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Physics C‑class High‑importance

This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics C This article has been rated as C-class on Wikipedia's content assessment scale. High This article has been rated as High-importance on the project's importance scale.

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Moving the merged article back from Specific heat capacity, as this is the more fundamental quantity. The bulk of the article I've now copied across, and adapted as required to make heat capacity in general the primary focus, rather than specific heat capacity.

Still to do:

• Background. More qualitative discussion would be good, before jumping into all the scary algebra of the thermodynamics section. fr.wiki has a nice couple of lines on the replacement of the caloric view with the energetic view, which would fit well with a references to history and early works. Done. There is also quite a lot of material in the lead and first section of the specific heat article, which maybe should be adapted and carried over; though it's written very much around specific heat, so I have left it out initially. Now partly done, under "Metrology" and "Alternate units". A little more to do.
• Earlier main discussion of specific heat capacity, molar heat capacity. It doesn't really fit where it is at the moment, the article would benefit by treating the intensive variants earlier; the "definitions and formal properties" section would also benefit from the streamlining. de.wiki's article is very terse and effective on this, might be worth adapting. Done.
• Alternative units. Again, the current specific heat article makes quite a lot of this, and they probably should get mentioned. Done. Also the 25°C standard temperature. Probably best just after the discussion of specific heat capacity and molar heat capacity. Done.
• Lead. Should summarise the whole article. Holding text for the moment; definitely needs revision, but probably easier after the 3 sections above are more in place.
• Theory of heat capacity. Needs some spring cleaning and streamlining, to make sure the ideas actually flow -- it starts with rather a jump into the middle at the moment.
• Negative heat capacity. de-wiki has a paragraph on this. Done.
• Ratio of specific heats. We ought to have a mention of γ.
• Dimensionless heat capacity. Relate to dimensionless entropy. Review existing "mutual information" reference -- factors look wrong to me. Done

No doubt there's more, but that's enough to start with. Jheald (talk) 11:24, 29 April 2010 (UTC). Updated. Jheald (talk) 13:56, 29 April 2010 (UTC)[reply]

I've added back in a paragraph from the specific heat intro which summarizes the microscopic theory section somewhat. LEDE is too short, as it is, and this won't hurt.

Regarding gamma, it's interested that even the main article Relations between heat capacities doesn't give the ratio of Cp/Cv a name. Or if so, I missed it. Here's the natural place to add it, in both articles. SBHarris 22:09, 29 April 2010 (UTC)[reply]

• COMPARE RESULTS FROM EXPERIMENT WITH THEORETICAL VALUE —Preceding unsigned comment added by 210.48.147.2 (talk) 03:27, 28 September 2010 (UTC)[reply]

• Discussion of other intensive heat capacity quantities. The word "specific" means "divided by something". Thus we have mole-specific heat capacity (C/mole), mass-specific heat capacity (C/mass), and (for solids) volume-specific heat capacity (C/volume). The lead of this article blithley assumes that specific heat always means mass-specific heat, when that is not the case at all. I've really had a problem with the other editors on this article. I quote from my engineering heat transfer books, and they simply removed the references and go back to their pet beliefs about what they learned about what things are called. Maybe in their chem and physics classes or texts-- I don't know. But the concept of "specific heat" is used in many fields. And it would be nice if some of people who toss about the word "specific" in the physical sciences, had some idea of THAT term comes from. SBHarris 02:02, 22 November 2010 (UTC)[reply]

This characterization is simply wrong, pov, and not supported by any references. The lone prefix specific is always understood in physics, chemistry, and yes, engineering, as a mass-specific parameter, when no other explanations are explicitly present. IUPAC and the BIPM/SI brochure are also rater clear and unambiguous about this usage, which is now referenced in this article. Mole specific heat capacity is never used, and mass-specific extremely rarely, when it is absolutely needed to distinguish from the volumetric property. Kbrose (talk) 05:48, 22 November 2010 (UTC)[reply]

You could find the references yourself if you bothered. Enter "mole specific heat capacity" into Google scholar and you'll find 16 references to papers and science texts that use the term (is 16 = "never" in your personal number system?) Do the same with "molar specific heat capcity" (use the quotes) and you will get 146 references. Even farther from never, if my memory of the number line serves.

