What is Thermodynamics: Definition and 1000 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. S

    I Internal energy of a comoving volume increasing as space expands?

    I was reading an article by Edward Harrison, which tackles the problems of conservation of energy at cosmological scales. At some part (point 2.4) he cites several article, including one by Rees and Gott, which he says indicates that the internal energy of a comoving volume (e.g. a cosmic...
  2. S

    I Energy from quantum systems in an expanding universe?

    I found a paper (https://arxiv.org/pdf/astro-ph/0411299.pdf) which talks about quantum systems emitting energy due to spacetime expansion. Is this true or only a hypothesis?
  3. S

    I Can trains use permanent magnets to be propelled?

    Can a train (e.g. like a maglev train) use a set of permanent magnets (not electromagnets) that somehow can be propelled and maintain at least a constant speed with them? Is this an example of such system...
  4. S

    I Is energy conserved during the formation of local systems?

    I found an old article (https://journals.aps.org/pr/abstract/10.1103/PhysRev.137.B1379) which talks about conservation of energy in an expanding space. Apparently, the author found that energy is conserved at local scales (like the motion of planets in our solar system) as one would expect, but...
  5. H

    I Exploring Work Done in Quasi-Static & Non Quasi-Static Expansion

    I'm wondering what's the difference between work done on quasi-static and non quasi-static expansion. In a quasi-static process, the gas inside the system must do a work to "extend". However, in a non quasi-static process, where the gas inside the system doesn't move fast enough to "push" the...
  6. casparov

    I Physics of paper absorbing Water -- Doesn't this decrease Entropy?

    Summary: doesn't this decrease entropy ? Cellulose is known for its hydrophilic quality, which can be explained from the polarity of its hydroxyl groups. We all know water can overcome the force of gravity through a piece of paper you put in the water. Correct me if I'm wrong but this is a...
  7. S

    Engineering Looking for calculations I could apply to a vacuum-forming machine

    So far I have determined the evacuation time, a basic heat transfer between the heating element and plastic sheet, and a hold down force of the forming bed.
  8. G

    B Does gravity defy the 2nd Law?

    Summary: Trying to understand the relationship between gravity, thermodynamics and entropy, thank you. Gravity can take a diffuse cloud of gas filling a given volume of space at equilibrium density and temperature, and turn it into a burning star surrounded by empty space. Does this mean that...
  9. TGV320

    Courses Question about studying Thermodynamics via the MIT online lectures

    Hello, Following previous advice for self studying, I am now looking at the physics curriculum of MIT through this link. http://catalog.mit.edu/subjects/8/ But at first I didn't find a course for thermodynamics, for the Phys I/II/III courses of the list don't provide it. Then I found that...
  10. L

    Finding both temperature and the amount of gas added

    The volume of the cylinder is ##V=\pi r^2 h=\frac{7\pi}{250}\ m^3## the number of moles is ##n=\frac{15}{16}\ mol## so from ##PV=nRT## we get ##P=\frac{nRT}{V}=25975.5\ Pa##. Now, for the second question, it should be an isochoric process so ##V_2=V_1## and ##P_2=P_1+0.8P_1=\frac{9}{5}P_1## and...
  11. Dario56

    I How Can Internal Energy of the Canonical Ensemble Change (Fluctuate)?

    Canonical ensemble is the statistical ensemble which is applicable for the closed system in contact with the reservoir at constant temperature ##T##. Canonical ensemble is characterized by the three fixed variables; number of particles ##N##, volume ##V## and temperature ##T##. What is said is...
  12. P

    Can someone give me hard thermodynamics problems?

    I finished first four chapters of Gaskell Thermodynamics of Materials and finished all exercises. Those 4 chapters are: first law, second law and statistical interpretation and introduction. Can someone give me fun problems to solve on these topics. I am really having fun solving those problems.
  13. Simobartz

    I Request for an example of minimum energy principle (thermodynamics)

    Summary: Request for an example of minimum energy principle usage The minimum energy principle states that, for a system at constant entropy, volume and other extensive quantities, the internal energy is minimized at equilibrium. Can you give me an example in which, using this principle, is it...
  14. mohamed_a

    I Problem regarding understanding entropy

    I was reading about thermodynamics postulates when i came over the differnetial fundamental equation: I understand that the second element is just pressure and last element is chemical energy, but he problem is i don't understand what is the use of entropy and how does it contribute to a...
  15. Hurcane

    Answer the question about time of cooling of a ball

    Hello, I'm not sure if this is the right place to post my question, however I still want to know. Recently, my teacher asked me the following question: "In which of the cases will the cooling time be the least: 1. the ball is suspended from the ceiling 2.the ball lies on a stand with a thermal...
  16. P

    Environmental Physics - Radiative forcing effect on greenhouse effect

    I think part (a) is simple enough. Here is what I have done. (a) ##G=\sigma T^{4}_{s} - OLR## $$ =\sigma (294)^{4} - 160 = 254 Wm^-{2} $$ Part (b) is where I am confused. I think I'm supposed to apply the second relevant equation, in order to get the change in average surface temperature due to...
  17. ContrapuntoBrowniano

    B Ideal gas formula not working?

