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. WMDhamnekar

    MHB What are some questions about thermodynamics and their potential answers?

    Hello, Here are the questions with unknown answers. (These chemistry questions are other math topics.) 1) At 1 bar, the boiling point of water is 372.78 K. At this temperature and pressure, the density of liquid water is $958.66 kg/m^3$ and that of gaseous water is $0.59021 kg/m^3.$ What are...
  2. L

    Engineering Why is the first law of thermodynamics useful in developing these equations?

    why it is first law of thermodynamics useful in developing the non-flow energy equation and steady-flow energy equation. First Law Equation (FLE) = 1 1.1 Non-Flow Equation = 2 Steady-Flow Equation = 3 Specific Entrapy of Steady-Flow 4 Mass Flow 5 I understand (i think) but can't explain...
  3. B

    Engineering Steady flow energy equation in Thermodynamics

    I am looking for help on the following: a) Given the system shown in the figure below, derive the steady flow energy equation from first principle. b) Again using first principles, show how the energy equation would change for the case when the system is unsteady. I am trying to learn this...
  4. Gaby

    The first law of thermodynamics for open systems

    Please see enclosed my calculations for parts 1-3. I am stuck on the final part of of a 4 part question, any help or guidance would be very much appreciated, thanks.
  5. Amaterasu21

    I How Does Relativity of Simultaneity Clash w/Thermodynamics?

    In special relativity, observers can disagree on the order of events - if Alice thinks events A, B and C are simultaneous, Bob can think A happened before B which happened before C, and Carlos thinks C happened before B which happened before A - provided A, B and C are not causally connected, of...
  6. mcastillo356

    First law of Thermodynamics and energy conservation

    Hi PF! I don't understand the sentence: on one side says the energy is preserved, and, at the end, the total energy of the system will change if ##W## or ##Q## is added: ##\Delta{U}=Q+W##. Greetings!
  7. E

    "Where’s your second law of thermodynamics now?"

    Prof. Tong used the Liouville theorem to prove the Poincaré recurrence theorem in his notes, that given an initial point ##P## in phase space, for any neighbourhood ##D_0## of ##P## there exists a point ##P' \in D_0## that will return to ##D_0## in a finite time. To illustrate the theorem, he...
  8. Tony Hau

    Problems understanding the 2nd law of thermodynamics

    So my professor says that the implication of 2nd law of thermodynamics is that high quality energy will be degraded into low quality energy. By high quality energy he means something like coal or fuel. By low quality energy he means something like heat entering the cold resevoir in a heat...
  9. T

    Help with this thermodynamics and entropy question please

    So I've answered the first question and I got a final temp of 42.06 Celsius. Now for this second one, I don't know why I am getting it wrong: Im doing 0.215*ln(315.06/291.46) + 1*ln(315.06/319.91) But it says I am wrong. What about my process is faulty?
  10. nomadreid

    Exploring "Thermokinetics": What Is It?

    Wikipedia https://en.wikipedia.org/wiki/Thermokinetics says that "thermokinetics" studies the rate of chemical decomposition, whereas a dictionary https://www.yourdictionary.com/thermokinetic gets no further than saying that it combines thermodynamics and kinetics, and a book on it...
  11. nomadreid

    I Ratio of a real value to the max theoretical value: what term to use?

    If the Summary is not clear, the following is an example translated from: https://telecombloger.ru/7335 '... air conditioning systems. For example, the efficiency of a compressor is about 85%. The remaining 15% is spent on friction, oil movement, overflows, heating, etc. The efficiency of the...
  12. M

    Types of thermodynamics processes that happen in solids or continuum medium

    What are the types of thermodynamics processes that happen in solids or continuum medium
  13. P

    Interpreting a thermodynamics formula using a picture

    I notice that ##pv=t## looks like the ideal gas law but with ##T## in units of energy. I know that ##pV = \text{constant}## means that the pressure of a gas decreases as you expand it (Boyle-Mariotte's law), explaining for instance how we breathe. I guess I could put everything in words even...
  14. Hamiltonian

    Work done by irreversible and reversible processes

    I am not able to follow the derivation of work done in a reversible and irreversible process as I don't get why the work done should be different in the two processes. a reversible process is said to be a process that occurs infinitesimally slowly and an irreversible process goes from initial to...
  15. Hamiltonian

    First law of thermodynamics and the work done on a system

    The first law of thermodynamics states that the change in the internal energy of a system equals the net heat transfer into the system minus the net work done by the system. In equation form, the first law of thermodynamics is ΔU = Q − W. in the mathematical expression of the first law of...
  16. aspodkfpo

    Dodgy solution for a thermodynamics problem?

    https://www.asi.edu.au/wp-content/uploads/2020/07/ASOE_Physics_2019-answers.pdf Question 14 B) Re: " The graph of force per area vs amount of gas will change, as the pressure is increasing due to increasing temperature, so the amount of gas in a volume at a given pressure will be decreasing...
  17. M

    Is the change in internal energy really a state function?

