# What is Thermodynamic: Definition and 500 Discussions

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.
Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of French physicist Nicolas Léonard Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency."
The initial application of thermodynamics to mechanical heat engines was quickly extended to the study of chemical compounds and chemical reactions. Chemical thermodynamics studies the nature of the role of entropy in the process of chemical reactions and has provided the bulk of expansion and knowledge of the field. Other formulations of thermodynamics emerged. Statistical thermodynamics, or statistical mechanics, concerns itself with statistical predictions of the collective motion of particles from their microscopic behavior. In 1909, Constantin Carathéodory presented a purely mathematical approach in an axiomatic formulation, a description often referred to as geometrical thermodynamics.

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1. ### Thermodynamic Work vs Mechanical Work

At first I thought these values should be equal because I thought thermodynamic work is simply the work done as the gas compresses or expands. That is, the work done as the gas expands ( and the mass gets lifted up) should be equal to the work done against gravity as the mass goes up, and the...
2. ### Thermodynamic equilibrium for systems only open to particle exchange

I am only interested in the initial equilibrium conditions, and I am struggling to convince myself whether that should correspond to the equality of chemical potentials for H2 or an equality of temperatures as well. My work is as below: We take both gases as simple ideal (this is only relevant...
3. ### Misc. Bernoulli effect on new vent design

First off don't quit reading if you understand basic Bernoulli effect. I am nowhere close to the caliber of minds on this forum but I have a problem and lack understanding that science may help answer. Preface: Temperature extremes are stressing wildlife populations. I happen to be an advocate...
4. ### Concept of Absolute Thermodynamic Activity

In the textbook Electrochemical Systems by Newman and Alyea, Chapter 14: The definition of some thermodynamic functions, chemical potential of component (ionic or neutral) is written as a function of absolute activity: $$\mu_i=RT\ln(\lambda_i)\tag1$$ where ##\lambda_i## is the absolute activity...
5. ### Calculate these 5 temperatures along this Thermodynamic cycle

I only know T3 = 4•T1 I was able to calculate the T2 = Tb = T4 I built four equations: T2 = p2V1 / nR T4 = p1V2 / nR p1/T1 = p2/T2 V1/T2 = V2/4T1 I put them together and got T2 = 2T1 I can't figure out the temperatures of A and C. I tend to think Ta could equal Tc (then I would be able to...
6. ### B Understanding thermodynamic equilibrium

My thermodynamics is rusty and my current endeavors demand me to wield it, so here we go: I need a good starting point and/or references to study physical systems in thermodynamic equilibrium. Any references which address the fluid mechanics perspective of said systems are welcome too. Let me...
7. ### What is the relationship between entropy and pressure in thermodynamics?

Hi, Starting from dS in term of H and P, I'm trying to find ##(\frac{\partial H}{\partial P})_t## in term of ##P,V,T, \beta, \kappa, c_p##. Here what I did so far. ##ds = (\frac{\partial S}{\partial H})_p dH + (\frac{\partial S}{ \partial P})_H dP## ##ds = (\frac{\partial S}{\partial H})_p [...
8. ### B How are thermodynamic laws related to one another?

Would you please explain how the laws of thermodynamics are related to one another? Are the laws entirely independent of one another? I can see only a connection between the zeroth law and the second law. Following is the quote from my previous thread. 1. Zeroth law: The zeroth law of...
9. ### I Minimization of thermodynamic equilibrium

Hi, I don't understand what does it mean that at equilibrium the proper thermodynamic potential of the system is minimized. For example on the book Herbert B. Callen - Thermodynamics and an Introduction to Thermostatistics it is written: Helmholtz Potential Minimum Principle. The equilibrium...
10. ### I Thermodynamic constant -- misunderstanding

I was reading about thermodynamics in my textbook wheni came across the following thermodynamics constants: However, i don't understand why did we define 1/V inthe constants. What is the point in doing this?
11. ### Thermodynamic Cycle -- Work done as a function of Heat absorbed

During a thermodynamic cycle, an ideal thermal machine absorbs heat Q2 > 0 from a hot source and uses it to perform Work W > 0, giving a cold source a heat Q1 < 0 with an efficiency of 20% . How much is the work done as a function of Q1 ?I have 2 question regarding this problem: 1) Why is Q1 the...