    Hi! I wanted to do some basic calculations for temperature T on a water-filled pot. I noticed something strange on my calculations, and couldn’t figure out what was wrong... So here it is: The ideal gas formula: k=PV The actual formula Relates equally the product PV with the a constant...
  18. L

    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...
  19. Kolin101

    Academic First Law Of Thermodynamics Problem

    Hi there. I have a problem solving above problem. How can I move on with my solution? It seems to me that I have proper approach but I'm just stuck with the energy equation ;/ Part of solution below:
  20. S

    I How Does Electron Spin Affect the Partition Function in Saha's Equation?

    Hey, I have a question about proving Saha's equation for ionizing hydrogen atoms. The formula is \frac{P_{p}}{P_{H}} = \frac{k_{B} T}{P_{e}} \left(\frac{2\pi m_{e} k_{B}T}{h^2} \right)^{\frac{3}{2}}e^{\frac{-I}{k_{B} T}} with P_{p} pressure proton's, P_{H} pressure hydrogen atoms, m_{e}...
  21. M

    Partition Function for system with 3 energy levels

    I determined the partition function of the particle A, B and C. C should be the same as B. I then considered the situation, where all particles are in the system at the same time, and drew a diagram of all possible arrangements: The grey boxes are the different partitions, given that we...
  22. H

    A Is there a generalized second law of thermodynamics?

    Hi Pfs, There are different kinds of entropies. I discoved the free entropy. https://arxiv.org/pdf/math/0304341.pdf the second law says that the total entropy cannot decrease when time goes by. Is it always the same "time" for the different entropies? the author, Voiculescu, wrote articles...
  23. L

    Finding equilibrium temperature when there are phase changes

    If there weren't phase changes occurring I know that the temperature equilibrium would be ##T_e=\frac{m_{ice}c_{ice}T_{ice}+m_{w}c_{w}T_{w}}{m_{ice}c_{ice}+m_{w}c_{w}}##. Now, by repeating the reasoning to get the above formula (##\sum \Delta Q=0##) and adding the phase changes of the water...
  24. Dario56

    Derivation of McCabe - Thiele Method

    McCabe - Thiele method is used to find minimum number of separation stages or theoretical plates for a given efficiency of separation in distillation for two - component mixture if components have similar enthalpy of vaporization. If components have similar enthalpy of vaporization ,than on...
  25. jesmitter

    Thermodynamics Question About Steam

    How long does it take for 500 degree F - 1000 psi steam to move through 24" of 3/16 ID pipe and fill a 1 cubic inch volume cylinder to 1000 psi? Can it be modeled mathematically or with the help of Steam Tables?
  26. S

    I Magnetic fields are exceptions to the second law of thermodynamics?

    Einstein famously said “{Thermodynamics} is the only physical theory of universal content, which I am convinced, that within the framework of applicability of its basic concepts will never be overthrown.” I don't think any of us want to argue with Einstein, but it's worth noting the "within the...
  27. S

    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...
  28. samy4408

    Question about the rules of thermodynamics

    Hello , we learned in thermodynamics that to calculate ΔHr °(of the reaction ) using ΔHf °(standard heat of formation ), we have to respect that ΔHf °=ΔHr ° of a reaction forming 1 mol of compound from pure elements in their most stable form at standard state . the problem is when we want to...
  29. Galois_

    Thermodynamics - Latent Heat Problem (finding mass)

    Can someone walk me through this? Our teacher didn't bother to meet us synchronously ever since and I'm kinda stumped on solving this. The equation I used for this problem is: mi = [mw(cw)(ti-tf)]/[Lfi + (Tf - Ti)] mi = [190(1)(23-3)]/[79.6+(3+20)] = 37.04g mi = mass of ice mw = mass of...
  30. U

    Adiabatic expansion with temperature-dependent gamma

    The statement does not say whether the process is reversible or not, but I suppose the only way to solve the problem is by thinking it actually is. I tried using the formula for reversible adiabatic processes, i.e. PVγ = constant. First, I calculated the initial volume with the ideal gas law...
  31. G

    I Interpreting Thermal Power in Cylinder with Source & Sink

    I have a cylinder that is separated with an insulator. In the internal cylinder there is a thermal source, while outside the insulator we have a thermal sink. The power of the internal cylinder is positive, while of the external one in total is negative. How I should interpet the results. Like...
  32. Kamuna

    Thermodynamics Regenerative Rankine Cycle

    Summary:: regenerative rankine cycle Im a bit troubled by my home activity recently and maybe i could use some help this is the problem : In a steam power plant operating on regenerative Rankine cycle with one contact feedwater heater, steam enters the turbine at 8.0 MPa, 350 C and condensed...
  33. M

    I Partition function of mixture of two gases

    I have a question about statistical physics. Suppose we have a closed container with two compartments, each with volume V , in thermal contact with a heat bath at temperature T, and we discuss the problem from the perspective of a canonic ensemble. At a certain moment the separating wall is...
  34. C

    Entropy of spin-1/2 Paramagnetic gas

    As we know, dipole can be only arranged either parallel or anti-parallel with respect to applied magnetic field ## \vec{H} ## if we are to use quantum mechanical description, then parallel magnetic dipoles will have energy ## \mu H ## and anti-parallel magnetic dipoles have energy ## -\mu H##...
  35. Riverside

    A What Are the Mathematical Expressions of the First Law of Thermodynamics?

