Talk:First law of thermodynamics/Archive 2

Archive 1

Archive 2

Semi-protected edit request on 21 December 2017

picture 1

A heat engine is a device that generates energy in the form of work by extracting energy in the form of heat from the environment. The heat can come from environmental sources or chemical reactions, and the work produced can be in the form of mechanical energy or electrical energy. The representative heat engine is that develop by Carnot. The Carnot cycle is a mathematical formalism that can`t be achieved in practice, but can be used to understand the operation of real heat engines.

In the Carnot cycle, all processes in the heat engine are reversible, so there is no loss of energy due to its flow. A Carnot engine is a cyclic engine and consists of four processes: two isothermal processes and two adiabatic processes, which operate in the order of isothermal expansion -> thermal expansion - > isothermal expansion -> adiabatic compression. picture 2

In this case, regardless of the gas type, thermal efficiency is as follows. Maximum thermal efficiency=(Q_H-Q_C)/Q_H =1-T_C/T_H The efficiency of the engine defined as the ratio between the heat input and the work-energy output. For example, if the engine draws 100 J from a heat source and uses it to do 60 J of work on the surroundings, the efficiency of the engine would be 60%. The efficiency of a real engine would be lower due to various factors such as the friction of the cylinder piston. To increase the efficiency, the temperature of the high-temperature source (T1) must be high and the temperature of the low-temperature source (T¬2) must be low. Carnot engine is a reversible cycle that changes very slowly but is literally an ideal organ. Actually, it is not possible to completely explain the adiabatic change or isothermal change due to friction or heat conduction, it plays an important role as a kind of comparative value to the actual heat engine. Toacks97 (talk) 00:15, 21 December 2017 (UTC)

@Toacks97:  Not done. This article is for the first law of thermodynamics and your message appears to be a request to make a big edit to either heat engine or Carnot cycle. Please make clear what you believe needs to be improved at this article, how this article is lacking, and where we should add your text. CityOfSilver 01:22, 21 December 2017 (UTC)

Semi-protected edit request on 14 February 2019

CHANGE "The first law of thermodynamics is do not talk about thermodynamics. a version of the law of conservation of energy, adapted..." TO "The first law of thermodynamics is a version of the law of conservation of energy, adapted..." Elzaidir (talk) 10:16, 14 February 2019 (UTC)

 Done DannyS712 (talk) 10:22, 14 February 2019 (UTC)

Fiducial reference states??

Please clarify the meaning in thermodynamics of the word "fiducial" and the clause "With due account of the respective fiducial reference states of the systems, ..." Dirac66 (talk) 01:40, 23 November 2019 (UTC)

Fair question. I saw the word 'fiducial' used in this way and thought it seemed helpful. I am not wedded to it. It just seems to emphasise how much care needs to be taken in respect to the reference states. Sorry, I can't rememer where I saw it. I will remove it.

What does the clause mean? It emphasises that if two bodies have different chemical compositions, they don't share a common reference state for stating U. One needs a system for setting compatible reference states. You will be familiar with the customary system. I would be happy with a better way to express this.Chjoaygame (talk) 05:59, 23 November 2019 (UTC)

Perhaps it would help to explain the various reference states involved for a specific example, such as the evaporation process mentioned in the section "Process of transfer of matter between an open system and its surroundings". Dirac66 (talk) 01:57, 24 November 2019 (UTC)

I had more in mind, for example, a combining of a system consisting of anhydrous salt with a system consisting of water. They don't have a mutually common reference state. A way to deal with this is to take every system back to a combination of systems consisting of pure elements in standard reference states. Then one can list the several constituent elementary systems and states as references. Would that be ok? I didn't put such detail in the lead because it seemed complicated.Chjoaygame (talk) 10:24, 25 November 2019 (UTC)

Yes, your salt-water example is better as it involves two different compounds. And no, I wouldn't put all this in the lead. Rather a new (sub)section further down, perhaps after Spatially inhomogeneous systems or Open systems. Dirac66 (talk) 11:54, 25 November 2019 (UTC)