What is Thermodynamics: Definition and 996 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. MatinSAR

    Recommendation for project related to thermodynamics

    TL;DR Summary: I'm currently studying physics (undergrad level). I want to find a project related to thermodynamics to present it to my professor. I am reading this book: Heat and Thermodynamics: An Intermediate Textbook by Mark Zemansky and Richard Dittman...
  2. Q

    B Are wind farms stealing the cooling capacity of the wind?

    Hi, this is a atmospheric physics question. When the sun heats up the ground (dark granite slab/asphalt), makes a thermal column of air rise, gradually accumulating into a higher pressure area, and then wind, when it moves from higher pressure to a lower pressure area, it is distributing the...
  3. cianfa72

    I State equations for a thermodynamic substance/system

    Hi, as follow up to this thread I believe for any substance/thermodynamic system there exists actually a set of 3 state equations between the 5 variables ##(U,T,S,p,V)##. For example in the case of ideal gas which are the 3 equations ? Thanks.
  4. E

    Interesting question: heating a metal wire

    I have attached a PDF file.
  5. Karfen

    Thermodynamics homework -- Estimate the molar specific heat of the air at constant volume Cv

    And this is the Cv graph for hydrogen: I think the Cv graph for air is similar with this graph. But I don't know the answer, can someone tell me?
  6. Z

    I Graphical difference between adiabatic and isothermal processes.

    Let me first get through a few calculations to set up the main part of this question. From the first law, we have that $$dQ = dU - dW\tag{1}$$ Now, we also have $$dU=\left (\frac{\partial U}{\partial T} \right )_VdT + \left (\frac{\partial U}{\partial V} \right )_T dV\tag{2}$$...
  7. Z

    I Why does an ideal gas satisfy ##(\partial U/\partial P)_T=0##?

    The book I am reading says that by definition, the ideal gas satisfies the equations $$PV=nRT\tag{1}$$ $$\left (\frac{\partial U}{\partial P}\right )_T = 0\tag{2}$$ where does (2) come from? In other words, what justifies this equation in the definition above?
  8. Z

    I Where are the limits being taken in these thermodynamics equations?

    Here is a passage from a book I am reading My question is about the limits. Are all the limits in the derivation above done for ##P_{TP}\to 0##? In particular, is it ##\lim\limits_{P_{TP}\to 0} (Pv)## that appears above? The author omits this information in all but the first limit and it...
  9. Z

    I How to measure average thermal conductivity of a metallic material?

    Heat conduction is the transport of energy between neighboring volume elements in a material as a result of the temperature difference between them. The "fundamental law of heat conduction", as it is called in the book I am reading, is a "generalization of the results of experiments on the...
  10. W

    Classical Physics books for me!

    Hi,I m studying for college and I need to receive some info from you guys. Which books should I use to study mechanics,thermodynamics,electricity and magnetism? I have no idea what books I should study because my own physics teacher has some pdfs in her USB and I can t borrow the USB because...
  11. K

    History - Evolution of ideas in the field of thermodynamics (statistics in mechanical and gas dynamics)

    Hi, I have a question regarding the evolution of idea in the field of thermodynamics. Boltzmann is genereally credited with the notion of stasticis and it's relation to entropy. However, Boltzmann was inspired by the work of Maxwell (who himself followed the conceptual models of Bernoullli for...
  12. A

    I Application of the first law of thermodynamics

    In Halliday's physics book, there is an example of the first law of thermodynamics that shows its application. The figure below explains this example: Here is a question, if the element alone is chosen as the system, doubts arise in the first law, because in this system, Q<0 (because heat is...
  13. Z

    Work done in a chamber with gas undergoing adiabatic free expansion?

    Let's consider the system as both internal chambers together, ie everything inside the adiabatic walls. We have ##Q_{sys}=Q_{gas}+Q_{evac}=0## because we have adiabatic walls and ##W_{gas}+W_{evac}=0## because of the rigid walls. ##\Delta U = U_f-U_i=Q_{gas}+Q_{evac}+W_{gas}+W_{evac}=0##. How...
  14. Z

    I How to understand experiment to measure heat capacity of solid?