    Here is the figure: The answer is $$Q_A<Q_B$$ which I can show by calculation using the above equations. What's confusing to me is I thought that the change in internal energy was a state function. Which would mean since the initial and final points are the same, $$\Delta E_A=\Delta E_B$$ or by...
  18. bsharvy

    Energy Conservation and the Dragons (Game of Thrones)

    I thought I'd calculate how much heat was required to melt the Iron Throne, and then multiply that by the number of flame-gushes during the sack of Kings Landing, to get a total amount of energy expended. Then I'd convert that to calories and use the average number of calories per goat to...
  19. Rahulx084

    Thermodynamics: Single/Homogeneous Phase Differences

    #Can somebody please explain what is the difference between single phase and homogeneous phase in context with thermodynamics? #Also in the fundamental relations in thermodynamics like dg=vdp-sdT , it says this is applicable to homogeneous phase of constant composition. Isn't this equation...
  20. TechieDork

    Need help with calculating a Cv in PHYWE's Heat Capacity of gases

    I've conducted this experiment yesterday. The main goal of this experiment is to find a gas constant R and compare it with its theoretical counterpart but I get stuck in calculating a Cv so I tried to find out what's wrong with my calculations by trying to calculate a Cv from the given data...
  21. Traced

    Chemistry Thermodynamics: The molar enthelpy of a solution

    My answer is -0.40 kJ/mol. I'm having trouble understanding why the molar enthalpy of the solution is a negative number. Wouldn't this mean that the solution is losing energy? If the temperature of the water heats up from 20 degrees Celsius to 36 degrees Celsius shouldn't the final answer be...
  22. P

    Heat engine that uses a rubber band (Thermodynamics)

    Nota that the path a to b is isothermal since J is proportional to L, then we can find the value of T_a and T_b using the equation of state and the figure. We have, \begin{equation} J_0=\alpha L_0T_b \end{equation} or \begin{equation} T_b=T_a=\frac{J_0}{\alpha L_0}=T_0 \end{equation} Also, by...
  23. Ron19932017

    Euler's equation of thermodynamics in free expansion (Joule expansion)

    Hi everyone, I am confused when I apply Euler's equation on the free expansion of an ideal gas. Consider a free expansion (expansion of gas in vaccum) where the volume is doubled (V->2V) The classical free expansion of an ideal gas results in increase in entropy by an amount of nR ln(2), a...
  24. TytoAlba95

    Chemistry Thermodynamics: Reduction Potential question

    The answer key says the correct option should be a, but I think it should be b. Because Y has a reduction potential same as the element B. An element is a good reducing agent only if its reduction potential is negative or less positive.
  25. M

    Is the Second Law of Thermodynamics Falsifiable?

    My question relates to whether the 2nd law of thermodynamics is a an empirical or mathematical law. If we can reason purely from the laws of statistics that entropy can only increase, then the 2nd law of thermodynamics cannot be falsifiable and therefore shouldn't be considered a scientific...
  26. N

    Thermodynamics: phase change and latent heat problem

    The second question is where I'm lost. The answer to the first question is 5.39 grams. The second is 10.3 grams. Until I saw the answer I was setting the equation up as if some of the original steam had condensed. But it appears that some of the original water changed into steam. Is it necessary...
  27. T

    Exploring the Grand Partition Function for an Einstein Solid

    $$Q_{(\alpha, \beta)} = \sum_{N=0}^{\infty} e^{\alpha N} Z_{N}(\alpha, \beta) \hspace{1cm} (3.127)$$ Where ##Q## is the grand partition function, ##Z_N## is the canonical partition function and: $$\beta = \frac{1}{kT} \hspace{1cm} \alpha = \frac{\mu}{kT} \hspace{1cm} (3.128)$$ In the case of an...
  28. vjrajsingh

    Non-equilibrium thermodynamics

    Biological systems act as dissipative structures and obey the universal laws of thermodynamics in spite of being open structures as they follow non-equilibrium thermodynamics. In accordance with the second law, entropy generation occurs. Is it possible to limit the entropy generation in a...
  29. A

    What is the -1st law of thermodynamics?

