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. A

    Conceptual thermodynamics problem about ammonia executing a Carnot cycle

    Is there a mathematical explanation for why the work done in the condenser (in process 2 to 3) is zero? I am aware that ammonia does not expand or compress in the condenser, only changes phase, but without knowing that the process takes place in a condenser and only considering the graph...
  2. A

    Conceptual thermodynamics question regarding specific heat ratio

    The solution can be found at https://study.com/academy/answer/an-insulated-rigi... After using the two equations I can't see why (h2-h1)/(u2) should equal (T2)/(T1). Can someone explain why specific heat ratio is equal to temperature ratio?
  3. jackdale

    The Second Law of Thermodynamics and the Stefan-Boltzmann Law

    I have a question about the Second Law of Thermodynamics and the Stefan-Boltzmann law. These quotes are from http://www.ces.fau.edu/nasa/module-2/correlation-between-temperature-and-radiation.php “The Stefan-Boltzmann law, a fundamental law of physics, explains the relationship between an...
  4. P

    Thermodynamics Problem: Reversible and Irreversible Processes

    Attempt at A Solution Problem 1 Reversible Process - A cylinder of ideal gas at pressure P is in mechanical equilibrium with a piston of area A driven by a spring of force F = PA and thermal equilibrium with a reservoir of temperature T. The piston is moved a small distance dx toward the...
  5. VVS2000

    Fundamental equation (thermodynamics) from Euler's equation

    by substituting all values in the euler equation you get most of the terms in the fundamental equation but not (N/No)^-(c+1) How do you get this term?
  6. M

    Thermodynamics Problem: Cylinder-Piston System with Friction

    Hi guys, First of all I'm sorry for my bad english I'll try to be as clear as possible. I have tried to solve this problem to understand the First Law of Thermodinamics: Q+L=ΔE_t In fact I know L (in the current convention) is the work which the envirorment does on the system but I don't...
  7. S

    High Energy Introductory notes on AdS/CFT or black hole thermodynamics

    I am looking for a book/notes on the topics mentioned in the title that would be accessible to an undergrad. I have a background in grad quantum and statistical mechanics, but most resources I found on those topics assume a familiarity with QFT, string theory, gauge theory, and general...
  8. B

    Thermodynamics: calculate thermodynamic derivative from data?

    I don't understand how to use output from an NPT molecular dynamics simulation to compute a thermodynamic derivative. I need to compute this (where "d" is a partial derivative, "T" is a subscript that means, "at constant temperature," and "E" is internal energy): -(dE/dV)T I have a simulation...
  9. Sokolov

    Integration of inexact differentials in Thermodynamics

    In Thermodynamics, I have seen that some equations are expressed in terms of inexact differentials, ##\delta##, instead of ##d##. I understand that this concept is introduced to point out that these differential forms are path-dependent, although I am not clear how they can be handled. So, are...
  10. Y

    Engineering Find out the percent exergy loss

    Problem, with state values, and pie chart (Fig 4.20) showing answers: ^ This shows the system in question (Kapitza Liquefaction System). Methane gas enters into the compressor (c), then goes through the first heat exchanger (HX1). Some of it (z) gets routed to the expander (exp). Afterwards...
  11. WateryFungi

    Engineering Thermodynamics - Control Volumes find final temperature

    Hi I'd like to know if my current approach to the problem has any issues. My attempt: Balancing the equation: Qin + Win +mΘout = Qout + Wout + mΘout Qin+m(hin + v2in/2 + gzin) = m(hout + v2out/2 + gzout) Wflow + ΔU + m(hin) = m(hout) I factored out the mass: wflow + Δu + hin = hout And I used...
  12. A

    Thermodynamics energy balance for control volume

    Why is energy balance for a control volume dE/dt = dQ/dt-dW/dt-dm/dt(ΔH+ΔKE+ΔPE) 0 = dQ/dt-dW/dt-dm/dt(ΔH+ΔKE+ΔPE) whereas for other systems it is ΔE =Q-W-(ΔU+ΔKE+ΔPE) 0 = Q-W-(ΔU+ΔKE+ΔPE) with enthalpy, h = u +pv, replaced by only the internal energy? How is the pv term accounted for...
  13. M