    Consider the problem of measuring the heat capacities of solids using an electrical method where a resistance wire is wound around a cylindrical sample of the material. Why and how is the dissipated energy in the first case considered work and not simply an internal exchange of heat (which...
  15. Z

    What is the problem with the units in this state equation of a gas?

    My question is about units. For the first part, we can solve the state equation for ##P## as a function of ##V## and ##T##. We obtain $$P(V,T)=\frac{RT}{V-b}-\frac{a}{V^2}\tag{1}$$ The units question already comes up here because as far as I can tell the right-hand side doesn't have the...
  16. anjauk2003

    Chemistry Calculate the pressure-volume work for the given reaction

    I dont have an solution Attempt. Maybe something with PV=nRT but this is for ideal gas and H2O is liquid. An other formula they introduced us to is: dE=-P*V
  17. Z

    Work done during quasi-static, isothermal expansion from P_i to P_f

    I am posting this question after I thought I had easily solved the problem, but then when I checked the back of the book I saw that I was incorrect. Here is what I did. (a) $$W=-\int_{V_i}^{V_f} PdV\tag{1}$$ $$V=V(P,T)-\frac{nRT}{P}\tag{2}$$ $$dV=\left ( \frac{\partial V}{\partial P}\right...
  18. Z

    Work done on container receiving gas from high pressure container

    It seems to me that we can already answer b): if gas leaks from the high pressure container to the atmosphere, there is no expansion work. The container loses gas, which means in ##PV=nRT## we have ##n## going down and ##P## going down, and perhaps ##T## going down. But no work. As for a), I...
  19. Z

    I Work in hydrostatic system in cylinder with piston: P_int or P_ext?

    I'd like to show two different ways of defining work in a hydrostatic (PVT) system in a cylinder with a piston. One way is in a book that I have slowly come to hate: Physical Chemistry by Silbey, Alberty, and Bawendi. In that book, work is defined using the external pressure on the piston...
  20. Z

    Log-log graph of resistance against temperature for a carbon resistor

    (a) (b) Here is a plot of this function T of R It seems that as the resistance goes up the temperature goes down. Not sure what to make of this physically speaking. My question is about the requested log-log graph. Above we have a function T of R, but we want a function ##\log{T}## of...
  21. Z

    Calculate ideal-gas temperature of a material

    Here is the table As far as I can tell what we have here are four constant-volume thermometers (each column represents a thermometer). These thermometers work by having a certain constant volume of some specific gas in a bulb. We immerse the bulb in whatever temperature we would like to...
  22. Z

    I Constant length metallic wire as a thermometer, using tension?

    I posted another question about a thermodynamic system with three coordinates, namely, that of a metallic wire. We can describe that system with temperature, wire tension, and wire length. The result derived in that question was that the partial derivative of wire tension relative to absolute...
  23. Z

    I Partial derivative of wire tension relative to temperature, holding wire length constant.

    I have a question about a derivation I saw in the book "Heat and Thermodynamics" by Zemansky and Dittman. A "sufficiently complete" thermodynamic description of a wire is given in terms of only three coordinates 1. tension in the wire, ##\zeta## 2. length of the wire, ##L## 3. absolute...
  24. Z

    I Empirical temperature scales using different thermometers

    It took me a while to understand (I think) the concepts below. I have two questions. 1) What does "absolute" mean in the term "absolute temperature scale"? 2) What is the difference between the two constant-volume hydrogen gas thermometers (one at high pressure the other at low pressure)...
  25. Z

    Why does temperature fall in endothermic process in adiabatic system?

    In addition, "not all boundaries permit the transfer of energy even though there is a temperature difference between the system and its surroundings. Boundaries that do permit the transfer of energy as heat are called diathermal; those that do not are called adiabatic." If we have an...
  26. Z

    I Is it accurate to say work is motion against an opposing force?

