Talk:Heat capacity

Units

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)

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)

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)

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)

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

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)

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)

Hi, I had exactly the same issue, and even created a wikipedia account for that. I often use it just to look up units. I think an information which is so likely to be missed should be in the first paragraph, or at least clearer in the section "units" below. I only looked at units, and only found it when seeing the one in the "Measurement" section even further down. S 14:59, 3 October 2017 (UTC)

Hi, This page kept getting me confused over and over again, and finally I understand where my confusion comes from, yet I didn't want to edit directly. I have no formal physics or chemistry education, and even more to my disgrace, this is my first Wikipedia edit. Therefore I chose to add my remarks to the discussion with hopes that someone more knowledgeable can verify my claims and fix the errors.

In the introduction (first paragraph), heat capacity is described and then the units are for specific heat capacity. It is also inconsistent with the dimensional form in the same paragraph (T⁻²L²MΘ⁻¹), which I believe is correct for heat capacity, but not for specific heat capacity. I tracked this error to a recent [1]. It was even more confusing because later, in Extensive Properties, it is defined correctly, but nowhere else are **specific heat capacity**'s units described. Oranjax (talk) 12:36, 13 December 2016 (UTC)

Definition of Heat Capacity

Can anyone explain to me why we have the current definition of heat capacity, C=ΔQ/ΔT? I know that some texts use this or a similar expression as the definition of heat capacity, but I've never liked it. To me, the Δ's imply a discrete change and that heat capacities are constants when, in fact, they are highly temperature dependent. Also, I don't like the ΔQ term as it implies that Q (heat) is a state function, which it is not. Would people be OK with changing the definition to C=δq/dT. Changing to an infinitesimal change helps solve the problem of C=C(T) an the use of δ implies an inexact differential, which is the same notation used in most of the article. JCMPC (talk) 20:23, 22 January 2014 (UTC)

You make a good point. Even if we don't go all the way to "C=δq/dT" we should at least say "Q/ΔT" so that heat doesn't look like a state function. Spiel496 (talk) 02:24, 23 January 2014 (UTC)

I wholeheartedly agree. Why has the definition not been changed to "Q/ΔT", yet? Are there any defenders or the current formulation who would like to weigh in? — Preceding unsigned comment added by 2A01:C50F:9D4A:5500:C884:7819:1534:5966 (talk) 12:17, 19 February 2021 (UTC)

Very good point. The quantum expression of the heat capacity is mutch more elusive. I try to reform the molecular orbital theory and it's almost impossible to make an intelligible text about it. It must be filled with simple unnacurate physical equation because I think it's out of the realm of humans logic and something that only computer can do. The expression is $$C \ind(V,m)= \frac(1,2)\times(3 + v_R^* + v_V^*)R$$ 70.81.186.183 (talk) 16:21, 22 October 2016 (UTC)

Magnetocaloric effect

Magnetocaloric effect is a nice way of showing how degrees of freedom and temperature relate; (gadolinium in and out of strong magnetic fields). see: https://en.wikipedia.org/wiki/Magnetic_refrigeration maybe add it as a link or use as example. 71.139.161.30 (talk) 23:43, 3 December 2016 (UTC)

Degenerate matter

What is the heat capacity of degenerate matter? What should be entered into an equation to model the cooling of a white dwarf, for instance?

2600:1700:4CA1:3C80:C8D2:18ED:2941:6B2D (talk) 01:05, 6 August 2018 (UTC)

Time to split "specific heat" off from this article

I tried to clean up this article, but it is still way too long and jumbled. It is not serving its goal -- informing the typical reader who needs to know about the topics covered.
The biggest problem is the attempt to cover "heat capacity" (extensive) and "specific heat" (intensive) in the same article. It would be like having a single article for "mass" and "density", for "distance" and "speed", for "planet" and "mineral"...
While related, they are quite distinct concepts, and deserve their own separate articles. There is very little that would need to be shared by both articles. From examples to theoretical "ab initio" computations, most of the material is specific to only one of those two topics. (And some material, like the units of measurement of heat, should be moved to the heat article instead.)
Moreover, other articles that need to link to "specific heat" now must link to a section of this one (or maybe two or three widely separate sections!), which probably do not give the reader the desired information...
Unless there are good arguments to the contrary, I intend to do the split next week, myself.
All the best, --Jorge Stolfi (talk) 06:47, 12 April 2019 (UTC)