    Engineering Thermodynamics - Second Law: 2 Heat Engines Connected Between 3 Metal Blocks

    Hi, I posted a similar question recently and gained some insight on these types of problems. However, I am slightly stumped on how to approach this variation of the problem. So I know that: - there is no net change in enthalpy of the blocks and the engine as the processes are reversible -...
  14. M

    Thermodynamics Problem: Heat Engine Between Two Blocks

    Hi, I am quite confused about how to approach this problem. I have seen variations of this problem where there is a heat engine between two blocks, but in this case the surroundings are massless, so I don't believe that approach will work here. Method: I have first started with the case that...
  15. obstinatus

    Isothermal pressure change in a U-shaped tube

    Hi, just reviewing some thermodynamics from the textbook by Sears and Salinger, having a hard time conceptualizing this one. It's an isothermal change in pressure, so the volumes of the mercury and the air both change to reach equilibrium, but if it's a "good vacuum pump", then won't the right...
  16. C

    Thermodynamics help please -- Air passing through a gas turbine system

    Summary:: NO TEMPLATE BECAUSE THIS HOMEWORK PROBLEM WAS MISPLACED IN A REGULAR FORUM Cant do part c, using the steady flow equation I am confused how to continue. Please help! Mainly confused as to what heat transfer loss represents in the steady flow equation and where to go to find the...
  17. Anon_Miner

    Where do I put this Server Room's air exhaust?

    Hey guys. I have a room which i want to use as a server room. the devices need to work 24/7 and they get pretty hot. so it is imperative to keep the room cool otherwise the devices will be damaged. I have an air vent to bring cold air into the room for the devices so their fans can suck in cold...
  18. Robert DeVries

    Trouble with fluid thermodynamics and nuclear thermal rockets

    Summary:: In need of help determining the exhaust velocity of a rocket nozzle given temperature and propellant molar mass Greetings and salutations! My name is Robert DeVries, world builder extraordinaire. I have come with questions in search of answers. So for the last few days I've been...
  19. Z

    Thermodynamics: find the change of internal energy, the work and Q

    According to the first principle of thermodynamics: ΔU = W + Q Also noting that: W = -P⋅ΔV (Question: This P is the initial pressure or the final?) To find V2: (P1⋅V1) / T1 = (P2⋅V2) / T2 → Therefore, (P⋅V1) / T1 = [(P/5)⋅V2] / T2 → (P⋅V1) / T1 = (P⋅V2) / (5⋅T2) → V2 = (5⋅T2⋅V1) / T1...
  20. Rahulx084

    Thermodynamics -- Temperature of a Heat Source?

    In heat engine we define a heat source from where heat is transferred to the system, we say that heat source has a temperature ##T_h## , When we define a Carnot heat engine, the first process we have is an isothermal expansion and we say heat has to come in system through this process and here...
  21. T

    1st Law of thermodynamics : moving reference frame

    I'd like to apply the 1st law of thermodynamics in a reference frame (RF) moving with constant velocity. We have: ##\Delta{}E = E_{in} - E_{out}## I am limiting myself to rectilinear motion. Suppose we are in a RF moving with a constant velocity ##V##. Let the system consist of a mass ##m##. The...
  22. E

    Confused about use of external vs internal pressure in thermodynamics

    I've learned that ##W = -\int{P_{ext} dV}##, and only during a reversible/quasi-static process where ##P_{int} = P_{ext}## can we write the work done on the gas in terms of the internal pressure (and consequently use ##PV=nRT## etc. which apply to the internal gas). However, a lot of sources...
  23. E