One of your references says that "specific" USUALLY refers to "mass specific," not that it never does or is "always understood" to refer to mass-- you even quoted the usually in your cite; did you understand it? IUPAC now recommends that the lone term "specific heat capacity" always refer to mass-specific heat capacity and that's fine with me. I left that in. But what you say about "The lone prefix specific is always understood in physics, chemistry, and yes, engineering, as a mass-specific parameter, when no other explanations are explicitly present" is contradicted by about 20 perfectly well defined and commonly used engineering and science terms, which have no better explanations than the ones given for intensive specific heat quantities discussed in this article:

• Specific fuel consumption, disambiguation. Fuel consumption per unit thrust, or per unit power. Type needs definition in context.
• Specific acoustic impedance, ratio of sound pressure p to particle velocity v at a single frequency
• Specific conductance, conductance per meter. Same as electrical conductivity
• Specific gas constant, per molar mass
• Specific gravity, relative density with respect to water (density per water density)
• Specific heat of vaporization, enthalpy of vaporization, vaporizing heat per mole
• Specific humidity, ratio of water vapor to air (including water vapor and dry air) in a particular mass
• Specific impulse, impulse (momentum change) per unit of propellant (either per unit of propellant mass, or per unit of propellant by Earth-weight)
• Specific mass, actually meaning volume-specific mass, or mass per unit volume. Same as density
• Specific melting heat, enthalpy of fusion; melting heat per mole
• Specific modulus, elastic modulus per mass density (not per mass unit)
• Specific resistance, resistance per meter. Same as electrical resistivity
• Specific speed, unitless figure of merit used to classify pump impellers (pump-specific) and turbines (turbine-specific). Ratio of performance against reference pump that needs one unit of speed to pump one unit volume per one unit hydraulic head pressure. For a turbine, it is performance measured against a reference turbine that develops one unit of power per one unit speed per one unit of hydraulic head.
• Specific strength, material strength (pressure required at failure) per unit material density.
• Specific surface area, per unit of mass, but also per unit volume, or cross-sectional area
• Specific surface energy, free energy per unit surface-area
• Specific thrust, thrust per unit air intake rate
• Specific weight, weight per unit volume

Actually there are more than 20 there, but does the number 20 = "never" in your system of term-counting? That's an interesting POV, if true. You know, you could actually learn something about the history and actual terminology in the present day in the sciences, including use of the word "specific," if you were willing to be educated. Any of the terms used above can be "Google Scholar"ed for references to texts and peer-reviewed articles. Do you want to try one, and see? So do it and learn something. Don't just tell me I don't know what I'm talking about. The person who is clueless about terminology here, would be you. SBHarris 07:11, 22 November 2010 (UTC)[reply]

• "Nevertheless, for sufficiently high temperatures, these degrees of freedom cannot be ignored"
• "Thus, it is the heat capacity per-mole-of-atoms, not per-mole-of-molecules, which is the intensive quantity, and which comes closest to being a constant for all substances at high temperatures"
• "Furthermore (although at generally higher temperatures yet) internal vibrational degrees of freedom also may become active."
• "At higher temperatures, however, nitrogen gas gains two more degrees of internal freedom, as the molecule is excited into higher vibrational modes which store thermal energy"

There seems to be a lot of use of the qualitative phrase "high temperature". But high temperatures in cryogenics are a coupe milliKelvin, and high temperatures in plasma physics are tens of thousands of Kelvin. The example of HCl is given (4165 K) which helps to provide a sense of scale to what is meant by the phrase "high temperature", but in general I would encourage use of more specific terms throughout the article.--JB Gnome (talk) 22:23, 21 November 2010 (UTC)[reply]

It's been my experience that heat capacity is capital C, and specific heat capacity is lower case c. The article mixes them. If this is a general convention, could we update the article? One particular example is the table of specific heat capacities; the first column should certainly be lower case c to agree with the article. I've gone ahead and changed that, but I'd appreciate if someone more knowledgeable could confirm my hunch. Khakiandmauve (talk) 19:26, 24 November 2010 (UTC)[reply]

The heat capacity for water(ice) was inappropriately low. Clearly the molar mass of water does not change between phases. --Hansonrstolaf (talk) 23:42, 6 January 2011 (UTC)[reply]

Also: the given value for wood (in the building materials table) seems about 10x too large. - please fix. PB 20130605 — Preceding unsigned comment added by 81.151.170.144 (talk) 09:15, 5 June 2013 (UTC)[reply]

In the section Thermodynamic relations and definition of heat capacity, User:65.183.8.194 changed the sign of the infinitesimal work term in the equation dU = dQ (was plus, now minus) dW. We never really define anywhere what convention we use, but I think it's typical to define work done on the system as positive, and work done by the system as negative; therefore, the proper form would be dU = dQ + dW. Thoughts? Khakiandmauve (talk) 21:44, 18 April 2011 (UTC)[reply]

Take a look at the equation following the text: 'this equation reduces simply to Mayer's relation'. it is not clear to me why there is a lowercase subscript (v) in that equation as opposed to the usual uppercase (V).|Moemin05 (talk) 13:40, 20 April 2011 (UTC)[reply]

I've just reverted this edit.