    About the mathematical expressions of the first law of thermodynamics
  36. guyvsdcsniper

    Evaluating a cycle [Thermodynamics]

    Since this is a cycle, there should leave the system unchanged, hence Q+W = 0. I wrote evaluated the heat and work done on/by the system at each cycle as shown in my work. The first question ask is work done at the fourth stage. Since this a cycle and again the system she remain unchanged...
  37. D

    B Infrared Detectors & The 2nd Law of Thermodynamics

    This started as an astrophotography question and morphed into a thermodynamics question & it was suggested to start a new thread in Thermodynamics. Essentially the question is how do I reconcile the behavior of particular infrared photodetectors with the 2nd Law of Thermodynamics? For example...
  38. Istiak

    I Book suggestions for classical thermodynamics

    I was looking for book on classical thermodynamics. I found lot of related posts in PSE but couldn't find a book which type I was expecting. I was searching for book which covers the whole thermodynamics (not QM but it's ok if there's some knowledge of Relativity), and I want some problems in...
  39. bob012345

    B Thermodynamics of Resistive Heating at Low Power

    Summary:: This is a question about resistive heating at low power in a thermally sealed chamber. Suppose one has a resistive wire inside a small very well insulated chamber that can stand very high temperatures such as 1500C. For applications such as a kiln, the heating element is powered at...
  40. D

    B HFC-134a Refrigerant & 2nd Law of Thermodynamics

    I am trying to reconcile HFC-134a refrigerant with the 2nd Law of Thermodynamics. I shouldn't be able to extract useful work from a single temperature reservoir. Suppose I use a refrigeration / heat pump cycle with HFC-134a as shown below. -Compressor adds 29 kJ/kg increasing refrigerant...
  41. M

    Engineering Thermodynamics: Determine pressure in the tank of a manometer

    I was watching a YT video getting prepared for class this coming semester, and in the video, this diagram of a manometer was drawn (see image at end of message). The professor stated that the pressure in the tank (Pt) is = to the pressure at point A. Following this, he said that technically...
  42. W

    Coping mechanisms for thermodynamics?

    Wasn’t sure whether I should post this here since it’s a more qualitative question, or under the Thermodynamics thread because that’s a more specific topic. For all practical purposes, the laws of thermodynamics are inviolable, and statistical mechanics puts them on an even firmer theoretical...
  43. Sai Maurice

    Populating a 1001x101 2D array in MATLAB

    The method I employed was based on a nested loop. I ran into two issues with this approach 1. The code took way too long to run, easily going for over 7 minutes. 2. In the end, it didn't even completely work, due to the "index exceeding the array length". This confuses me For the relevant...
  44. B

    Net efficiency of a cascaded Carnot Engine and Fridge

    Here is a diagram of my interpretation of the problem: Where I'm thinking that the engine originally takes heat from ##T_h## to ##T_l##, in which case ## \frac { Q_{h} } { T_{h} } = \frac { Q_{l} } { T_{l} } ## and ## W_{out} = Q_{in} - Q_{out} = Q_h \left( 1 - \frac {T_l} {T_h} \right) ##...
  45. E

    B Question about magnetizing and the First law of Thermodynamics

    I've been learning a lot about life from Internet searches and I do hope this isn't too basic of a question for you gurus. If I had two pieces of iron next to each other with a pea in-between and two pieces of cobalt with a pea in-between. Then I magnetized the four pieces of metal by brushing...
  46. D

    I Steam flow rate in 2-chamber steam engine system

    Our system of interest has a duct on the left and a piston chamber on the right that make the shape of the letter T rotated 90º clockwise. The smaller tube on the left is abbreviated as P1 has an unspecified length while the piston chamber is P2. The air in P2 heats up and expands while the...
  47. Yash Agrawal

    Thermodynamics of chemical reactions

    In chemical reactions generally ΔG < 0 , but if we were to consider a reversible path between pure reactants and products at 1 bar pressure , shouldn't the ΔG = 0 for every reaction ? and if it is due to non-pv work , I don't see any non pv work being done in reactions happing in a closed...
  48. cwill53

    I Change of Variables in Thermodynamics

    I have a question about changing variables in the context of thermodynamics, but I suppose this would extend to any set of variables that have defined and nonzero partial derivatives on a given set of points. First I should define the variables. ##T## is temperature, ##U## is internal energy...
  49. Thytanium

    I Are Newton's Laws of physics compatible with thermodynamics?

    Good day friends. I want to know and ask you if Newton's laws are incompatible with thermodynamics.
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