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. Selveste

    Finding Pressure, Temperature, and Chemical Potential for a Non-Ideal Gas System

    Homework Statement A generalized TdS-equation for systems of several types of "work-parts" and varying number of particles in multiple components, is given by dU = TdS + \sum_{i}y_idX_i+\sum_{\alpha =1}^{c}\mu_\alpha dN_{\alpha} Thus, its natural to regard the internal energy U (an...
  2. D

    Chemical thermodynamics, entropy, Maxwell relation and Z

    Homework Statement A gas obeys the equation of statez=1/(1-b(molar density)) What is the molar entropy change of expanding this gas from a volume of 1 dm3 to 2 dm3 at a temperature of 300 K, given b = 0.2 dm3? Calculate your answer to three significant figures and select one answer from the...
  3. andrewkirk

    Insights Partial Differentiation Without Tears - Comments

    andrewkirk submitted a new PF Insights post Partial Differentiation Without Tears Continue reading the Original PF Insights Post.
  4. Konte

    I Quantum thermodynamics of single particle

    Hello everybody, I have two questions: 1) Is it possible to define a temperature for single particle (or atom or molecule)? If so, how? 2) How to model with quantum Hamiltonian an exchange of energy between a single atom (or molecule) and a reservoir at given temperature ##T## ? Thank you...
  5. SpinzTronics

    Thermodynamics - expansion, compression, work

    Hi everyone! I am confusing myself with this topic and I would appreciate some insight into this. You see, one takes the area of a PV graph to obtain the work done on the system (for compression) or by the system (for expansion). However, I am learning that in the irreversible path, compression...
  6. S

    2nd law of thermodynamics question

    The reaction CO2 + 4 H2 <==> CH4 + 2 H2O (liq) at 25oC is downhill with a gibbs energy of -31 kcal/mol. It has a negative entropy of -98 cal/K. Thus an isolated system of the two starting gases should go to equilibrium on the basis of the Gibbs energy value, but the process would then...
  7. N

    What is the Relationship Between Gas Ionisation and Temperature?

    Homework Statement When a gas is enclosed in an impermeable box and heated to a high temperature T, some of the neutral atoms lose an electron and become ions. If the number density of neutral atoms, ions and electrons is Na , N i and N e , respectively, these can be related to the average...
  8. P

    Amateur physics here, how is entropy linked to the universe?

    I learned about entropy is chemistry, can someone please explain how this term is used in physics? Thanks.
  9. dUDEonAfORUM

    Thermodynamic problem and formula homework help

    An ideal gas at initial state has temperature 300 K has been compressed under constant pressure of 30 Pa from volume 3 cubic meters to 1.8 cubic meters. In the process 75 J of heat was lost. A. Find the change in internal energy B. Find the final temperature I tried two methods in A and they...
  10. arpon

    How to Derive the Equation for Internal Energy in Thermodynamics Homework?

    Homework Statement Derive the equation ##U=-T(\frac{\partial A}{\partial T})_V## where ##U## is the internal energy, ##T## is the temperature, ##A## is the Helmholtz function. Reference: Heat and Thermodynamics, Zemansky, Dittman, Page 272, Problem 10.4 (a) Homework Equations ##dA=-PdV-SdT##...
  11. Q

    Fluid Boundary layer in presence of a postive heat gradient

    I was wondering how a boundary layer would be dissipative of momentum if it was under the influence of a positive heat gradient. I understand that the reason that we don't see the boundary pressure equal the stagnation pressure is that the boundary is dissipative (so excess pressure above...
  12. Z

    Classical How good is this Thermo textbook?

