What is the 3 law of thermodynamics?

Answer 1

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

Answer 2

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.

Answer 3

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.

Answer 4

The entropy of all homogeneous crystalline solid substances is zero at absolute zero temperature

Answer 5

In essence it is that when approaching Absolute Zero the entropy of most substances also approaches zero