Thermodynamics Definition and 1000 Threads

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. H

    Thermodynamics pure substances problem

    Homework Statement Hellooo, so this is the question that i have: A 0.5-m3 rigid tank initially contained a saturated liquid-vapor mixture of water at 140 °C is now heated until the mixture reaches the critical state. Determine the mass and the volume of liquid before the heating process...
  2. zawy

    Is the Moon responsible for reducing Earth's entropy and making life possible?

    Spontaneous negative entropy reactions can occur when the internal energy decrease is greater than the negative dS*T. dG=dU-dST is spontaneous if dG is negative. The moon is receiving at least 1E8 J/s from the loss of rotational energy from the Earth's water and air. A lot more rotational...
  3. Titan97

    Thermodynamics problem involving piston and spring

    Homework Statement [/B] Homework Equations $$W=P\Delta V$$ $$\Delta U=nC_v\Delta T$$ The Attempt at a Solution . [/B] The gas is slowly heated. The temperature increases and the pressure increases as well. But since volume increases, the increases in pressure is nullified. The process is...
  4. Marcin H

    Heat and Internal Energy - Thermodynamics

    Homework Statement 10g of water at 0˚C added to 100g water at 50˚C Homework Equations Qhot+Qcold=0 Q=mcΔT Q=mL Σmc(Tf-Ti)=0 The Attempt at a Solution So I understand this problem, but I'm not sure when I am supposed to use Q=mL, L being the latency, I think. So with the problem mentioned you...
  5. K

    Thermodynamics problem. Have I answered this correctly?

    Homework Statement Two rigid containers, A and B, contain the same type of ideal gas and are connected by a thin tube which has been fitted with a valve. The initial pressures of the gases in A and B are P_1 and P_2, respectively, whilst the initial temperatures are T_1 and T_2, respectively...
  6. B

    What is the final temperature of the mixture?

    Homework Statement In an experiment, 1.1kg of aluminium is heated to 92 degrees Celsius it is then dropped into 0.5kg of water at 12 degrees celsius. Find the final temperature of the mixture. (Cw= 4200JKg-1Celsius-1) (Cal= 880JKg-1Celsius-1) Homework Equations Qal = Qw The Attempt at a...
  7. K

    Physical Chemistry Homework: Equilibrium Constant and Gas Properties

    Homework Statement I have the following task: A chemical reaction 2 A(g) <-> B(g) + C(g) has an equilibrium constant defined by: ln=0.8+ 1050/T−1,3.105/T² a) What is K at 400K? Calculate ΔrG0 In a volume of 5L you get 2 moles of A and 0.5 moles of B. Reaction still proceeds at 400K. Consider...
  8. S

    Help with Thermodynamics and Gas Law

    THE PROBLEM: A steam engine's boiler completely converts 2638 g of water at 83.7 °C to steam at 195.4 °C. The steam, at a constant pressure of 3.28 Pa, expands by pushing a piston of radius 9.4 cm a distance of 8.3 cm. What is the change in internal energy of the water-steam system? MY WORK...
  9. Y

    Thermodynamics: Relationship between deltaX, partialX, dx

    Homework Statement I am trying to understand the the following derivation: Cv = (qv/ΔT) = (ΔU/ΔT) \\ Cv = (∂U/∂T)v \\ dU = CvdT The Attempt at a Solution [/B] So here is what I understand so far. I understand that heat transfer q and temperature T are related by a direct...
  10. S

    Maximum work obtained by mixing 2 gases

    Homework Statement 2 boxes containing the same number of moles of 2 ideal identical gases with the same adiabatic index (this is given as gamma), at the same initial temperature Ti but with different volumes, V1 and V2 are brought together. Find the maximum mechanical work that can be obtained...
  11. UchihaClan13

    Sign Convention for Work (In Thermodynamics)

    Okay so after reading various books on sign conventions for work I am told by my teachers that in chemistry,work done on the system is positive while work done by the system is negative while in physics it's the exact opposite I only use the former convention And modify the first law of...
  12. leafjerky

    Water, piston-cylinder problem [Thermodynamics]