    Thermodynamics (Yunus Cengel Michael Boles , 8) I'm taking Thermodynamics right now at my community college and if you saw my last post about my physics teacher, you know I have the right to be paranoid about not learning enough in my classes. I've always heard Thermo for mechanical engineers...
  13. M

    Thermodynamics College Project

    Hi there, After spending a lot of time reading topics on the forum, and knowing that I have a TIPE( Project in French Prep School Prior to entering engineering big schools) to do for the year (I am in 2nd year of scientific preparatory school ( So i am 19 )) I decided to launch a project to...
  14. MikeW

    Thought Experiment on the Second Law of Thermodynamics

    Hi, I have a thought experiment which seems inconsistent with the 2nd Law of Thermodynamics, so there is probably a flaw in the idea somewhere. Imagine a single molecule of a heavy gas (such as SF6) in a pipe 2.5 metres high and 100mm diametre. The pipe is upright and under the normal...
  15. R

    Compressor Problem in thermodynamics

    Hello, I am working on the following problem: Homework Statement -------------------------------------------------------------------------------------- During the modifications in the process you are working on, your direct boss is interest in replacing a few equipment for new ones in order to...
  16. L

    Interested in thermodinamics, quantics and astrophisics

    My name is Liviu Marinica, I was born in Romania, and I am an 48 yo electrical engineer. My background in engineering is related to office work (design) but also field service work for electrical power equipments such as medium and low voltage switchboards, protection relays (called IED, or RTU...
  17. Elvis 123456789

    Change in entropy of an ideal gas during thermodynamic cycle

    Homework Statement An ideal gas with adiabatic index γ is taken around a complete thermodynamic cycle consisting of three steps. Starting at point A, the pressure is increased at constant volume V1 from P1 to P2 at point B. From point B to point C, the gas is allowed to expand adiabatically...
  18. S

    Thermodynamics Energy balance equation for Non - Steady Flow

    Hi, I am currently studying Thermodynamics and stumbled upon this equation and is slightly confused as to how this works. Hopefully someone can help me with the understanding. According to this text here, if I am not wrong e can be h + ke + pe or u + ke + pe depending on where i am looking...
  19. physicsBabyMetal

    What's the relation with Gravity & Laws of Thermodynamics

    Here's a thought from other thread A reply So what's the relation between gravity and the laws of thermodynamic, or should it be conservation of energy?
  20. TheDemx27

    How to Calculate Heat Current in a Spherical Shell?

    Homework Statement A spherical shell has inner and outer radii r_a and r_b, respectively, and the temperatures at the inner and outer surfaces are T_a and T_b. The thermal conductivity of he shell material is k. Derive an equation for the total heat current thought the shell in the steady...
  21. Pao44445

    How Fast Does Temperature Rise in an Unventilated Silicon Circuit?

    Homework Statement A silicon electric circuit is 23 mg, when electricity flows through the circuit rising the energy by 7.4 mW but this circuit wasn't design for heat ventilation. Find the rate of how much the temperature is rising per second ( ΔT/Δt ) The specific heat of silicon is 705...
  22. J

    Heat capacity under constant pressure or volume question

    HOMEWORK POSTED IN WRONG FORUM, SO NO TEMPLATE I have encountered a problem at the university in which there is a thermally isolated container of constant volume in which the number of particles and temperature change with time(the temperature increases). The change in particle number ensures...
  23. L

    How to derive this heat input equation?

    There's one equation that I've seen being used already, which by itself is quite simple, but I can't understand where it comes from. The context is as follows: suppose we have one heat engine operating between systems A and B whose temperatures are T_A>T_B. Let's suppose further that the...
  24. F

    Confusions about thermodynamics

    1. Can I say Carnot efficiency of a heat engine is always smaller than 100 because the temperature of cold reservoir is always greater than 0 Kelvin? 2. Is the following analogy correct to describe the relation between temperature and heat energy? "Heat energy affects internal energy which...
  25. Z

    I How do you find Z when the temperature line ends on the compressibility chart?

    How do you find a value for Z using the compressibility chart when the temperature line you're trying to use ends? For example, if you look at the compressibility chart and try to find a value for z with P_r = .75 and T_r = .96, you will notice that the line for T_r = .95 ends well before the...
  26. Z

    Why isn't the temperature of this vapor T_sat?