13. ### Change of entropy in the Universe in a thermodynamic cycle

(a) We first find that: ##T_A=\frac{P_A V_A}{nR}=\frac{1\cdot 10^5 \cdot 4}{40\cdot 8.314}K\approx 1202.7904 K##, ##\frac{T_B}{T_A}=\frac{\frac{P_B V_B}{nR}}{\frac{P_A V_A}{nR}}=\frac{P_B V_B}{P_A V_A}=\frac{P_A \frac{V_A}{2}}{P_A V_A}=\frac{1}{2}##, ##\frac{T_C}{T_B}=\frac{P_C...
14. ### I Understanding the Clausius-Clapeyron Formula: V_{l} and V_{g}

Hey, I have a question about the meaning of a variable in the Clausius-Clapeyron formula. My textbook (Daniel v. Schroeder) says that the Clausius-Clapeyron formula is (for phase boundary between liquid and gas) \frac{dP}{dT} = \frac{L}{T\left(V_{g} - V_{l} \right)} . What is V_{l} or V_{g}...
15. ### I Understand the Thermodynamic Identity: Is This Correct?

I have a question about the Thermodynamic Identity. The Thermodynamic Identity is given by dU = TdS - PdV + \mu dN . We assume that the volume V and that the number of particles N is constant. Thus the Thermodynamic Identity becomes dU = TdS . Assume that we add heat to the system (we see that...
16. ### Thermodynamic and mechanical work

What is the difference between thermodynamic and mechanical work? Should they show equal values in an experiment? If yes, what possible errors could cause if there is a difference in their values?
17. ### A Vacuum Flask Thermodynamic Equation

Im trying to find an advanced thermodynamic equation for a vacuum flask. I am looking for an equation to find the temperature of a liquid at time t as it cools down. Ignore the cap and bottom section; assume there is no heat loss in those areas. I'm just interested in the cylindrical...
18. ### Recognizing Thermodynamic Scenarious (Work Done)

Let me start out by saying it's been a LONG time since I've touched any thermodynamics but I'm starting to think that the answer for all 3 parts are the exact same (at least for work) Namely ##W = \int_{\frac{L^3}{2}}^{L^3} P(V) \, dV = NkT_0 \int_{\frac{L^3}{2}}^{L^3} \frac{1}{V} \, dV =...
19. ### I Comparing Spacetime and Thermodynamic State Space Manifolds

Hi, I don't know if it is the right place to ask for the following: I was thinking about the difference between the notion of spacetime as 4D Lorentzian manifold and the thermodynamic state space. To me the spacetime as manifold makes sense from an 'intrinsic' point of view (let me say all the...
20. ### I Thermodynamic functions and state variables

Hi, a basic doubt about thermodynamic functions and state variables. Take for instance transformations I and II in the following ##(p,V)## plane. As far as I can tell, just because the transformations are drawn as continuous lines they are reversible by definition. Namely we can transform...
21. ### I Thermodynamic Pros/Cons coating light metal tanks with rubber

Hi Folks, I promise there is an actual question at the end of this note. I couldn't see where to attach images on this forum page, so here is a link to a rough illustration and a photo of the project site in progress (the cabinet for the digester is partially built)...
22. ### Thermodynamic Axioms: Establishing Temperature, Internal Energy & Entropy

Is the purpose of the 0th, 1st & 2nd Laws of Thermodynamics simply to legitimate the thermodynamic properties of Temperature, Internal Energy & Entropy, respectively? It seems that all these laws really do is establish that these properties are valid thermodynamic state properties and the...
23. ### A Wave Function Collapse and Thermodynamic Irreversible Processes

Very early in the development of thermodynamics, it was realized that the 2nd Law of Thermodynamics is not a law fundamental to the fabric of our cosmos, but only becomes true in the limit of the number of particles. It was none other than Boltzmann himself who realized and articulated this...
24. ### Net heat in a thermodynamic cycle