For a general audience, it is much more relevant to discuss first what heat capacity means at all in macroscopic terms -- even with the odd equation -- before getting into the microscopic physics of why some substances have the particular values of heat capacity they do at particular ranges.

This distinction -- discussing what the concept means at all first, and what can be said about it macroscopically in full generality -- before getting into any discussion of particular microscopic systems, i.e. the article as it was in its existing form, seems to me by far the more sensible presentation.

But of course, as after any instance of WP:BRD, further discussion and perspectives would be valuable and welcome. Jheald (talk) 18:43, 20 May 2011 (UTC)[reply]

it says extensive. — Preceding unsigned comment added by 131.212.84.146 (talk) 20:51, 6 June 2011 (UTC)[reply]

-> more degrees of freedom or Dulong-Petit not the upper boundary or else ?

The molar mass of water is (2*1,008+15,999)g/mol = 18,015 g/mol. In 1g water are therefore 2*0,055509 mol H-atoms(!) und 0,055509 mol O-atoms.

The maximum value -according Dulong-Petit law- of the specific heat capacity of liquid water is therefore 2*0,055509g/mol*3R +0,055509g/mol*3R = 0,499958g/mol * 8,3145 J/molK =4,154 J/gK. But the real value is 4,18-4,19 J/gK. It's 0,7% bigger!(not much but well above the error boundaries)

What is the explanation of this? (31 October 2006) < I had posted that question 5 years ago. --Bgm2011 (talk) 11:16, 28 August 2011 (UTC)[reply]

I'm very glad to answer your question. I don't know. (Mark Twain). At a guess, since the 3R limit is derived by assuming strictly that ONLY kinetic and vibration-potential energies of atoms are being excited by heat, and these are the only degrees of freedom available, whenever anything goes above 3R/mole of atoms, that is a sign that some other degree of freedom is available to store thermal energy, such as the molecular electronic excitation noted that contributes to the heat capacity of nitric oxide. In liquid water there may be a little of that. SBHarris 23:21, 5 February 2012 (UTC)[reply]

I have a reasonable grasp of science in general, but have forgotten the details of what I learned at school.

I came to this page wanting to discover how to calculate how long my electric kettle should take to boil a cup of water.

The vast majority of the discussion is extremely academic, and having read (or tried to !) through the whole article, I am fascinated by the topic, but I am no nearer to finding out how to do my calculation.

Would it be possible to include a simplified section, giving the basic information, which would be useful to ordinary people who do not have a degree in physical science ?

I think I should be able to read a short way into this article and find a practical formula that I can easily use. Darkman101 (talk) 11:41, 5 February 2012 (UTC)[reply]

The energy delivered by the electric kettle should equal the energy needed to heat up your cup of water. Ask your specific question on Wikipedia:Reference desk/Science rather than expecting this article to answer it. Bo Jacoby (talk) 19:46, 5 February 2012 (UTC).[reply]

The article does have a practical formula, C = Q / ΔT, and we have a data table at the end giving the value of C for water. So that should tell you how much heat per kilogram you need to supply your desired increase in temperature; from which it should be easy enough to work out long you need to run your kettle to supply that heat.

So I think the material needed is in the article. But if people aren't picking up in our article that this is how to use heat capacities, then maybe the article's signposting needs some thinking about. Jheald (talk) 20:22, 5 February 2012 (UTC)[reply]

You're going to have to measure it anyway, since you don't know the efficiency of your kettle. In this example from a consumer, it was 81%. But he had to do the experiment directly anyway, so it didn't help him. If you assumed 100% efficiency, you could have guesstimated the problem and only been 20% off. [1] SBHarris 23:55, 5 February 2012 (UTC)[reply]

Following on JHeald's comment, should we perhaps actually stick C = Q / ΔT in the lede in that form (appropriate for inclusion in a normal line of text), with an explanation of the symbols? I know the text says this in words, but sometimes a formula helps, if it doesn't screw up spacing. WP is not a popular book, in which it is said that every formula will decrease sales by half. Usually we try to keep formulas out of ledes, but if a formula can go into a text line, we might make an exception here. What say you all? SBHarris 20:12, 6 February 2012 (UTC)[reply]

The link to the outdated caloric theory instead takes you to the appliance brand — Preceding unsigned comment added by 58.172.92.222 (talk) 07:48, 29 July 2012 (UTC)[reply]

I have now corrected this. Ulflund (talk) 06:09, 30 July 2012 (UTC)[reply]