    A rigid tank with a volume of 2.00m3 contains 5.77 kg of saturated liquid-vapor mixture of water at 75 deg C. Now the water is slowly heated. Determine the temperature at which the liquid in the tank is completely vaporized. Why isn't the temperature just 75C? If it is already a mixture in...
  27. S

    Energy change of reservoir in reversible weight process

    In what follows I refer to the ideas of "Thermodynamic: Foundations and Applications" by Gyftoploulos and Beretta. The abbreviated form of my question is: In a reversible weight process, Ω1R-Ω2R = E1 - E2 (see eqn. 6.18, p. 99) is transferred out of the composite of a system A and a reservoir R...
  28. Z

    Why can we assume the temperature of a fluid is T_sat?

    For example, in this question.. A 11 L rigid container contains 10-kg of R134a at 100kPa. Determine the temperature and total enthalpy in the container. Why can we just assume that the temperature we're looking for is T_sat, how do we know this isn't a compressed liquid? How do we know it...
  29. Elvis 123456789

    Adiabatic expansion of an ideal gas

    Homework Statement An ideal monatomic gas has initial pressure Po and occupies initial volume Vo. The gas undergoes an adiabatic expansion in which the volume is doubled. Calculate in terms of Po and Vo a) the final pressure of the gas b) the change in its enthalpy during the...
  30. S

    1st law, 2nd law, entropy by Gyftopoulos / Beretta is confusing

    I'm reading Thermodynamics: Foundations and Applications by Gyftoploulos and Beretta, because the authors claim to give a presentation of classical thermodynamics without "... the lack of logical consistency and completeness in the many presentations of the foundations of thermodynamics" [from...
  31. T

    Which Thermodynamics Demo Best Illustrates the Laws of Energy?

    So I need to give an exciting thermodynamics demo based on one of the first two laws. I have found it difficult to either make it exciting enough or to make it apply to thermodynamics enough. I have a few that I have come up with but I don't think any really apply as well as I want. 1)Can...
  32. M

    Thermodynamics problem 1st law

    Homework Statement Air flows steadily into a well isnulated piping junction through the two pipes and is heated by an electric resistor at uknown rate befoe exiting through the pipe. Pressure renaubs approcimetaly constant p=0.1 MPa, first inlet: volumetric flow rate = 10m^3/s, t1= 20 C, 2nd...
  33. H

    Non-Linear optics vs The 2nd Law of Thermodynamics

    Hi, rank newbie here, with my first post. This one is something I figure every first year student comes up with at some point, but I don't know enough keywords to Search for an answer. (I'm not a student except in the category "of life": this isn't assigned homework) I figger, using a bit of...
  34. Jefffff

    Thermodynamics of an Arctic greenhouse?

    For a business project, I'm looking into the viability of a greenhouse situated in Canada's far northern town of Iqaluit. The problem is how to mathematically simulate the internal air temperature of the greenhouse. What I already have are detailed 3D renderings of the greenhouse as well as all...
  35. Monsterboy

    Is the second law of thermodynamics a law or a tautology?

    I was reading an answer on Quora written by Richard Muller ,a retired professor from Berkeley https://www.quora.com/Does-Richard-Mullers-new-time-theory-account-for-the-second-law-of-thermodynamics-or-any-of-times-arrows/answer/Richard-Muller-3?srid=E7fv What are your views ? I am from...
  36. P

    What is the maximum temperature of a dual cycle with given parameters?

    Homework Statement Find the maximum temperature in deg C of the dual cycle with initial temperature of 30 deg c, compression ratio of 6, cut off ratio of 2.5 and the heat addition at constant volume process of 600 kj/kg. y= 1.4 cp= 1.005 kj/kgk cv=0.718 kj/kgk rv=6 rc=2.5 Qadded @ Cv = 600kj/kg...
  37. TheAnt

    Thermodynamics : https://www.youtube.com/watch?v=uc9P5yb3Xtc

    Hi I had a question about this video. Indeed if I understand the video correctly it states that energy is linked to information. But how does that work indeed knowing that energy is constant, that more entropy = less information and that entropy increases. It seems that the universe will end...
  38. F

    I Are There Always Conditions for Writing Q=CΔT in Heat Transfer Processes?