    Homework Statement Okay, so these are usually pretty easy for me to understand, but this one doesn't make sense. 10 kg of water in a piston cylinder arrangement exists as saturated liquid/vapor at 100 kPa, with a quality of 50%. It is now heated so the volume triples. The mass of the piston is...
  13. Titan97

    Thermodynamics problem involving adiabatic vessels

    Homework Statement Two adiabatic vessels containing ##n## moles of mono atomic and diatomic gas respectively are connected by a rod of length ##l##, cross sectional area ##A## and thermal conductivity ##k##. The surface of the rod is insulated. The initial temperatures of the vessels are...
  14. T

    Thermodynamics: ΔE vs ΔU - Uncover the Difference

    My question is what is the difference between ΔE and ΔU. Because I see both equations 2 and 3 interchangeably . But then I see equation 1. So there has to be a difference between them since they are using both symbols in one equation. I thought U was internal energy while E was total energy...
  15. Abtinnn

    Is temperature directly linked to movement?

    Hey guys, I have been wondering about this for a long time, and I can't seem to reach a solid conclusion. If temperature of an object is related to the movement of its atoms, then is it true to say that a moving object have a higher temperature?
  16. A

    How can the simplification of equation I.4 using equation I.5 be justified?

    I was studying zeroth law from MIT Courseware (http://ocw.mit.edu/courses/physics/8-333-statistical-mechanics-i-statistical-mechanics-of-particles-fall-2013/lecture-notes/MIT8_333F13_Lec1.pdf). On page 2, it is mentioned that equation I.4 can be simplified using equation I.5 by cancelling the...
  17. Cora

    Ideal Gas Expansion State Properties & Exergy Balance

    Homework Statement Two well-insulated rigid tanks of equal volume, tank A and tank B, are connected via a valve. Tank A is initially empty. Tank B has 2 kg of Argon at 350 K and 5000 kPa. The valve is opened and the Argon fills both tanks. State 2 is the final equilibrium state. The temperature...
  18. mfig

    I Why do we see the claim that an isentropic process is adiabatic and reversible?

    Why do we always see the claim that an isentropic process for a system is adiabatic and reversible? The change in entropy for a process is the sum of the entropy transfer accompanying heat and the entropy production. The entropy production term is always at least zero, and the transfer term...
  19. A

    Why define entropy with heat instead of work?

    From what I understand, in the Carnot cycle summing qi/Ti for each step results in zero, thus indicating a new state function, entropy = qrev/T. But since dE = 0 = q+w, then q = -w, and looking at the equations derived from the cycle summing wi/Ti for each step should also result in zero. So why...
  20. kini.Amith

    Basic problem in equilibrium thermodynamics

    I was reading Thermodynamics by Herbert Callen. In the first chapter he makes the following statement. 'The basic problem of thermodynamics is the determination of the equilibrium state that eventually results after the removal of internal constraints in closed composite system.' Then he...
  21. O

    First Law of Thermodynamics and Melting-Ice Scenario?

    In order to explain the change in energy of an ice cube removed from a refrigerator and placed on the kitchen counter, I consider it as a closed system (can exchange only energy but not matter). For the first law of thermodynamics, ∆U = Q+W. I'm pretty sure that the sign of Q is positive due to...
  22. M

    Low-pressure turbine system heat xchanger?

    Hi Guys, A question that I've been mulling in my mind over the last few days, is it is practically possible to make a low pressure 'turbine' system at atmospheric pressures? I was looking at a low-pressure stirling engine, and wondering if the same thermodynamic principles would equally be...
  23. Ryaners

    Calculating entropy change associated with change in temperature

    Hi folks, This is a question about how to calculate entropy change when there is a temperature change involved. I got the correct answer to this, but I don't actually understand why it's correct..! Any help is much appreciated. Homework Statement One mole of liquid bromine is heated from 30...
  24. B

    Is "energetics" the same as "thermodynamics"?