    Is the following quote accurate: "The fundamental property in thermodynamics is work: work is done to achieve motion against an opposing force" Specifically, I am asking about the portion after the colon. I am a little confused by the notion of an opposing force. Let's say we are in outer...
  27. Z

    I Sign convention on work done to a closed system containing gas

    Here is the reasoning as it appears in the book. Consider the following setup Work (w) is a scalar quantity defined ##w=\vec{f}\cdot\vec{L}##. where ##\vec{f}## is the vector force and ##\vec{L}## is the vector length of path. If the force vector of magnitude ##\lVert \vec{f}\rVert## and...
  28. jeffinbath

    I Surely the 2nd Law of Thermodynamics is defied by gravity?

    As our sun and the other stars evolved from gravitationally led aggregations of hydrogen gas which permeated our early universe then that is an example of a high entropy system becoming a low entropy system and the so-called "arrow of time etc." was reversed?
  29. Juanda

    I Irreversible adiabatic processes & entropy change (clarification needed)

    Last month @Chestermiller opened the thread: Focus Problem for Entropy Change in Irreversible Adiabatic Process. I couldn't wrap my head around something apparently simple but the thread was not about that so I was instructed to open a new thread to discuss it separately and keep the original...
  30. Z

    What does it mean to specify the extensive state of an ideal gas?

    I was trying to solve the following problem at the end of chapter 1 of the book "Physical Chemistry", 4th Edition, by Silbey, Alberty, and Bawendy: Here is the information I collected about this topic in the chapter: 1) Intensive properties of a gas remain the same for any subsystem of a...
  31. Z

    How to understand this 3d surface of ##P,\bar{V}##, and ##T##?

    Here is the figure I would like to understand First of all, I don't see a specific surface. In the middle plot, I see what looks like the innards of a solid cube that has a large piece cut off. There is also an arrow annotated as "T=const". It is not clear what this arrow is pointing to. I...
  32. Z

    What does "limit of zero pressure" mean for ideal gas temperature?

    Here is the reasoning. We have three systems (A, B, and C) each consisting of a certain mass of a different fluid (ie, a gas or a compressible liquid). For the systems we are considering, we know from experiment that pressure and volume are independent thermodynamic variables and that the...
  33. immortalsameer13

    Can anyone recommend a good thermodynamics book that covers almost all concepts needed for bachelors study

    but at the same time give true essence of fundamental quantities i.e. what truely is heat? I have read couple of books where each book gives definition of quantities but not its essence.
  34. S

    I Entropy reversal in an infinite static universe?

    As far as I know, entropy could be reversed by the Poincaré recurrence theorem if it had a finite horizon given by some amount of vacuum energy causing an accelerating expansion. However, I found this lecture by Leonard Susskind () where he tells a way through which the vacuum could decay into...
  35. K

    Engineering Thermodynamics calculation: Flashing water at 75C

    Hello all, For a project I really need to know some number i can't seem to produce myself. we are flashing water @75 degrees Celsius, the water after flash-cooling is 67 degrees constant pressure is 0.27 bar (absolute) flow rate is 15000 KG/per hour. how much water is vaporized? Help is much...
  36. K

    Thermodynamics Energy when flashing water -- How much water will be vaporized?

    Hello all, For a project I really need to know some number i can't seem to produce myself. we are flashing water @75 degrees Celsius, the water after flash-cooling is 67 degrees constant pressure is 0.27 bar (absolute) flow rate is 15000 KG/per hour. how much water is vaporized? Help is much...
  37. C

    A Calculating the optical depth of an inhomogeous gas

    My question emerges from my desire to calculate the optical depth, which should be unitless, for an inhomgeneous cloud of radius ##r##. For a homogeneous medium, the optical depth can be defined in terms of the density of a cloud relative to the density of the condensed medium: $$\tau = \alpha...
  38. O

    I What role does Quantum Mechanics play in a internal combustion engine?

