermodynamics is an observation. When two objects are separately in thermodynamic equilibrium with a third object, they are in equilibrium with each other.

This simple observation allows us to create a thermometer. We can calibrate the change in a thermal property, such as the length of a column of mercury, by putting the thermometer in thermal equilibrium with a known physical system at several reference points. Celsius thermometers have the reference points fixed at the freezing and boiling point of pure water. If we then bring the thermometer into thermal equilibrium with any other system, such as the bottom of your tongue, we can determine the temperature of the other system by noting the change in the thermal property. Objects in thermodynamic equilibrium have the same temperature.

It is observed that some property of an object, like the pressure in a volume of gas, the length of a metal rod, or the electrical conductivity of a wire, can change when the object is heated or cooled. If two of these objects are brought into physical contact there is initially a change in the property of both objects. But, eventually, the change in property stops and the objects are said to be in thermal, or thermodynamic, equilibrium. Thermodynamic equilibrium leads to the large scale definition of temperature. When two objects are in thermal equilibrium they are said to have the same temperature. During the process of reaching thermal equilibrium, heat, which is a form of energy, is transferred between the objects.

Law of Thermodynamics

The zeroth law of thermodynamics involves some simple definitions of thermodynamic equilibrium. Thermodynamic equilibrium leads to the large scale definition of temperature, as opposed to the small scale definition related to the kinetic energy of the molecules. The first law of thermodynamics relates the various forms of kinetic and potential energy in a system to the work which a system can perform and to the transfer of heat. This law is sometimes taken as the definition of internal energy, and introduces an additional state variable, enthalpy. The first law of thermodynamics allows for many possible states of a system to exist. But experience indicates that only certain states occur. This leads to the second law of thermodynamics and the definition of another state variable called entropy. The second law stipulates that the total entropy of a system plus its environment can not decrease; it can remain constant for a reversible process but must always increase for an irreversible process.

Thermodynamics

Thermodynamics is a branch of physics which deals with the energy and work of a system. It was born in the 19th century as scientists were first discovering how to build and operate steam engines. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. Small scale gas interactions are described by the kinetic theory of gases.

Thermodynamics is a branch of physics and of chemistry that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. Roughly, heat means "energy in transit" and dynamics relates to "movement"; thus, in essence thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the efficiency of early steam engines.

Typical thermodynamic system - heat moves from hot (boiler) to cold (condenser), and work is extracted.

The starting point for most thermodynamic considerations are the laws of thermodynamics, which postulate that energy can be exchanged between physical systems as heat or work. They also postulate the existence of a quantity named entropy, which can be defined for any system. In thermodynamics, interactions between large ensembles of objects are studied and categorized. Central to this are the concepts of system and surroundings. A system is composed of particles, whose average motions define its properties, which in turn are related to one another through equations of state. Properties can be combined to express internal energy and thermodynamic potentials, which are useful for determining conditions for equilibrium and spontaneous processes.

With these tools, thermodynamics describes how systems respond to changes in their surroundings. This can be applied to a wide variety of topics in science and engineering, such as engines, phase transitions, chemical reactions, transport phenomena, and even black holes. The results of thermodynamics are essential for other fields of physics and for chemistry, chemical engineering, aerospace engineering, mechanical engineering, cell biology, biomedical engineering, and materials science.

Thermodynamic systems

An important concept in thermodynamics is the “system”. Everything in the universe except the system is known as surroundings. A system is the region of the universe under study. A system is separated from the remainder of the universe by a boundary which may be imaginary or not, but which by convention delimits a finite volume. The possible exchanges of work, heat, or matter between the system and the surroundings take place across this boundary. Boundaries are of four types: fixed, moveable, real, and imaginary.

Basically, the “boundary” is simply an imaginary dotted line drawn around a volume of something when there is going to be a change in the internal energy of that something. Anything that passes across the boundary that effects a change in the internal energy of the somethingsomething can be the volumetric region surrounding a single atom resonating energy, such as Max Planck defined in 1900; it can be a body of steam or air in a steam engine, such as Sadi Carnot defined in 1824; it can be the body of a tropical cyclone, such as Kerry Emanuel theorized in 1986 in the field of atmospheric thermodynamics; it could also be just one nuclide (i.e. a system of quarks) as some are theorizing presently in quantum thermodynamics. needs to be accounted for in the energy balance equation. That

For an engine, a fixed boundary means the piston is locked at its position; as such, a constant volume process occurs. In that same engine, a moveable boundary allows the piston to move in and out. For closed systems, boundaries are real while for open system boundaries are often imaginary. There are five dominant classes of systems:

1. Isolated Systems – matter and energy may not cross the boundary
2. Adiabatic Systems – heat must not cross the boundary
3. Diathermic Systems - heat may cross boundary
4. Closed Systems – matter may not cross the boundary
5. Open Systems – heat, work, and matter may cross the boundary (often called a control volume in this case)

As time passes in an isolated system, internal differences in the system tend to even out and pressures and temperatures tend to equalize, as do density differences. A system in which all equalizing processes have gone practically to completion is considered to be in a state of thermodynamic equilibrium.

In thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems which are not in equilibrium. Often, when analysing a thermodynamic process, it can be assumed that each intermediate state in the process is at equilibrium. This will also considerably simplify the situation. Thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state are said to be reversible processes.