    If so, why do people use the word "energetics"?
  25. KMote

    Does Maxwell's Demon violate the 2nd Law of Thermodynamics

    I'm a newbie (obviously), but I just read this recent paper describing an "experimental realization of an autonomous Maxwell’s demon" (along with this review). I think I understand the general concept of Maxwell's thought experiment well enough (from a layman's perspective), but I'm having...
  26. G

    Expansion of the Universe and Thermodynamics

    Hello, I have a very basic question about the expansion of the Universe and it could be that I'm being very stupid here: if the universe is expanding into the empty surroundings as the red shift evidence seems to demonstrate, then surely the universe must be doing work on the surroundings like...
  27. M

    Specific Heat Capacity for Gas

    So I have a question regarding the specific heat capacities in thermodynamics. In general the specific heat capacities for a gas (or gas mixture in thermo-chemical equilibrium) can be expressed as, ## c_p = \left(\frac{\partial h}{\partial T}\right)_p \qquad \text{and} \qquad c_v=...
  28. D

    Solving Gas Chamber Problem: Pressure Equality in 3 Compartments

    Homework Statement Consider a rectangular isolated(non-conducting) chamber as shown below. The chamber is divided into three compartments. The wall separating A and B has negligible mass, no friction and is conducting, while the wall separating B and C has negligible mass and friction and is...
  29. DanielSauza

    Nozzle/Diffuser equation for compressible flow

    I was reading a bit about comrpessible flow and I came upon a problem, there's a diffuser which has air at Ma=0.9 at its inlet and the air comes out at 0.65, how should I go about finding the ratio of the inlet and outlet areas? I know It's related to this equation but I'm unsure about how...
  30. E

    Torque of rotating coaxial cylinders with gas between them.

    I was going through a worked example in book "Concepts in Thermal Physics" by S.J. Blundell and K.M.Blundell. The example talks about measuring viscosity of a gas between two coaxial cylinders. Homework Statement Two vertical coaxial cylinders. Outer cylinders is rotated by a motor at constant...
  31. J

    What is the Zeroth Law of Thermodynamics and why is it causing confusion?

    This is not a homework problem. I want to relay a statement made by my professor. From his online script: "0th law of thermodynamics: If two subsystems I,II are separately in thermal contact with a third system, III, then they are in thermal equilibrium with each other." He stated this in...
  32. S

    How to calculate amount of vapor given q(t) and p(t)?

    Hi everybody, I am trying to build a small model which basically should be able output "mass flow of water vapor as a function of time" given following inputs: - initial mass liquid water m_l_0 [kg] - initial temperature of liquid water T_l_0 [°C] - initial pressure p_0 [Pa] - heat added as...
  33. S

    Understanding the Exit Pressure of Nozzles in Thermodynamics

    Hi There, Im studying thermodynamics at the moment and there's one statement about nozzles that I just haven't been able to understand. In my mind when a fluid exits a nozzle it would have a higher pressure than the inlet. Could someone please explain in what sense the pressure of a fluid drops...
  34. T

    How to find the specific heat capacity of a mixture?

    Homework Statement For my physics IA, I am finding the specific heat capacity of water-solute mixtures and finding how the specific heat differs from that of just water alone. I have the mass of the mixture, for example baking soda and water was 914.75g and changed 175.8 degrees Fahrenheit in...
  35. K

    Thermodynamics, saturated Pressure and temperature

    I wonder why we can find temperature (or pressure )when the other property value is given.Lets say we have a rigid tank, which contains 50Kg of water at 90 degree celsius. If we look up the thermodynamics table, we can find the saturation pressure 70.14 kpa and definite liquid and gas specific...
  36. Luis Obis

    Isobaric process for a Van der Waals gas

    Homework Statement [/B] You are asked to calculate changes in internal energy, entropy, heat transferred and work done for each of the following process. Also you are asked to calculate "the latent heat for the isotherm in the figure". We know the a and b parameters which characterize the VdW...
  37. B

    (Thermodynamics) A tank with water & air heated

    Homework Statement For a rigid, impervious, closed tank - The volume of tank is filled with 70% water and the rest is with air- The initial temperature of the tank is 20 °C, and the absolute pressure is 1 bar. - What would be the final pressure if we raise the temperature to 200 °C? Homework...
  38. S