    Ignoring the acceleration of a piston in thermodynamics

    I was just reading a set of thermodynamics lecture notes and came across the following In most thermodynamics problems I have done, it is indeed assumed that the piston does not accelerate so we can simply equate forces on the piston. However, I don't fully understand the line of reasoning...
  24. C

    B Irreversible expansion of gas against gas

    Let's say I have a liter of gas at pressure of 4 atm and T=900K. I use it to move perfect massless frictionless and insulative piston to compress a liter of 1 atm, T=300K gas. When the pressure on both sides is equal and the piston stops moving, will the temperature on both sides of the piston...
  25. T

    Adiabatic approximation in the derivation of the speed of sound

    The speed of sound in a gas at temperature T is given to be ## v=\sqrt{\frac{\gamma RT}{M}}##, where ##\gamma## is the adiabatic exponent, R is the gas constant and M is the molar mass of the gas. In deriving this expression, we assumed that the compression and expansion processes were so fast...
  26. F

    Temperatures of the hot source and cold sink in a heat engine

    Hi, I was just wondering about the efficiency of a cycle that is not Carnot cycle. In that case one should use \eta = 1-\left|\frac{Q_{\rm out}}{Q_{\rm in}}\right|, where Q_{\rm in} and Q_{\rm out} are the amounts of heat absorbed and released during the cycle. For instance, I guess that in...
  27. H

    Thermodynamics: Why does salt lower the melting point of ice?

    There was a question on "Why salt lower the freezing point of water?"I found the following answer."Thermodynamics teaches that a loss of entropy can be overcome by a gain in so called enthalpy". The loss of entropy by freezing the solution canbe over come at temperature much below 0 degree C...
  28. C

    Thermodynamics - Change in temperature for heated slabs of steel

    Just started this topic so I'm not sure if this is the correct way to solve this, any help would be appreciated. mass of object x change in temp x specific heat capacity= heat change in temp= heat/(mass of object x specific heat capacity) Mass= 700kg Specific heat capacity of steel= 0.42kJ/kgC...
  29. Stephen Bulking

    Thermodynamics problem involving engine efficiency

    Q2: An engine has power of 26.5 kW, needs 9 kg coal during an hour for energy. The heat capacity of coal is 7800 cal/g. Define the engine’s efficiency. Qh= mcΔT = 9000x7800xΔT ( stuck) P=26.5kW(is this the power output of the engine in an hour?) If only I could find ΔT, thenI would be able to...
  30. WhiteWolf98

    Finding Isentropic Enthelpy, knowing Isentropic Entropy

    A short background: My question focuses solely on the part of the refrigeration cycle to do with the compressor, where the cycle begins. The first state is before the refrigerant enters the compressor, and the second state is after the refrigerant leaves the compressor. My goal is to obtain...
  31. A

    Does classical statistical physics predict newer things vs. thermodynamics?

    I'm wondering if the passage from a classical thermodynamic theory, i.e. which does not resort to an atomistic theory and methods of probability and statistics, to classical (i.e. non-quantum) statistical mechanics, led to new discoveries and especially if it was able to explain properties of...
  32. Physics345

    Entropy and the Laws of Thermodynamics

    Hello everyone, I have to write a paper about entropy and how it relates to the laws of thermodynamics, energy, and work. I have taken a deductive approach starting from the zero-th law to the second law of thermodynamics as follows. Entropy is the disorder of a system (Class Video, 2019)...
  33. C

    Is Specific impulse indicative of performance as a gun propellant?

