Laws of thermodynamics

The laws of thermodynamics, in The laws of thermodynamics, in principle, describe the specifics for the principle, describe the specifics for the transport of heat and work in transport of heat and work in thermodynamic processes. Since their thermodynamic processes. Since their inception, however, these laws have inception, however, these laws have become some of the most important in become some of the most important in all of physics and other branches of all of physics and other branches of science connected to thermodynamics.science connected to thermodynamics.

FAMILIARIZATIONFAMILIARIZATION

The The zeroth lawzeroth law of thermodynamics, which underlies the of thermodynamics, which underlies the definition of temperature.definition of temperature.

The The first lawfirst law of thermodynamics, which mandates of thermodynamics, which mandates conservation of energy, and states in particular that heat is a conservation of energy, and states in particular that heat is a form of energy.form of energy.

The The second lawsecond law of thermodynamics, which states that the of thermodynamics, which states that the entropy of the universe always increases, or (equivalently) entropy of the universe always increases, or (equivalently) that perpetual motion machines are impossible.that perpetual motion machines are impossible.

The The third lawthird law of thermodynamics, which concerns the of thermodynamics, which concerns the entropy of an object at absolute zero temperature, and entropy of an object at absolute zero temperature, and implies that it is impossible to cool a system all the way to implies that it is impossible to cool a system all the way to exactly absolute zero.exactly absolute zero.


The The zeroth lawzeroth law of thermodynamics, which underlies the of thermodynamics, which underlies the definition of temperature.definition of temperature.

The The first lawfirst law of thermodynamics, which mandates of thermodynamics, which mandates conservation of energy, and states in particular that heat is a conservation of energy, and states in particular that heat is a form of energy.form of energy.

The The second lawsecond law of thermodynamics, which states that the of thermodynamics, which states that the entropy of the universe always increases, or (equivalently) entropy of the universe always increases, or (equivalently) that perpetual motion machines are impossible.that perpetual motion machines are impossible.

The The third lawthird law of thermodynamics, which concerns the of thermodynamics, which concerns the entropy of an object at absolute zero temperature, and entropy of an object at absolute zero temperature, and implies that it is impossible to cool a system all the way to implies that it is impossible to cool a system all the way to exactly absolute zero.exactly absolute zero.


Internal Energy:Internal Energy: It is defined as the energy associated It is defined as the energy associated with the random, disordered motion of molecules. It is with the random, disordered motion of molecules. It is separated in scale from the macroscopic ordered energy separated in scale from the macroscopic ordered energy associated with moving objects; it refers to the invisible associated with moving objects; it refers to the invisible microscopic energy on the atomic and molecular scale. For microscopic energy on the atomic and molecular scale. For example, a room temperature glass of water sitting on a example, a room temperature glass of water sitting on a table has no apparent energy, either potential or kinetic . table has no apparent energy, either potential or kinetic . But on the microscopic scale it is a seething mass of high But on the microscopic scale it is a seething mass of high speed molecules. If the water were tossed across the speed molecules. If the water were tossed across the room, this microscopic energy would not necessarily be room, this microscopic energy would not necessarily be changed when we superimpose an ordered large scale changed when we superimpose an ordered large scale motion on the water as a whole.motion on the water as a whole.


Heat:Heat: It may be defined as energy in transit It may be defined as energy in transit from a high temperature object to a lower from a high temperature object to a lower temperature object. An object does not temperature object. An object does not possess "heat"; the appropriate term for the possess "heat"; the appropriate term for the microscopic energy in an object is internal microscopic energy in an object is internal energy. The internal energy may be increased energy. The internal energy may be increased by transferring energy to the object from a by transferring energy to the object from a higher temperature (hotter) object - this is higher temperature (hotter) object - this is called heating.called heating.


Work:Work: When work is done by a When work is done by a thermodynamic system, it is usually a gas that is thermodynamic system, it is usually a gas that is doing the work. The work done by a gas at doing the work. The work done by a gas at constant pressure is W = p dV, where W is work, constant pressure is W = p dV, where W is work, p is pressure and dV is change in volume.p is pressure and dV is change in volume.For non-constant pressure, the work can be For non-constant pressure, the work can be visualized as the area under the pressure-volume visualized as the area under the pressure-volume curve which represents the process taking place.curve which represents the process taking place.

The Zeroth LawThe Zeroth LawThis law expresses that having in existence This law expresses that having in existence three systems, A, B, and C, if A is in three systems, A, B, and C, if A is in equilibrium with C and B is in equilibrium with equilibrium with C and B is in equilibrium with C, then A and B will also be in equilibrium. All C, then A and B will also be in equilibrium. All three systems will be in equilibrium in three systems will be in equilibrium in temperature. If any of these systems are in temperature. If any of these systems are in contact with other systems, there will be contact with other systems, there will be compensation in the temperature level of all compensation in the temperature level of all the systems involved. That is, they will all the systems involved. That is, they will all have the same temperature.have the same temperature. Mathematically, we know that,Mathematically, we know that,

if A= B & A=C if A= B & A=C then A=B=Cthen A=B=C

Thermodynamically, as per the Zeroth Law, Thermodynamically, as per the Zeroth Law, if Tif TAA= T= TBB & T & TAA=T=TCC then Tthen TAA= T= TBB =T =TCC


Work:Work: When work is done by a When work is done by a thermodynamic system, it is usually a gas that is thermodynamic system, it is usually a gas that is doing the work. The work done by a gas at doing the work. The work done by a gas at constant pressure is W = p dV, where W is work, constant pressure is W = p dV, where W is work, p is pressure and dV is change in volume.p is pressure and dV is change in volume.For non-constant pressure, the work can be For non-constant pressure, the work can be visualized as the area under the pressure-volume visualized as the area under the pressure-volume curve which represents the process taking place.curve which represents the process taking place.

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Laws of thermodynamics