Talk:Engineering Thermodynamics/Third Law

There are TWO "thirs law"s of thermodynamics
before 2006 all refrences stated that:
 * "The second law suggests the existence of an absolute temperature scale that includes an absolute zero of temperature. The third law of thermodynamics states that absolute zero cannot be attained by any procedure in a finite number of steps. Absolute zero can be approached arbitrarily closely, but it can never be reached." (Source: Microsoft Encarta 2006, The multimedia Encyclopedia)

but then suddenly it changed to:
 * "In a perfect crystal at tempreture of absolute zero, Enthropy is zero" (Source:Thermodynamics by Yunus A. Cenjel)

first one is sayd to be wrong, because in absolute zero the movement of molecules reaches to zero

The second one is not a rule. it is a definition. a rule is a positive/negative statement that untill now experiments have always happened according to it/have not happend otherwise. the second one can't be proved. but it's validation can be limited with a single experiment happening otherwise


 * I'm not sure how, but I'm sure there's some way that those two statements of the third law are equivalent (possibly because an implication of the second law is that it's impossible to reach a state where the entropy is zero, though this is merely guesswork). The second statement is more like a definition, you're correct; since we never know the absolute amount of entropy (or enthalpy or internal energy for that matter) something has, but if we define a standard state we can measure the quantities relative to the standard (and since they're state variables, it doesn't matter how we get from one state to the other). 76.23.193.130 (talk) 02:51, 24 September 2008 (UTC)