    Converting PV Diagrams to TS Diagrams in Thermodynamics

    Hello, Can u please explain how to convert a PV diagram to a TS diagram in thermodynamics. Thanks in advance
  39. S

    More ebooks about Maxwell relations of Thermodynamics

    I'm learning about Maxwell relations of Thermodynamics, but it's difficult for me to find more books about this in Vietnamese. So, I want to ask you about some english ebook about this. Thanks a lot!
  40. P

    Thermodynamics Control Volume evaluation 2 inlet

    Figure P6.95 provides steady-state test data for a control volume in which two entering streams of air mix to form a single exiting stream. Stray heat transfer and kinetic and potential energy effects are negligible. A hard-to-read photocopy of the data sheet indicates that the pressure of the...
  41. D

    Why is delta-H equal to q at constant pressure?

    Homework Statement In my lecture notes(beginner thermodnyamics), we just got introduced to the first law(DeltaU=q+w) and two scenarios. One at constant volume which yields the equation Delta U = qv. I understand that The second scenario is at Constant pressure and it says that At constant...
  42. Mbywater94

    Understanding the use of a figure in thermodynamics.

    I came across an equation used in one of the forums from a few years ago. Found here: https://www.physicsforums.com/threads/calculate-how-long-it-will-take-for-the-ice-to-melt.531908/ I am researching a similar topic into melting ice and using it as a cooling solution. However when i came...
  43. D

    Understanding Work and Heat Transfer in Thermodynamics

    Homework Statement My lecture notes says that Work is the transfer of energy by means of a force acting on an object/body. What about heat energy? Does work also need to be done to transfer heat energy from hot object to cold object? Say if i drop a hot metal into room temp water. The metal...
  44. N

    Thermodynamics -- hydrostatics question

    Good afternoon. You are a student of the career of physical I am 'm like someone aids with the second section (II) the following problem because I do not understand much. Thank you very much. Problem: Considering that the effects of pressure variation with height are due only factor hydrostatic...
  45. B

    Constant Volume Calorimetry - Why does (ΔnRT)=(Δn)RT

    When doing constant volume calorimetry, the enthalpy can be calculated as follows: ΔH = ΔU + Δ(PV) ΔH = w + q + Δ(PV) ΔH = PΔV + q + Δ(PV) and at constant volume: ΔH = q + VΔP which I've then see people rewrite using the ideal gas law as follows: ΔH = q + (Δn)RT where Δn is the change in...
  46. B

    Thermodynamics -- Internal Energy

    I've read back and forth in my chapter and tried consulting with my forumla sheet, but I cannot seem to find the correct formula. I bet I am looking at this question wrong, but I am fairly sure I need to use the -100 kJ for something to find the final volume and pressure , along with the given...
  47. A

    Calculating entropy generation of a process

    Lets say we have T1. From a reservoir 4000K, Q is added and that makes the temperature T2. How do we calculate the entropy generation in a process like that? Isn't it Sgen=S2 - S1 - (Q/T) But which temperature we will use in the (Q/T)? T1, T2 or 4000K?
  48. Ravyan Asro

    Does temperature in special relativity depend on the frame of observation?

    if two bodies are in thermal equilibrium in one frame, will they be in thermal equilibrium in all frames? also, does the temperature of a body depend on the frame from which it is observed?
  49. A

    Thermodynamics (work done by unrestrained gas expansion)

    https://www.physicsforums.com/attachment.php?attachmentid=20388&stc=1&d=1252066499When the partition removed, gas flows into the vacuum until all system has a uniform pressure. Now, is it possible to calculate the work? Let's say gas is not an ideal gas.(Freon 12) We know the volumes of both...
  50. A

    Thermodynamics (Entropy Generation and Heat Engine)

    Homework Statement A hot gas stream at 600K and 200 kPa is cooled at constant pressure to 300K in a pipe by direct thermal contact with the atmosphere. The mass flow rate of the stream is 0,1 kg/s and the atmospheric temperature and pressure are 300K and 100 kPa. Modeling the gas as an ideal...
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