There is no accepted or established "fourth law of thermodynamics". There are, however, numerous authors who have postulated versions of fourth laws to explain certain aberrant phenomena. The following link gives over fifteen different versions of postulated "fourth" laws of thermodynamics: http://www.humanthermodynamics.com/4th-Law-Variations.html
The "3rd law" is sometimes expressed as:
The entropy of a perfect crystal at absolute zero is exactly equal to zero.
Perhaps a more useful way to state the 3rd law is:
It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its zero point value in a finite number of operations.The idea is that the perfect crystal at a temperature of absolute zero is perfectly ordered. The atoms of the crystal are locked in position and not moving.They are at the absolute lowest energy state that they can be in.ANY change would require adding energy thus, by the definition of entropy, would increase the entropy of the system. One implication of this is that it is impossible to reduce any system to this minimum value since, according the the second law, you must have a system at a lower temperature to absorb energy from the higher temperature system. Even if youcould start with asystem already at absolute zero you could not use it to reduce another system to absolute zero; you would wind up with two systems above absolute zero once the exchange of energy occured.
The third law defines the conditions of "absolute zero". The entropy of a perfect crystal at absolute zero is exactly equal to zero. In other words, if you have an object with absolutely no molecular motion and perfectly ordered - thus no disorder, you have no entropy and the thermal state of the object corresponds to what we define as absolute zero. It's the condition where the object is at it's absolute minimum energy state - where any change to it would increase its energy.
The law can also be stated as:
The entropy change associated with any condensed system undergoing a reversible isothermal process approaches zero as the temperature at which it is performed approaches 0.
As a consequence:
It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its absolute-zero value in a finite number of operations.
"Unavailable for doing work" is related to the Second Law of Thermodynamics.
Thermodynamics is both a law and a theory. It has a set of well-established laws, such as the first and second laws of thermodynamics, which describe the behavior of energy in systems. Additionally, the principles and concepts underlying thermodynamics are formulated into a theory to explain and predict the behavior of physical systems.
Second Law of Thermodynamics
The Second Law of Thermodynamics.
the internal energy (thermal energy)
Not exactly. The first law of thermodynamics, i.e. the law of conservation of energy, also accounts for heat as one of the many forms that energy can take. There is no one law called "the law of thermodynamics", but there are several "Laws of Thermodynamics" (note the plural form "LAWS").
Thermodynamic cycle is based on 2nd law of thermodynamics.
Magic
The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. This is a restatement of the law of conservation of energy.
The first law of thermodynamics is also known as the Law of Energy Conservation.
"Unavailable for doing work" is related to the Second Law of Thermodynamics.
Entropy is closely related to the 2nd law of thermodynamics, not the 1st law. The 1st law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted. Entropy, on the other hand, is a measure of the disorder or randomness of a system, which increases over time according to the 2nd law of thermodynamics.
The first law of thermodynamics, also known as the Law of Conservation of Energy, states that energy can neither be created nor destroyed, only transferred or converted from one form to another.
The fact that usable energy is always lost in an energy transfer is due to the second law of thermodynamics. This law states that entropy, or disorder, tends to increase over time in a closed system, leading to the loss of usable energy in the form of heat.
Thermodynamics is both a law and a theory. It has a set of well-established laws, such as the first and second laws of thermodynamics, which describe the behavior of energy in systems. Additionally, the principles and concepts underlying thermodynamics are formulated into a theory to explain and predict the behavior of physical systems.
The first law of thermodynamics states that energy cannot be created or destroyed in an isolated system; it can only change forms. This law is also known as the Law of Conservation of Energy.
There is no commonly accepted law by that name, as far as I know. Two important laws about energy are the First Law of Thermodynamics and the Second Law of Thermodynamics.