18-01-2013, 03:21 PM
LAWS OF THERMODYNAMICS
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THERMODYNAMICS
In physics, thermodynamics is the study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, volume and pressure. 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 isolated system that is in thermodynamic equilibrium. 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.
ZEROTH LAW
If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
When two systems are put in contact with each other, there will be a net exchange of energy between them unless or until they are in thermal equilibrium. That is the state of having equal temperature. Although this concept of thermodynamics is fundamental, the need to state it explicitly was not widely perceived until the first third of the 20th century, long after the first three principles were already widely in use. Hence it was numbered zero -- before the subsequent three.
FIRST LAW
Energy can neither be created nor destroyed. It can only change forms.
In any process in an isolated system, the total energy remains the same.
For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.
FUNDAMENTAL THERMODYNAMIC RELATION
The first law can be expressed as the fundamental thermodynamic relation:
Heat supplied to a system = increase in internal energy of the system + work done by the system
Increase in internal energy of a system = heat supplied to the system - work done by the system
Here, E is internal energy, T is temperature, S is entropy, p is pressure, and V is volume. This is a statement of conservation of energy: The net change in internal energy (dE) equals the heat energy that flows in (TdS), minus the energy that flows out via the system performing work (pdV).
SECOND LAW
The entropy of an isolated system consisting of two regions of space, isolated from one another, each in thermodynamic equilibrium in itself, but not in equilibrium with each other, will, when the isolation that separates the two regions is broken, so that the two regions become able to exchange matter or energy, tend to increase over time, approaching a maximum value when the jointly communicating system reaches thermodynamic equilibrium.
THIRD LAW
As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.
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.
TENTATIVE FOURTH LAWS…
Over the years, various thermodynamic researchers have come forward to ascribe to or to postulate potential fourth laws of thermodynamics (either suggesting that a widely-accepted principle should be called the fourth law, or proposing entirely new laws); in some cases, even fifth or sixth laws of thermodynamics are proposed. Most fourth law statements, however, are speculative and controversial.
The most commonly proposed Fourth Law is the Onsager reciprocal relations, which give a quantitative relation between the parameters of a system in which heat and matter are simultaneously flowing.
[attachment=47533]
THERMODYNAMICS
In physics, thermodynamics is the study of energy conversion between heat and mechanical work, and subsequently the macroscopic variables such as temperature, volume and pressure. 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 isolated system that is in thermodynamic equilibrium. 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.
ZEROTH LAW
If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
When two systems are put in contact with each other, there will be a net exchange of energy between them unless or until they are in thermal equilibrium. That is the state of having equal temperature. Although this concept of thermodynamics is fundamental, the need to state it explicitly was not widely perceived until the first third of the 20th century, long after the first three principles were already widely in use. Hence it was numbered zero -- before the subsequent three.
FIRST LAW
Energy can neither be created nor destroyed. It can only change forms.
In any process in an isolated system, the total energy remains the same.
For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.
FUNDAMENTAL THERMODYNAMIC RELATION
The first law can be expressed as the fundamental thermodynamic relation:
Heat supplied to a system = increase in internal energy of the system + work done by the system
Increase in internal energy of a system = heat supplied to the system - work done by the system
Here, E is internal energy, T is temperature, S is entropy, p is pressure, and V is volume. This is a statement of conservation of energy: The net change in internal energy (dE) equals the heat energy that flows in (TdS), minus the energy that flows out via the system performing work (pdV).
SECOND LAW
The entropy of an isolated system consisting of two regions of space, isolated from one another, each in thermodynamic equilibrium in itself, but not in equilibrium with each other, will, when the isolation that separates the two regions is broken, so that the two regions become able to exchange matter or energy, tend to increase over time, approaching a maximum value when the jointly communicating system reaches thermodynamic equilibrium.
THIRD LAW
As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.
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.
TENTATIVE FOURTH LAWS…
Over the years, various thermodynamic researchers have come forward to ascribe to or to postulate potential fourth laws of thermodynamics (either suggesting that a widely-accepted principle should be called the fourth law, or proposing entirely new laws); in some cases, even fifth or sixth laws of thermodynamics are proposed. Most fourth law statements, however, are speculative and controversial.
The most commonly proposed Fourth Law is the Onsager reciprocal relations, which give a quantitative relation between the parameters of a system in which heat and matter are simultaneously flowing.