In AB, dU=0 (Isothermal) Hence dQ=dW W1= RT ln(2V/V) = RT ln(2) = 800R*ln(2) Q1=W1 = 800R*ln(2) Q2= Cp(300-800)=-500Cp = -500*2.5R Q3 = Cv(800-300) = 500Cv = 500*1.5R So Q= 800R*ln(2) -500*2.5R + 500*1.5R = 800R*ln(2) -500R Hence net heat absorbed is 800R*ln(2) -500R But. Suppose I find...
25. ### Efficiency of a heat engine given a P-V diagram of its process

I post the working in the attached file
26. ### Manipulation of a Thermodynamic Relation

##(\frac {∂p} {∂ρ})_s=ϒ(\frac {∂p} {∂ρ})_T## The variables are p for pressure, ρ for specific mass density and γ is ratio of specific heats. I am able to show that the relation is valid for a perfect gas but cannot show its validity in general. The closest I get is ##dp=(\frac {∂p} {∂ρ})_s...
27. ### The work done by Thermodynamic processes

Hi gentlemen I want to know the classification of thermodynamic processes according to which is higher than which in work done during either compression or expansion. Thermodynamic processes like isentropic and isobaric. Thanks
28. ### Thermodynamic meaning of molar Gibbs free energy

I know that when it is ΔG>0 , it means there is no spontaneity, when ΔG=0 there is equilibrium, and when ΔG<0, there is spontaneity. But what happens when this is in the context of partial molar properties, when G is molar? I suppose molar ΔG is referred to a solution. Right? In that case, is...
29. ### Find the value of Cp using SFEE and Thermodynamic equations

I have managed to find the gamma value using the following equation: (T2/T1)= (P2/P1)(gamma-1/gamma. This will give me the answer of 1.29 SF. After this step, I am clueless. Can someone help me with this question please? I assume we have to find the enthalpy at state 1 to do that question.
30. ### Proof question related to the Ideal Gas Law

A cylinder contains an initial volume V1 = 1m^^3 of a perfect gas at initial pressure p1 = 1 bar, confined by a piston that is held in place by a spring. The gas is heated until its volume is doubled and the final pressure is 5 bar. Assuming that the mass of the piston is negligible and that the...
31. ### Does a Well-Defined Entropy Exist for Non-Ideal Gases A and B?

The conclusion of my attempt I am listing below is that there do exist entropies for both but I am not sure. $$dU=TdS-pdV$$ $$dS=\frac{dU}{T}+\frac{p}{T}dV$$ Therefore, gas A: $$S=\frac{{\Delta}U}{T}+\alpha_A(\frac{-N}{{\Delta}V})$$ Gas B...
32. ### Physicists build Graphene Thermodynamic Battery

I read an article in Science Daily 'Physicists build circuit that generates clean, limitless power from graphene'. Can someone explain how to take this from the physics science experiment to the engineering prototype and implementation stage? Is this technology going to revolutionize the mobile...
33. ### Engineering First law of a thermodynamic system

After crossing out all the variables which I think equals 0 in the equation, I was left with: ∆PE + ∆U = Qin mg (0.2) + ∆U = 300 10*9.81*0.2 - 300 = - ∆U = -280J This was the answer I derived. However, the correct answer was supposed to be 123.3J. Please can someone explain to me how to get...
34. ### B Can spontaneous emission be considered a thermodynamic process?

I realize that nothing causes an excited atom to emit a photon, and that it's a random process. But someone was asking me about why energized systems in general tend to lose their energy to the environment and move toward equilibrium. I mentioned that an inflated balloon, given a hole, will tend...
35. ### How to derive this thermodynamic math identity

So the Legendre transforms are straightforward; define ##S_1=S-\beta E## and ##S_2= S-\beta E + \beta \mu n## then we get: ##dS_1 = -Ed\beta - \beta \mu dn + \beta PdV## ##dS_2 = -Ed\beta + nd(\beta \mu) + \beta PdV## And so by applying the equality of mixed partials of ##S_1## and ##S_2## we...
36. ### Thermodynamic identity (math) question: one component system