I disagree. The article can be shortened in other ways, nobody needs, nor reads, all the formalism. Algebraic exercises don't belong in a general purpose encyclopedia. Kbrose (talk) 22:14, 8 May 2019 (UTC)

I fully agree that algebraic derivations and proofs should not be given (unless the derivation itself is the topic of the article, which is not the case here). I will try to do that cleanup too.
But that is a separate issue.
I noticed that the articles were once separate, but were merged without sufficient discussion and without a valid justification. That was a mistake, because there are four clearly distinct concepts here. Since Wikipedia is meant to be a reference work, not a textbook, distinct concepts should be put in separate articles. That will be better for readers who are looking for information in one of those concepts, and better for editors who have to link to it. --Jorge Stolfi (talk) 23:49, 10 May 2019 (UTC)

That is not convincing, and the topics are not distinct. Please seek wider consensus first. Kbrose (talk) 02:25, 11 May 2019 (UTC)

The article ias a mess, as you say, and has not been improved in TWO YEARS. The split request has been posted for one month. You have been the only one objecting to the split, with no real arguments (in fact, you only commented about the derivations, not the split itself).
If you don't have the time to improve the article, at least do not prevent others from doin so.--Jorge Stolfi (talk) 03:24, 11 May 2019 (UTC)

Don't put words into my mouth. Splitting the article is not improving it. There is no didactic reason to split the topic, and it just causes a lot of duplication of similar reasoning and formalism. If ever, the article was apparently at least more stable in the combined form than previously. At least one article, this article, should provide the comprehensive overview of the subject matter. Kbrose (talk) 12:24, 11 May 2019 (UTC)

The "didactic" reasons to split the article are obvious, in fact. A reader who needs to know what is specific heat should not have to wade though a discussion of molar heat capacity or volumetric heat capacity, and vice-versa. There may *seem* to be duplication, because the topics are *similar* -- but quite different in crucial details. (And "didactic" is not quite the right word. Wikipedia is meant to be a reference source, not a textbook.).
I am still not done; the mess was huge. Please wait a few more days beore deciding whether it was an improvement or not. --Jorge Stolfi (talk) 03:59, 14 May 2019 (UTC)

I fail to see how dividing by mass/moles/volume is really worthly of a different page. If that was true, then we would need a page in CGS units, and one in metric units, and one in fairy dust units.... AManWithNoPlan (talk) 22:07, 13 May 2019 (UTC)

Mass, moles, and volume are not just different units! They are different physical quantities. Specific heat and molar heat capacity are like people per square mile and population per country. Molar heat capacity is not even defined for many substances, whereas specific heat is. --Jorge Stolfi (talk) 03:59, 14 May 2019 (UTC)

Perhaps we need separate simple pages for each, and then a single huge "theory of heat capacity" page that they all link to if you need to understand energy levels, etc. AManWithNoPlan (talk) 15:46, 14 May 2019 (UTC)

That apparently was the idea of the unsplit article. However there does not seem to be such a thing as a "theory of heat capacity". Instead there are:

1. Some general properties of heat capacity of general objects such as additivity. However, the heat capacity cannot even be defined for general thermodynamic systems, and the C_P x C_V discussion is very limited. (Consider a gas enclosed in a metal can with tops that can bulge out under pressure.)
2. A theory for the specific heat of relatively homogeneous substances where one can define c_P and c_V and relate them to the equation of state and the internal energy function of the material. This theory can be applied to any homogeneous gases, liquids, or solids, including solutions, substances with unknown molecular size (like polymers) and aggregaes that are homogeneous only at a macroscopic scale, such as milk, clay, concrete, sand, etc.. It could even be extended to non-isotropic materials.
3. A theory for the molar heat capacity of subtances with well-defined composition, homogeneous at the molecular scale based on the notion of molecular/atomic degrees of freedom. This theory can be applied to gases and (not very dense) mixtuers thereof, and (separately) to solids that are homogeneous enough for the density of DoFs to be defined.

While the last two theories are connected, their exposition is largely independent. Thus they fit well in the respective articles. (Theory 2 is currently in heat capacity but I intend to move it right away to specific heat capacity since both apply to the same class of materials.)
All the best, --Jorge Stolfi (talk) 06:13, 15 May 2019 (UTC)