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. Uthpala Kaushalya

    Thermodynamic Equilibrium

    Homework Statement Consider a rigid piston cylinder arrangement. Assume that the cylinder and the piston are covered by a perfectly insulating material and the piston cylinder interface is very smooth. Two types of ideal gases are separated in the cylinder by the piston. The number of gas...
  2. K

    A What if black holes can violate second law of thermodynamics

    GUT's violate baryon number b/c baryon conservation is an emergent phenomenon second law of thermodynamics clearly applies to macroscopic systems, and are the result of the many ways in which atoms of macroscopic systems can be arranged. what if second law of thermodynamics though is just...
  3. Karan Punjabi

    Understanding Chemical Thermodynamics: Exploring the Concept of State Functions

    Guys I am getting confused that what is state function? People say if state changes then state function also changes. But my view is if that variable changes then only state changes and its not necessary when a state change will always lead to change of every state function.
  4. Dr. Who

    I Relation between 'P' and 'V' for an Adiabatic process

    Hi All, I have a little query concerning the derivation of PV γ = constant. In my textbook of Physics, first they give the equation for adiabatic process using the first law of Thermodynamics, as; dEint = W → (1) where, ΔEint ⇒ change in internal energy and W ⇒ workdone Then, they used...
  5. Schwarzschild90

    Canonical partition function for N ideal gasses

    Homework Statement Exercise 4 in the upload titled Dok1.pdf. Write down an expression for the canonical partition function for N ideal Na2 gas molecules, when the rotational contribution is treated classically, and all inner degrees of freedom are treated quantum mechanically. Use this and...
  6. Einstein's Cat

    I Does Black Hole Evaporation Violate the Second Law of Thermodynamics?

    Hawking showed that black holes dissipate energy when virtual particles are "emitted" by black holes and therefore black holes evaporate. However it seems to me that a shrinking black hole means a decrease in entropy and thus a violation of the second law of thermodynamics; is this the case?
  7. C

    Another "Partial Derivatives in Thermodynamics" Question

    Hi all, It seems I haven't completely grasped the use of Partial Derivatives in general; I have seen many discussions here dealing broadly with the same topic, but can't find the answer to my doubt. So, any help would be most welcome: In Pathria's book (3rd ed.), equation (1.3.11) says: P =...
  8. Ben S

    Thermodynamics - property relationship of 2 systems

    Homework Statement A pure substance is placed into two containers of the same volume. Container 1 has twice the mass of pure substance of Container 2. After the containers are shut and both reach thermal equilibrium with the surroundings, what do we know about: a) the pressure of Container 1...
  9. Tulio Cesar

    How Do Carnot's Efficiency Formulas for Heat Engines Align?

    My question is: according to Carnot cycle, the maximum efficiency of a heat engine is given by 1 - T2/T1, where T2 is the temperature of the cold source and T1 the temperature of the hot source. So, accordingly, as higher T2 is for a same T1, lowest is the efficiency of the engine. But, the...
  10. T

    What is the equation for Cp in terms of R for an adiabatic charging process?

    Hi guys, i just discovered this forum and this is my first post so apologies if i made any mistake with the how I am suppose to structure a thread. but nontheless any help would be greatly appreciated! cheers 1. Homework Statement 4. A 250mm diameter insulated cylinder (see figure below) is...
  11. trigger701

    What moves the piston in a Carnot heat engine?

    Hi everyone, I have been looking at Carnot heat engines in a bid to better understand entropy, and I can't figure out how it actually does work. Why does the piston move? In some diagrams I have seen weights being removed from the piston, reducing the pressure at constant temperature and...
  12. U

    Examples of systems which cannot receive work adiabatically?

    In Principles of General Thermodynamics, Hatsopoulus and Keenan (p 442) make the following claim: What, however, would be some physical examples of such a system?
  13. S

    Role of Quantum Mechanics and Thermodynamics in solar cell?

    What is the role of Quantum Mechanics and Thermodynamics in solar cell operation? Is quantum mechanics the photovolatic effect, and thermodynamics the cell efficiency?
  14. U

    Is Thermodynamics the hardest science?