I was just wondering what is wrong with the following logic; From the Gibbs-Duhem relation we get, ##\frac{\partial \mu}{\partial P}\Big\rvert_T = v## Now consider, ##\frac{\partial v}{\partial \mu}\Big\rvert_T = \frac{\partial }{\partial \mu}\Big (\frac{\partial \mu}{\partial P}\Big\rvert_T...
37. ### Thermodynamics: Single/Homogeneous Phase Differences

#Can somebody please explain what is the difference between single phase and homogeneous phase in context with thermodynamics? #Also in the fundamental relations in thermodynamics like dg=vdp-sdT , it says this is applicable to homogeneous phase of constant composition. Isn't this equation...
38. ### Thermodynamic process and entropy -- Two chambers with different gasses with interconnecting membranes

We need to find the system's entropy variation. I don't think i understood pretty well what is happening in this process, can someone help me how to start?
39. ### Reversible Otto Cycle Efficiency: Investigating the Difference from Carnot's

So we know that every reversible engine working between the same temperatures will have the same efficiency(the same as Carnot engine). So let's consider for example reversible Otto cycle. So as you can see on the picture it is operating between ##T_1## and ##T_3##, so I was thinking that it...
40. ### Chemistry Calculate the boiling temperature of methanol from thermodynamic data

Calculate the boiling temperature of methanol at 60 atm knowing that Tc = 513K, Pc = 78 atm and the acentricity is 0.555. I would like you to help me start the exercise. I thought about using the Pitzer Correlation to be able to calculate the fugacity coefficient, but I don't have the...

42. ### Gas in a syringe being compressed - thermodynamic processes

1. Adiabatic compression (When compressed quickly, there is no heat flow to the environment Q=0) Isochoric with heat loss (The syringe is still compressed, there should be no change in volume) Adiabatic expansion (When the syringe is released, there is work done only) Isochoric with heat gain...
43. ### Thermodynamic equation of differentials (and how to work with them)

Disclaimer: I am not a mathematician, I am a physicist. The thermodynamic identity is usually expressed in the following differential form $$dU = TdS - PdV + \mu dN,$$ where U , T , S , P , V , \mu and N are the internal energy, temperature, entropy, pressure, volume, chemical...
44. ### Thermodynamic state having 2 degrees of freedom (i.e., for properties)

I'm trying to delve into the reason why this is so. It seems that there are 5 fundamental properties: P - Pressure V - Volume (specific) T - Temperature S - Entropy (specific) U - Internal Energy (Yes, there are other types of energy, but they are fully determinable from these 5 - e.g...
45. E

### Thermodynamic sign convention for heat (i.e. in heat engines)

Just to clarify, I'm aware of the two equivalent expressions of the first law ##\Delta U = Q + W## and ##\Delta U = Q - W## when applied to a certain system, though my question is primarily about ##Q## - for which, as far as I am aware, the convention is almost universally that ##Q > 0## if heat...
46. ### Partial derivatives of thermodynamic state functions

I'm in a first-year grad course on statistical mechanics and something about multivariable functions that has confused me since undergrad keeps popping up, mostly in the context of thermodynamics. Any insight would be much appreciated! This is a general question, but as an example imagine...
47. ### Thermodynamics: calculate thermodynamic derivative from data?

I don't understand how to use output from an NPT molecular dynamics simulation to compute a thermodynamic derivative. I need to compute this (where "d" is a partial derivative, "T" is a subscript that means, "at constant temperature," and "E" is internal energy): -(dE/dV)T I have a simulation...
48. ### Relation for the thermodynamic and transport properties of Methanol

I need to find the properties such as specific heat capacity, thermal conductivity, density and others.
49. ### What is the role of heat and pressure in a slow thermodynamic process?

Dear experts, Considering a cylinder and a piston where the volume is V and the pressure is P and the temperature being T, the gas is slowly allowed to expand accepting heat keeping the temperature constant at T to twice the volume. The pressure according to the ideal gas equation should go...
50. ### Thermodynamic properties of compressed liquids

Hi All, I have review my thermodynamic notes (~35 year ago..), and I could not able to restore how to get thermodynamic properties (u,h,s,v ..) for compressed liquids. I have found properties tables for compressed liquids ( for water..) but unfortunately the data starts at 5MPa. What if I look...