NYGH 304 Physics SIA: Nuclear Energy-

Monday, March 31, 2008

-- Emily Chua Him Woon (8) 304

The laws of thermodynamics, in principle, describe the specifics for the transport of heat and work in thermodynamic processes. There are altogether actually 4 laws of thermodynamics and they are the Zeroth Law, First Law, Second Law and the Third Law respectively.

The Zeroth Law is the law that states that “If two thermodynamics systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. When 2 systems are put in contact with each other, there will be a net exchange of energy between them unless they are in thermal equilibrium which means to say that they contain the same amount of thermal energy for a given volume. A good example is when a higher temperature object which is in contact with a lower temperature object will transfer its heat to the lower temperature object. The objects will approach the same temperature, and in the absence of loss to other objects, they will then maintain a constant temperature. Hence to summarise, thermal equilibrium is the subject of the Zeroth Law of thermodynamics. This Law was perceived in the 20th century, long after the first three Laws were already in use, and hence, it was named the Zeroth Law.

The First Law of thermodynamics which is also known as the Law of Conservation of Energy, is “The sum of heat applied to the system and the net work done by the system is equals to zero.” The First Law of thermodynamics also states that energy cannot be destroyed or created; rather, the amount of energy lost in steady process cannot be greater than the amount of energy gained. This refers to a two ways that a closed system can transfer its energy to and from its surroundings- by the process of heating or cooling and the process of mechanical work. The rate of gain or loss in the stored energy of the system is determined by the rate of these two processes. The First Law of thermodynamics proves that energy is a stored quantity which is independent of any particular process path and that energy cannot be created or destroyed. The First Law can be also defined as “the change in internal energy of a system is equals to the heat added to the system minus the work done by the system.”

The second law of thermodynamics is an expression of the universal law of increasing entropy, stating that the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium. Entropy is a measure of the unavailability of a system’s energy to do work. Entropy is also a gauge of randomness or chaos within a closed system. For an example, a broken cup has less order and more chaos than an intact one.

The Third Law of thermodynamics means that as a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value. For example; Water in gas form has molecules that can move around very freely. Therefore, it has very high entropy. 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.

References :

AllAboutScience.org（2002－2008）Second Law of Thermodynamics［on-line］http://www.allaboutscience.org/second-law-of-thermodynamics.htm (10-03-08)

Thermodynamics
www.hyperphysics.phy- astr.gsu.edu/hbase/thermo/seclaw.html(10-03-08)

Thermodynamics
www.infoplease.com/ce6/sci/A0861526.html (10-03-08)

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