# Talk:Isothermal process

WikiProject Physics (Rated Start-class, Mid-importance)

## Is PV=NRT a linear transformation? Or an integral function?

In T.W.,students uiversally accept concepts of PV=NRT being taught by teachers in class affording to juge a thermo-process's kind.

I truely think that it is rediculous. Because of they ingnore much more details about something like

${\displaystyle ({\frac {\partial {V}}{\partial {T}}})_{p}({\frac {\partial {P}}{\partial {T}}})_{v}}$.

(Note:one formula exists three viriables(functions),and parts of them play dilute roles: constants and functions)

Some students in my country(Taiwain) do not realize very much about PV=NRT as a linear transformation whether really do. If we observe a small region d(PV), it represents work done by a system. But we can not immediately concluse as

PdV+VdP=nRdT

Generally speaking,it is accepted only two viriable numbers in a function of thermodynamics. And more meaning of that is how we ensure dT whether belongs a group of molecules' performance of average kinetic energy or a infinite small temperature observed on a scale? --HydrogenSu 17:41, 19 December 2005 (UTC)

better if we write
PdV + dPV=nRdT +dnRT Srijan Suryansh talk (ping me if you have birthday on 27/7/3.)) 17:28, 4 June 2021 (UTC)

## delta U = q + w

While the magnitude of work and heat are equal for an isothermal process, the signs are different. So for an isothermal expansion, work is done by the gas (system) on the surroundings and the sign is negative by definition, but heat is absorbed by the gas and the sign is positive. Similarly, for an isothermal compression, work is done on the gas (system) by the surroundings and the sign is positive, but heat is given off from the system to the surroundings and the sign is negative.

Someone please fix this. Mdewman6 (talk) 05:29, 10 March 2009 (UTC)

## dU = 0

Hi- I believe dU = 0 for an isothermal transformation only holds in particular cases (namely that of an ideal gas) and not for all systems. —Preceding unsigned comment added by 76.171.215.133 (talk) 00:38, 3 May 2009 (UTC)

• Yes, ΔU = 0 for ideal gases, but not for real gases, due to intermolecular forces. Thanks for catching this error. - Astrochemist (talk) 13:15, 3 May 2009 (UTC)

## Possible inconsistency in applications section (internal temperature changing in isothermal process)

In the "Applications" section, the last sentence currently reads:

"So if the real pure gas undergoes an Isothermal process, there is a net change in internal temperature consistent with this component of internal energy.[1]"

This looks inconsistent with the definition of an isothermal process. Can someone who understands these issues well confirm, and delete or clarify if appropriate?

MorphismOfDoom (talk) 03:27, 5 June 2013 (UTC)

I fixed the sign error. But the section is still rambling and largely duplicates the previous section. Retired Pchem Prof (talk) 18:34, 17 February 2016 (UTC)

## Calculation of work

I have made a number of corrections to this section. As noted by others above, the sign convention for work was not consistent; I fixed that. I specified that the equation for PV work is for reversible work; the general equation uses the external pressure. I specified ideal gas as required. I corrected the last paragraph as appropriate for the adiabatic process. Retired Pchem Prof (talk) 18:26, 17 February 2016 (UTC)

## Examples (was "Applications")

I moved this section, which was very general, to before the more detailed sections. I gave it a more appropriate heading. Sadly, I did not check if the change in heading would mess up any links; I did not think of that until just now and would not know how to check anyway. I rearranged the paragraphs from most general to least general. I tightened up the text throughout. I removed details that duplicate those in "calculation of work". I changed "perfect gas" (used in kinetic theory) to "ideal gas" (used in thermodynamics). I added some links, but have yet to add references. Retired Pchem Prof (talk) 20:20, 18 February 2016 (UTC)

## Entropy Changes

I have created this section discussing entropy changes in some isothermal processes, both reversible and irreversible. Perhaps there could be some references added in the last two paragraphs, but they would just be more ibids and op cits. Retired Pchem Prof (talk) 01:43, 18 March 2016 (UTC)

### Example of an isothermal process

I created this sub-section to clarify the arithmetic for calculating the way overall work is distributed.Thermbal (talk) 03:11, 12 January 2019 (UTC). its so easy