    Thermodynamics deal with quantum mechanics all the time, so I wondered what role it played in a internal combustion engine. Could we calculate it and how does it affect the engine's final output?
  39. E

    I Obtaining this form for molar energy under virial expansion (Callen)

    In his Chapter 13.3 (2nd edition), Callen gives the standard form for the virial expansion for the mechanical equation of state of a fluid as an exapnsion in powers of the molar volume ##v##: $$P = \frac{RT}{v}\left(1 + \frac{B(T)}{v} + \frac{C(T)}{v^2} + \dots \right) \equiv P_{ideal} +...
  40. E

    I Equilibrium constant change with stoichiometric doubling (Callen)?

    Callen asks us (with respect to an ideal gas) I had thought to proceed as follow. We have the definition for the singular reaction: $$\ln K_s(T) = - \sum_j \nu_j \phi_j(T).$$ Now a reaction which is the sum of this reaction with itself (doubled reaction) has ##\nu_j \to 2\nu_j## so that its...
  41. E

    I Is this an error in Callen?

    In Ch. 13.1 of the second edition, Callen defines a general ideal gas as follows: Of course, all of these can be proved as a theorem of statistical mechanics given a no-interaction assumption. At any rate, my claim is about Callen's claim that a single component ##j## of general ideal gas...
  42. E

    I How to see this form for the chemical potential of an ideal gas?

    In Chapter 13.2 of his text, Callen states that the chemical potential with respect to the ##j##th component of an ideal gas can be written as $$\mu_j = RT \left[\phi_j(T) + \ln P + \ln x_j \right].$$ He states this outright and doesn't prove it, and I am trying to do so now. Based on what has...
  43. JulesP

    Gibbs energy for Lithiation in Lithium batteries

    In writing up a paper on some research work on the effects of transients on Lithium Iron Phosphate batteries, I am laying out the thermodynamics and energetics for the reaction laid out below, but am having trouble finding the numbers for the reaction. Does anyone know the correct figures to...
  44. Lupin

    I How much energy (in Joules) is stored in a standard 12g CO2 cartridge?

    A standard 12 gram cartridge contains both liquid and gaseous CO2 at 850psi. Assuming we are venting to atmosphere at sea level, how much energy can be extracted from the cartridge? We know it will expand to 12 grams * 22.4 liters/ 1 mole (44grams) = 6.1 liters. But how much energy did...
  45. E

    Why is solid density used in this thermodynamics problem?

    Callen asks us the following question in his famous textbook: I have answered as follows: However, I get the wrong answer and, in fact, the correct answer obtains from using ##\Delta P = -\rho_s g h##; that is, using the solid density for the change in pressure. Now why on earth should this...
  46. E

    I Why is ##dQ = dH## still valid for chemical reaction (Callen)?

    Consider a system which is characterized by the extensive variables ##(U,V,N_1,...,N_m)##. For a quasistatic process which occurs in contact with some pressure reservoir and where the ##N_i## are constant, one has $$dU = TdS -PdV \implies TdS = dQ,$$ where the implication follows from the First...
  47. E

    I Why does Callen insist a process must be reversible here?

    In a discussion about the (change in the) Helmholtz potential being interpretable as the maximum available amount of work for a system in contact with a thermal reservoir (i.e. the free energy), Callen seems to insist this fact is true only for reversible processes. Why should this be? I...
  48. S

    Correct statement about thermodynamics process

    I know process B absorbs heat but I can't determine the heat of process A. In adiabatic process, Q = 0 but process A is not adiabatic. I only know both W and ΔU will be negative for process A but how to know Q? Thanks
  49. Demystifier

    A Thermodynamics/gravity/CFT correspondence

    Some evidence (Bekenstein, Hawking, Jacobson, Verlinde, ...) points to the idea that gravity is really a thermodynamic theory in disguise. Other evidence (Susskind, Maldacena, Witten, ...) points to the idea that gravity is dual to a lower dimensional conformal field theory (CFT). Are these two...
  50. Juanda

    Optimization of barrel length in pneumatic cannons

    I was checking bait cannons and potato guns on the internet because they are fun. Maybe one day I'll build my own. First of all, these cannons use multiple sources of energy (combustion using hair spray, dry ice, etc.). I'll just consider compressed air cannons because I think they are the most...