"The kinetic energy of substance particles is the only one of the many possible degrees of freedom which manifests as temperature change, and thus the larger the number of degrees of freedom available to the particles of a substance other than kinetic energy, the larger will be the specific heat capacity for the substance." This statement is incorrect, and "kinetic energy" should be replaced with "translation". The kinetic energy of molecules includes all of the motion of atoms (translation, vibration, rotation, stretching, compression, etc.)--El Zarco 03:41, 2 January 2013 (UTC) — Preceding unsigned comment added by ElZarco (talk • contribs)

Yes, it's translational kinetic energy. Will change. SBHarris 04:52, 2 January 2013 (UTC)[reply]

Hi, Just wanted to flag the fact that in the first paragraph: "In the International System of Units (SI), heat capacity is expressed in units of joule(s) (J) per kelvin (K)." I didn't want to edit it because I wasn't completely sure, but isn't it joules per GRAM per kelvin? The formula q = mCΔT can be arranged as C = q/(mΔT)... or C = joules per gram per kelvin.

Thanks! A Wiki Amateur

Bubbathemonkey (talk) 12:00, 7 April 2013 (UTC)[reply]

The formula is correct for heat capacity. You divide by mass to get mass-specific heat capacity (sometimes just called specific heat capacity). A different thing. Read the article, please. Learn something. SBHarris 18:48, 7 April 2013 (UTC)[reply]

The phrase "of a substance" sounds like the language one would use when explaining specific heat capacity, rather than just "heat capacity". Would it be more accurate if we said "...heat required to change the temperature of an object by a given amount"? Spiel496 (talk) 04:18, 8 April 2013 (UTC)[reply]

To put it another way, when someone reads "...heat required to change the temperature of a substance..." their mind jumps to "heat capacity of a substance", which sounds like a material property, i.e. "specific heat capacity", even though that's not what is being defined. Spiel496 (talk) 04:37, 8 April 2013 (UTC)[reply]

Good point. Should say "body" or object or something. Indeed. SBHarris 07:38, 8 April 2013 (UTC)[reply]

Thanks - I learnt something today! I read the units as J/K, then skipped down to the section on units. I had assumed 'specific heat capacity' and 'heat capacity' were the same thing - I didn't even look at the second paragraph. Maybe we could add a 'distinguish' for people like me? Thanks again! Bubbathemonkey (talk) 12:23, 9 April 2013 (UTC)[reply]

We usually have "distinguish" for other articles and sometime ago it was decided to cover both closely related terms in just one (this one). I'll try to add some distinguishing language early to make this more clear. But really, dude, what can you expect if you don't even read paragraph TWO? SBHarris 15:54, 9 April 2013 (UTC)[reply]

Kbrose, what the devil are you thinking? The statement is true for helium gas, but the reason a mole of iron metal has twice the heat capacity of a mole of helium is very simple: half the thermal energy in iron is stored as potential energy of vibration and that doubles the degrees of freedom. So why are you screwing up the lede? I don't have the wrong physics. You do. When I melt ice I do not increase temperature therefore do not increase mean particle kinetic energy. But of course one must increase thermal energy by putting in heat. Therefore thermal energy in this case is in no sense kinetic energy. QED. SBHarris 08:35, 14 May 2013 (UTC)[reply]

First off, Kbrose didn't say that heat capacity is the total kinetic energy, but rather thermal energy is. Second, is one of you (Kbrose or Sbharris) necessarily wrong, or are we just talking about alternative definitions? I can define "XYZZY" to be the "total kinetic energy of a system". It doesn't become right or wrong physics until XYZZY is linked to an experimental result. Self-consistency is the more relevant issue here. I notice that Kbrose's definition is inconsistent with the article thermal energy, which defines the term to include potential energy.

If we do define "thermal energy" to be only the kinetic energy, then, for example, a 1 kg bag of ice water would have the same thermal energy even after most of the ice has melted. Is that definition useful? Is it the conventional one in textbooks? Spiel496 (talk) 01:26, 15 May 2013 (UTC)[reply]

The short answer to your last two questions is no and no.

I will admit that there are subtle problems defining "thermal energy," due mainly to the fact that once heat has flowed into an object, it's a little tricky to say what happened to it. Certainly the heat increases an object's total energy (internal energy), but not all of it sometimes can be recovered again as heat by reversing the thermal contact and cooling, for example if some of it was used to do work (if the object expands and does work, then cooling it again might not recover that energy if the environment doesn't cooperate by compressing it again). So in that case, how can we continue to label that heat energy "thermal"? However, in the absense of PV work problems, most texts do define thermal energy in terms of heat capacity, simply as integral ∫ C(T)dT where C is the heat capacity and T is the temperature. So "thermal energy" is what we used to call "heat content" before we got serious and stopped calling heat "heat" after it had stopped flowing. In that case, half of the thermal energy in solids is not kinetic, but exists as potential energies (again ignoring work).