    I'm currently reading thermodynamics which is only the second volume of all the physics course that I'm planning to read. So for the math in it is just killing me literally. Mechanics was relatively easy but this subject is just too freaking hard. All these partial differential equations and...
  15. O

    Book on thermodynamics for International Physics Olympiad?

    Hi! I'm a junior in high school studying for the IPhO and I've started learning thermodynamics as part of my preparation. I have a guide to the exam that says things like this will be tested: Carnot engine Kirchhoff's law Wien's law Stefan's law Stefan-Boltzmann law Newton's law of cooling...
  16. C

    Show that (du/dv)t=T(dp/dT)v-p - please explain

    Homework Statement Show that (du/dv)T = T(dp/dt)v - p Homework Equations Using Tds = du + pdv and a Maxwell relation The Attempt at a Solution I've solved the problem, but I'm not entirely sure my method is correct. Tds = du + pdv ---> du = Tds - Pdv - Using dF=(dF/dx)ydx +(dF/dy)xdy...
  17. Ravi Singh choudhary

    Velocity of liquid from bottom pinhole of closed container

    What I know: Below link is about Torricelli's law. Velocity of liquid coming out of bottom of the tank i.e comes after using Bernoulli's equation square root of (2*g*h*) where "h" is height of fluid in the container and "g" is acceleration due to gravity...
  18. Ravi Singh choudhary

    I What will be the flow direction?

    I guess there would be no flow in case 2; case 3 seems easy to me applying fluid mechanics principle; flow will be 1 to 2. But I doubt case 1; it is not in thermal equilibrium ? Pls help
  19. 1

    I Understanding the Definition of Cp and its Relationship to Cv: Explained

    Hi all, I'm working through a derivation of the general relationship between Cp and Cv and there's one point which is confusing me. I understand that and and that this implies the following: but isn't this equal to 0? Shouldn't the two partial derivatives on the right...
  20. bananabandana

    I Energy levels generally invariant under fixed V, changing T

    Why is is true that for a given system, if I fix the volume and increase the temperature, you'd expect the occupancy of the energy levels to change, but not the levels themselves? Can I think of this in terms of the fact that the boundary conditions for the solution of the TISE are fixed, such...
  21. V

    How to Calculate Work Done by a Gas in Thermodynamics?

    Homework Statement Please see the attached image Homework Equations pv=nRTThe Attempt at a Solution i don't know how to calculate the work done by the gas in the question and i calculated the change in internal energy.
  22. Willfrid Somogyi

    Heat Extracted and Delivered to Reservoirs in a Heat Engine

    NO TEMPLATE---MISPLACED HOMEWORK So it seems like a pretty simple question, and in all likelihood it is, but my lecturer somehow managed to miss this bit in his lecture notes. A heat engine operates between 500K and 300K with 20% of the efficiency of Carnot engine operating between the same...
  23. S

    Thermodynamics and heat capacity

    Homework Statement A 10.0 g sample of solid platinum is placed in a large, sealed vessel at a sufficiently low pressure that the platinum is able to sublimate directly to a gas. Some thermodynamic properties of platinum at low pressure are given in the following table. Molar mass, M - 195...
  24. M

    Thermodynamics Gases: Final Temp, Work, Internal Energy, Q

    Homework Statement two cubic ft, of air at 85 f and 13.9 psi, compress to 115 psi. What is the final temp, the work, the internal energy "delta u", and Q Homework Equations well i don't have any equations, i am asking for the equations The Attempt at a Solution i don't know how to approach to...
  25. Oribis

    Is this reaction reversible?

    Homework Statement Hello, new here! I have a question regarding reversible or irreversible expansions in regards to figuring which equation is needed to figure out work, W. For starters, here is the question: One mole of an ideal monatomic gas is expanded from an initial state of 3 atm and 500...
  26. Erenjaeger

    Ice melted by impact of lead bullet

    Homework Statement A 3.20 g lead bullet at 28.0°C is fired at a speed of 210 m/s into a large block of ice at 0°C, in which it becomes embedded. What mass of ice melts (g)? Homework Equations I thought that the KE of the bullet would be transferred into heatThe Attempt at a Solution I used...
  27. Nemo's

    What is the exit steam velocity?

