Talk:Boltzmann constant/Archive 2

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the boltzmann constant in hartree doesn't seem to be right!

Values of k Units Comments 1.380 6504(24) × 10−23 J/K SI units, 2006 CODATA value 8.617 343(15) × 10−5 eV/K 1 electronvolt = 1.602 176 53(14) × 10−19 J 1/kB = 11 604.51(2) K/eV

2.303 6644(36) × 1010 Hz/K 6.336 281(73) × 10−6 EH/K 1 hartree = 27.211 383 86(68) eV = 4.359 74394(22) × 10−18 J

that number of 6.336281 seems to be half of it, 3.16682!

--Yingchiehsun (talk) 02:59, 12 May 2009 (UTC)

Well spotted! You can check the conversion at the NIST site. Strangely, the conversion factors from hartrees to electronvolts and joules were correct, but whoever had added the value of the Boltzmann constant had forgotten that E_H = 2R_∞. Physchim62 (talk) 09:26, 12 May 2009 (UTC)

conversion factor

Why does this table list 4.1868 as the conversion factor for joules and calories? Surely the appropriate conversion is 4.184 since we're talking thermodynamics —Preceding unsigned comment added by 206.248.179.192 (talk • contribs) 04:30, 11 August 2010

More to the point, the article should be specifying which of the many flavours of calorie is intended. SpinningSpark 17:24, 11 August 2010 (UTC)

Thermal voltage section has Boltzmann constant in the wrong units

The Boltzmann constant should be 1.380 6504(24) × 10−23 J/K instead of 8.617 343(15) × 10−5 eV/K if you are using Coulomb for the charge of an electron. —Preceding unsigned comment added by 167.225.107.17 (talk) 15:46, 20 September 2010 (UTC)

What is your problem, both systems of units are given. SpinningSpark 18:23, 20 September 2010 (UTC)

If we choose to measure temperature in units of energy....

This statement appears at the end of the article: 'If we choose to measure temperature in units of energy then Boltzmann's constant would not be needed at all.[7]'. It is nonsense; if temperature were measured in units of energy then a statement such as 'the temperature is 10 Joules' would be meaningful, it isn't. --Damorbel (talk) 07:27, 26 January 2011 (UTC)

It is meaningful to say "the temperature is such that the amount of energy needed to raise the entropy by one nat is 10 Joules". The point being made is that that establishes a particularly natural scale for temperature, similar to choosing a scale for force such that the constant of proportionality in $\scriptstyle {P\;\propto \;ma}$ comes out to be unity. But perhaps the article should say "in units of energy per nat". Jheald (talk) 09:16, 26 January 2011 (UTC)

Naturally entropy is the conjugate of temperature, so in systems of units with k=1, the relation to the nat is completely implicit, so that this language is really not necessary and complicates the presentation needlessly. Kbrose (talk) 21:50, 26 January 2011 (UTC)

Temperature and entropy, although connected in some respects, must be distinguished. Check this - Intensive and extensive properties. Temperature is an intensive property, a thermodynamic system almost certainly has different temperatures at different locations, the same system will have only one entropy because entropy is an extensive property. Unless the temperature is uniform throughout the entropy will not be a maximum. It would be possible to divide the system into subsystems, each with its own entropy contributing to the system entropy but that remains the same as describing temperature as an intensive property. Another fact - a system must be in equilibrium i.e at maximum entropy, to have a definite temperature. --Damorbel (talk) 14:02, 26 January 2011 (UTC)

What is it you don't understand about E = 1/2 kT ? Isn't that clear enough that temperature is just another expression of energy, of a certain kind of energy? k is simply a conversion factor of units, that does not change any kind of underlying physics. The most elegant, pure description of physics results when k=1 as is often practiced. You have been told this over and over again in various articles, yet you keep belaboring this topic for months without showing any kind progress of understanding. Please stop engaging in these endless, non-productive cyclical arguments, inquiries, and debates. You are wasting people's time. Kbrose (talk) 21:50, 26 January 2011 (UTC)

If as you say "Isn't that clear enough that temperature is just another expression of energy, of a certain kind of energy?" then it should be possible to express temperature in terms of energy Joules or ergs. An analogous comparison is Volt (potential), Coulomb (charge) and Farad (capacitance). Let Volt correspond to Kelvin, Coulomb to Joule and Farad to either k_B(Boltzmann constant), R (gas constant) or C (heat capacity); The Volt is not a measure of charge, it is the potential measured accross the terminals of a one Farad capacitor containing a charge of one one Joule; with a capacitance of 1/2Farad 1 Joule would give 2 volts; thus the potential E relates to charge Q on capacitor C like this:- E = Q/C.

Now k_B (Boltzmann constant), R (gas constant) and C (heat capacity) are related by numbers that only differ in the amount of material present; k_B = R/N_A N_A is Avogadro's number - the number of molecules in a mole of an ideal gas and C (heat capacity) is the heat capacity of a mole of any substance. So, as it says in the first line of the article, "the Boltzmann constant (k or k_B) is the physical constant relating energy at the individual particle level with temperature observed at the collective or bulk level".--Damorbel (talk) 08:41, 27 January 2011 (UTC)

The gas law says that the number pV/T=nR=Nk is a measure of the amount of gas. n is the number of mols, and N is the number of molecules. So the gas constant R has the unit of joule per kelvin per mole, and the Boltzmann constant k has the unit of joule per kelvin per molecule. So k is the amount of gas pV/T for one molecule. A lot of confusion arises by the unnecessary use of the unit mole. I wonder how it was ever standardized. The joule per kelvin is an SI unit for amount of matter. Bo Jacoby (talk) 10:22, 27 January 2011 (UTC).

Bo Jacoby, I have indented your paragraph for clarity. I have edited my previous contribution to change Avogadro's number from N to N_A. I agree about the mole, I think it is a (mistaken) attempt to 'simplify' the concept of molecular energy. Molecules are a big hazard when studying thermodynamics because there is only a loose connection between molecular structure and heat capacity.--Damorbel (talk) 11:39, 27 January 2011 (UTC)

Thank you. I am no sure I understand you comment on molecular energy and heat capacity, but I notice the simplification of thermodynamical equations by omitting R and using the joule per kelvin unit for amount of matter. For example the specific heat of a substance becomes dimensionless. (J/K per J/K). Bo Jacoby (talk) 15:57, 27 January 2011 (UTC).

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