    When dealing with heat transfer, there are cases where Q can be expressed by C*ΔT, for some proportionality constant C. However, in isothermal processes for example, this formula would lead to a mistake, for any value of C (because it would imply Q=0, which is not true generally speaking). What...
  39. DrClaude

    Phase transition in rotating balls

    A very neat video showing a phase transition in rotating balls in a cup. Serves as a good analogy to other phase transions.
  40. E

    Book of T-S diagrams, or the like

    Hello - I just starting out in chemical engineering. I hold a batchelor's degree in Chemistry, and am making a transition to ChemE. This isn't for any class, just in general for reference, does anyone know of a good book that is primarily just thermodynamic charts, like T-S diagrams? I have...
  41. D

    Thermodynamics and Carnot engines - university exam question

    Homework Statement A block of radioactive material is ti be used as a power source for a deep space probe which may be treated ideally as a single Carnot engine. Radioactive decay generates heat in the block at a rate Pin = dQin/dt and heat is extracted from the block to operate the probe at a...
  42. Titan97

    Specific heat for a triatomic gas

    Homework Statement Using equipartition law, find specific heat of gas containing triatomic linear molecules. Will the result be different if the molecule was non- linear? In what way? Homework Equations According to equipartion theorem, each degree of freedom gets (1/2)kT kinetic energy and...
  43. R

    Thermodynamics rankine cycle problem

    1. Steam is the working in an ideal rankine cycle with super heating . Super heated vapor (state 1) enters the turbine at a temperature of 440 °C. Saturated vapor(state 2) exits the turbine at a pressure of 3.0 bar.2. a) Sketch T-S diagram. b)Determine the thermal efficiency of the ideal...
  44. T

    Quantification of Entropy and the 2nd Law of Thermodynamics

    All of my information comes from my current chemistry class, I just want to know where I either may have misread, misinterpreted, or was mistold information. With the 2nd Law of Thermodynamics we can say $$[1]\space\space \Delta{S}_{universe} = \Delta{S}_{surroundings} + \Delta{S}_{system} >...
  45. B

    B Can the Bohmian Wave Function Influence Thermodynamic Trajectories?

    I know thermodynamics are the macroscopic coarse graining of microscopic degrees of freedom (like temperature and Brownian motion). But is there a case where let's say the bohmian wave function can create trajectories of particles that can control the macroscopic thermodynamics or has...
  46. T

    Why the temperature remains constant at the boiling point?

    Why all liquids vaporize on boiling point instead of the temperature gradually increasing along with vapor pressure and more liquid atoms evaporating? Does it have anything to do with formation of vapor bubbles?
  47. V

    Thermodynamics -- Relation between ##dT## and ##dV##

    Homework Statement Homework EquationsThe Attempt at a Solution If I consider a specific case of adiabatic process , then ##dQ = 0 ## and ##dU = -PdV ## If we differentiate with respect to T on both sides , ##\frac{dU}{dT} = -P\frac{dV}{dT}## . Now , the closest I see is option B) , but...
  48. M

    How Do Entropy and Mass Relate in Black Hole Thermodynamics?

    Homework Statement I would very much like getting some help with my problem regarding the equations in some black hole thermodynamics. "Using the expression for the Schwarzschild radius, the entropy of a black hole of event-horizon area A=πR^2 can be written in terms of its mass using Eq. (1)...
  49. Nantes

    Thermodynamic cost of information processing (or lack thereof)

    Say you wanted to heat up your room. You could choose between an electric heater that outputs 500W or a PC that draws 500W. In both cases, the amount your room would heat up by would be the same, but the second case is much more advantageous because the computer can process information before...
  50. T

    Calculating combustion temperature of mixture

    Hey guys, I'm trying to write a small article that very simply explains some of the math involved with a rocket engine. I'm not looking for a very accurate answer so I tried the following method 1) Stoichiometry on the fuel which was sugar and saltpeter and their respective enthalpies of...
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