    Black powder has specific impulse of around 80s, while rocket candy has up to 130s of specific impulse. Does that mean I could replace the propellant in a BP cartridge with 80/130 of the weight in rocket candy and obtain the same performance in an idealized gun? (as in without considering...
  34. WhiteWolf98

    Clausius-Clapeyron equation to estimate sublimation pressure of water

    Before this question, the questions were about the Clapeyron equation, and how to estimate ##\Delta s##. I'm completely put off by this question however, and don't know where to start. I've found that the triple point of water is at ##0.01°C##, and there is indeed data in the table for...
  35. K

    Gibbs' theorem and partial molar volume

    In the chemical engineering text of Smith, VanNess, and Abbott, there is a section on partial molar volume. It states that Gibbs theorem applies to any partial molar property with the exception of volume. Why is volume different? In other words, when evaluating the partial molar volume of a...
  36. P

    Temperature and non-equilbrium thermodynamics

    Suppose we have a body that isn't a black body, but has an arbitrary emission spectrum. In the general case, can the radiation from this body be characterized as having a temperature, and if so, how? If not, what conditions are needed to make the concept of temperature meaningful in this case?
  37. R

    Question about the first law of thermodynamics

    In thermodynamics, the internal energy (U) is the function of the volume (V) and temperature (T), U = U (T). Therefore, according to the mathematics, dU = π dV + Cv dT, where π is internal pressure and Cv is the constant volume heat capacity. Meanwhile, according to the 1st law, dU = δ w + δq...
  38. yecko

    Why is the change in entropy of a heat pump in one cycle equal to zero?

    as it is not ideal, total change of entropy > 0 entropy loss of hot reservoir > entropy gain of cold reservoir why would the change in entropy of the heat pump in one cycle equals to zero? thank you
  39. Sai Maurice

    Temperature change brought about by radiation

    I tried modeling the problem quite a few ways. one was to say that the difference between the heat emitted by the room and the heat emitted by the bulbs would equal the heat absorbed by the room, and that could allow us to calculate temperature. This did not work. I'd appreciate your help
  40. P

    Calculate internal temperature and energy changes

    Question (These are incorrect values) Attempt I used and then found the respective change in temperature. However for the last question I have no idea, do I sum up the net change in temperature and use But then what is the work and how do we figure it out?
  41. Javier0289

    Thermodynamics - How to find an "adiabat"?

    I tried this... but I'm not sure if I'm doing it right or maybe there's a simpler way. Thanks for your time or help :) The fundamental relation is: $${S \over R} = {UV \over N} - {N^3 \over UV}$$ but I used $$s=S/N, u=U/N, v=V/N$$ to obtain $${s \over R} = uv - {1 \over uv}$$ then I did...
  42. A

    AIK, this is the best I can do for you.

    Carnot's postulate: one cannot build an engine whose sole effect is to transfer heat from a cold body to a hot body. How granted this postulate can I prove that no engine beats Carnot's engine? From this postulate, I can conclude that work must be done from the surroundings and that Carnot's...
  43. Baibhab Bose

    Phase transition between two phases with different Cv

    I actually can't figure out what kind of phase transition it is and how to proceed through..!
  44. S

    How to calculate the transition temperature in this problem?

    Summary: The transition Sn(s, gray) ⇌ Sn(s, white) is in equilibrium at 18°C and 1 atm pressure. If ΔS = 8.811K mol for the transition at 18°C and if the densities are 5.75 g/cm3 for gray tin and 7.28 g/cm3 for white tin, calculate the transition temperature under 100 atm pressure The...
  45. Dan13

    How Does Expansion Affect Internal Energy in a Monatomic Ideal Gas?

    Problem Statement: A monatomic ideal gas expands from 100cm³ to 200cm³ at a constant pressure of 1.0 × 10⁵ Pa. Find the change in the internal energy of the gas. Relevant Equations: Included in my attempt at a solution
  46. alexmahone

    Textbook containing the Rankine cycle (Thermodynamics)

    I'm taking an online course that covers the Rankine power cycle, that, unfortunately, isn't mentioned in any of my textbooks. Do you guys have a textbook that covers this cycle? Thanks
  47. A

    Does the First Law of Thermodynamics Allow for Heat Generation During Stirring?

    Consider a system composed of a gas+stirrer at state 1, Work is done on the system by a rotating shaft, the stirrer activates high speed generating a significant amount of heat. The system is undergoing a process because the set of measurable properties to define its state are changing, If I...
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