    Homework Statement Steam, at 15 bar and 280oC, enters a nozzle with an initial velocity of 125 m/s. The steam enthalpy at the exit section is 2800 kJ/kg and the heat loss is 25 kJ/kg. What is the exit steam velocity?. Homework Equations 1)Qin - Qout = m [h2-h1+((c22-c12))/2] 2)h = Pv + u...
  28. K

    Thermodynamics Cycle: Gas Temperature and Work Calculation | Homework Solution

    Homework Statement I.The gas is heated at constant pressure until the volume is 4.4L at point B II. The gas is cooled at constant volume until the pressure decreases to 1.2 atm III. The gas undergoes an isothermal compression back to point A a) Find the temperature at Point A,B,C b) Find the...
  29. T

    Grade 11 Thermodynamics Question

    Homework Statement You add 50 g of steam at 150 degrees centigrade to 50 g of ice at negative five degrees centigrade. What is the final temperature? Homework Equations Q = mLfv Q = mcΔT The Attempt at a Solution Qg = Ql Q1 + Q2 = -Q3 - Q4 mLf + mcΔT = -mLv + mcΔT [ΔT will be negative, making...
  30. S

    I Condensation inside the walls of a bottle

    When I leave a closed half full bottle of water overnight, the next morning I find condensation on the inside walls of the bottle BUT! Only where sun light has reached it! I thought this was widely known and easy to explain, but I've been looking on the Internet for a while and haven't found a...
  31. L

    Thermodynamics - Piston-and-Steam-Table-Type Question

    Homework Statement [/B] An insulated cylinder containing water has a piston held by a pin. The water is initially saturated vapour at 65°C and a volume of 5L. The piston has a total mass of 10kg, its area is 0.003 m^2 and the atmospheric pressure is 100kPa. The pin is then released, allowing...
  32. G

    Kelvin thermodynamics temperature scale

    The thermal efficiency of a reversible heat engine is solely a function of the temperature of the two reservoirs. η = f(θH,θC) = 1 - (QC/QH) (QC/QH) = 1 - f(θH,θC) (QC/QH) = Ψ(θH,θC) The simplest function that can be used is T1/T2 (QC/QH) = T1/T2 In order to define the Kelvin scale we assign a...
  33. V

    A problem from thermodynamics -- Freezing of water at 273 K and 1 atm

    Homework Statement Freezing of water at 273 K and 1 atm which of the following is true for the above thermodynamics process p) q=0 q)w=0 r)ΔSsys<0 s)ΔU=0 t)ΔG=0 Homework Equations none[/B]The Attempt at a Solution [/B] i got r, s ,t since the reaction happens at constant...
  34. T

    Thermodynamics turbocharger question

    Homework Statement A 10 L truck engine has a volumetric efficiency of 100%. It has a turbocharger which increased the mass flow of air and its pressure by a factor of 2 when the engine is running at 4300 rpm. Find the turbocharger rpm, efficiency, and the temperature of the air leaving the...
  35. V

    Doubt from second law of thermodynamics

    qrev/T = ΔS here what does ΔS signify?does it mean change in entropy of system or surroundings? how is entropy of system,surrounding and universe related to each other and which entropy is used in gibbs free energy equation?
  36. physea

    Confused with the energy equation in thermodynamics

    Hello I am confused with the energy conservation equation in thermodynamics. Is it U2 - U1 = Q - W ? This is what most books say. Or is it H2 - H1 = Q - W ? Which should I use to solve problems? For example we have a gas with U1 and P1V1 (which makes H1). After a process, we have Q...
  37. G

    Heating upon sudden elastic compression of material

    Hello, I would expect the heating of an elastic material upon sudden elastic compression to be given simply by the first law of thermodynamics, i.e. Delta Q=Delta U + P Delta V where P is constant since the compression is applied suddenly as in a square-wave pressure pulse (this is equivalent...
  38. Tengo Preguntas

    Do White Holes Violate 2nd Law of Thermodynamics?