It might be better not to refer to thermal energy at all in the lede (what is the case now), but if we do, we should surely not use a definition that NOBODY uses. Thermal energy is used in engineering texts now in place of "heat content". The reason being that thermal energy is more or less conserved (in the absense of PV work) in certain heat conduction problems (mostly those in solids and liquids where there is little volume change) SBHarris 02:56, 15 May 2013 (UTC)[reply]

<Quote> while heat is the transfer of thermal energy across a system boundary into the body or from the body to the environment. <unquote> This is risible. Heat is NOT the transfer of ANYTHING. Was this written by a non-fluent English speaker? It is possible that the author meant "to heat" is the transfer of ..." , but why s/he would confuse a noun with a verb is a mystery to me. Nor is it useful. If someone is unable to differentiate things from processes, I suggest they refrain from editing. Heat is a thing, it is a type of energy. According to my old Physics textbook (Physics Pts I & II, c 1966, Halliday & Resnick, pg. 640) "Freeman Dyson, in an article* "What is Heat?" writes:'Heat is disordered energy.' [*Scientific American 1954]". Same text, pg 545 "Heat is that which is transferred between a system and its surroundings as a result of temperature differences only." and "..heat is a form of energy rather than a [material] substance." It is true that heat occurs due to the transfer of energy. But claiming that the transfer of "thermal" energy is heat is mangled logic: thermal energy IS heat. Claiming that the transfer of the thing is the thing would have any Freshman logician tossed out on his/her ear, and rightly so. Please note that the Wikipedia article on Heat makes the same profound blunder, I suspect the same cabal is responsible. Heat energy is not heat flow. If the point is that heat energy is always associated with the transfer of energy, that is fine. Heat is energy. Transfer is not energy. 173.189.78.236 (talk) 01:33, 18 May 2013 (UTC)[reply]

For reasons too complicated to go into here, thermodynamics now defines heat energy only in transfer. Once it stops it is no longer heat, just as a stopped photon is no longer a photon. When heat stops it becomes internal energy. Not thermal energy, as this term is poorly defined, and in any case heat often becomes other types of energy after stopping, like work or chemical energy. There's no point in defining heat as the transfer of a thing when you cannot rigorously define the "thing" as well as you can define heat! Heat is not just energy, though it has energy units. Incremental heating δQ also requires a specific associated entropy change dS = δQ/T. I wish that were true of some quantity we could define as "thermal energy" once it had been transferred, but it isn't. SBHarris 19:04, 23 May 2013 (UTC)[reply]

I agree that the the intro (lead section) needs polishing, and I'm impressed by the writing skill both the above authors and especially the physics textbook author. I think that discussion is so fascinating and BASIC, a short version might belong in the intro? To me "writing skill" is "communication skill." Effective communication is not defined by the words used, but by the rate or quantity of the transfer of desired/useful information. For example...how is the meaning of "red" best communicated? First we need to know what is desired/useful to the reader. A list of true abstract things about red might impress our teachers and peers about how knowledgeable we are, (effectively reciting the answers to an imaginary test,) but will typically do little to explain red to the unknowledgeable. Probably first reciting the wavelength range of 740–620 nanometres, or saying it's the color of light with the longest waves that humans can see, would both be true, but wrong, since there is no "red" without experience/perception, at least for most people. I would first define it with an example such as blood or ripe strawberries, probably both. And Cambridge dictionary agrees. I think heat capacity is such a thing, like Ohm's Law, one can have a gut feeling for the workings of the reality they describe, and numbers for many people are only useful for confirmation or added precision.

I really think the lead needs some examples to pin down all those abstractions. Perhaps water Vs iron Vs...marble?? A whole paragraph! See also: Wikipedia:Manual of Style (lead section). Beware of too many details, and welcome sentences that start with "generally" to portray concepts and general rules, (overviews,)—which is what the lead is all about. Cumbersome rules that enclose the rarities & "exceptions" and the extremely nit-picky or extremely technical, belong in the body where they can be explored in depth. Also beware, I think the lead might already be too technical, have too much jargon for the required "general reader." Thanks!
--69.110.90.19 (talk) 09:23, 27 May 2013 (UTC)Doug Bashford[reply]

Values in the table and in section 'Measurement of heat capacity' are not in agreement. —DIV (137.111.13.36 (talk) 02:54, 30 October 2013 (UTC))[reply]