    I have heard (read) much debate over the fundamental problems with white holes, mainly that they violate Thermodynamics by increasing entropy. However, I have also read that a black hole bends space-time enough to "connect" somewhere else as an Einstein-Rosen Bridge. So if the exact same event...
  39. C

    Rate body temperature increases given rate of heat transfer?

    Homework Statement Suppose you walk into a sauna that has an ambient temperature of 57.0°C. Calculate the rate of heat transfer to you by radiation given your skin temperature is 37.0°C, the emissivity of skin is 0.95, and the surface area of your body is 1.60 m2. I solved this first part and...
  40. M

    Quasi-static and reversible processes in thermodynamics

    Too much confusion in my head about these concepts... Is every reversible process quasi static? If not, what are some examples? If process is irreversible then it doesn't need to be non quasi-static, I understand that. (eg. free expansion of the gas) Can irreversible process be quasi static...
  41. Zero-shift

    How Does Surface Tension Affect Thermodynamic Potentials in Soap Bubbles?

    For a system modelling a soap bubble, the differential work done is now given by: dW = −pdV + γdA, where γ is the surface tension and A the area. Compute new differential expressions for the potentials U, H, F, G. What are the new natural variables in each case? Are there any new Maxwell...
  42. C

    A thermodynamics polymer chain problem

    A one-dimensional polymer molecule (rubber) is chain of N links of the same length a, the links can go either forward or backward but always stay parallel to the x axis. If one denotes the coordinates of the joints are ${x_0, x_1, . . . , x_N}$ , then $|x_n − x_{n+1}| = a$. The energy of the...
  43. Zero-shift

    Thermodynamics (Closed System) questions

    If I have a closed system where mass is conserved, what constraint will this bring on the system in terms of infinitesimal quantities. What conclusions can I then draw about the phases at this kind of equilibrium? Suppose we had an isovolumic, isothermal change, how would I have to alter my...
  44. F

    Thermodynamics Conceptual Question

    Hi! I'm new to the forums, so I apologize in advance if I'm posting my question in the wrong section. I'm studying thermodynamics right now, and I came across this sentence from my book: Homework Statement "When energy is added to a system and there is no change in the kinetic or potential...
  45. D

    Understanding Pressure Changes in Thermodynamics: Explained with an Example

    Homework Statement I'm doing a class on thermodynamics and energy and well there's this chapter about pure substances and subcooled liquids, saturated liquids, superheated, etc. stuff like that. The chapter begins by showing a piston-cylinder in an initial state containing liquid water and a...
  46. P

    I Two blackbodies at two foci inside an ellipsoidal shell

    Let's consider two spherical blackbodies at two foci inside an ellipsoidal heat-reflecting shell. Consider the situation that they both have different radii and that their temperatures are such that they emit the same power. Thus, the surface power flux density of each is inversely proportional...
  47. K

    Thermodynamics and waves problems

    Homework Statement 1. A gas expands as shown in the graph. If the heat taken in during this process is 1.02 × 10^6 J, the change in internal energy of the gas (in J) is 2. One mole of an ideal gas is held at a constant pressure of 1 atm. Find the change in volume if the temperature changes by...
  48. C

    Thermodynamics - Two gases in a container

    Homework Statement Two kilograms of air at 5 bar, 350 K, and 5 kg of carbon monoxide, initially at 4 bar, 450 K, are confined to opposite sides of a rigid, well-insulated container by a partition. The partition is free to move and allows conduction from one gas to the other without energy...
  49. I

    Question about where a thermodynamics formula comes from

    Homework Statement How do we obtain: w = q - Δh Homework Equations The Attempt at a Solution If you neglect the second half of the SFEE and simplify we get: What is the next step from the last line in the above image to w = q - Δh I mean dw/dt = dq/dt - Δh so if we multiply by dt we...
  50. S

    Question about Reversible Engines and Carnot Efficiency

    Homework Statement I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. The highlighted parts of the image are where I am having some issues. I...
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