    The so called -1st (Minus First) law of thermodynamics, I believe states that information cannot be destroyed, or something along those lines. Does anyone know where I can read more about it? I think I've heard Dr. Leonard Susskind talk about it but it's been hard to find the video or any other...
  30. J

    Ipho 1987, thermodynamics problem: Moist air ascending over a mountain range

    I'm struggling with explanation of part 3. I don't know why they are using adiabatic equation while the gas is constantly heated by condensating vapour. While we are deriving adiabatic equation we use the fact, that there is no additional heat put into the system. Thank you in advance.
  31. J

    Exploring Entropy: A Systems Engineering Perspective

    As a systems engineer I have thought a lot about entropy in trying to get a better intuitive sense for what it is, at a more macro level than it is usually discussed. I have some ideas and am looking for a forum to present and explore them with others. I wish to discuss more from an...
  32. Amaterasu21

    At what size is kinetic energy no longer related to temperature?

    Hi all, I've read so many times that "temperature is a measure of the average kinetic energy of the molecules in a substance," or sometimes "particles" to encompass atoms and ions too. But how big can "molecules/particles" be before their kinetic energy is no longer relevant to temperature? If...
  33. L

    Teaching Thermodynamics with minimal math

    Thermodynamics is an interesting subject but all too often students think of it as solving math problems. And indeed most of the problem solving involves calculations which can be quite in-depth, requiring knowledge of calculus. I have been looking for ways to deliver thermodynamics principles...
  34. J

    Thermodynamics Problem: Finding Heat Transfer

    I have come across this problem from this booklet: https://www.ioc.ee/~kalda/ipho/Thermodyn.pdf
  35. Rongeet Banerjee

    Calculating Cp for Ideal Gases using Thermodynamic Relationships

    In this particular Question according to Meyer's formula,the value of Cp should be (8.314+5) i.e. 13.314 .But that option is missing. There is another approach to this problem by finding the Adiabatic Coefficient and then finding Cp.I have no problem with that approach. But my initial doubt...
  36. Refrigerators and Carnot Cycle (Sequence of 5 steps) #14

    Refrigerators and Carnot Cycle (Sequence of 5 steps) #14

    Refrigerators run on Carnot cycle. It is like a heat pump that operates on the reversed Carnot cycle. It utilizes the evaporation of the refrigerant to absor...
  37. densephysicist

    Calculus problem regarding Thermodynamics HW (entropy for C2H5OH at 348K)

    Summary:: Seems simple but has me stumped... [Thread moved from a technical forum, so no Homework Template is shown] Hello! I am struggling to use an equation given to me. To provide some context, I am trying to work out the entropy for C2H5OH at 348K. Using provided tabulated data, the...
  38. Second Law of Thermodynamics and Heat Engines #11

    Second Law of Thermodynamics and Heat Engines #11

    The Second Law of Thermodynamics is not an easy topic. However, if you understand the concept of direction of thermodynamic processes and heat engines, you w...
  39. S

    Engine working between multiple temperature baths worse than Carnot

    Let the new engine, NE, extract heat from a certain subset of these baths, and let heat obtained from the ##i^{\rm th}## bath be denoted by ##Q_i##, and let the heat rejected to the ##j^{\rm th}## be denoted by ##Q_j##. Let the engine perform an amount of work ##W##. Now right beside this...
  40. B

    Heat distribution in a piece of glass receiving protons

    First of all, I didn't know whether to pick this subforum or the engineering/compsci one, I understand this might need to be moved to a more appropriate subforum. The general approach is fairly obvious, use implicit method to construct the tridiagonal matrix for Thomas method and solve. However...
  41. J

    The Physics of cooking breakfast (basic thermodynamics)

    I eat eggs, ham, peppers, and a pancake for breakfast. I cook the ham and peppers at the same time. For purposes of this question, I have the eggs and the pancake figured out. Given a gas stove, a small, nonstick aluminum frying pan (with lid) and corn oil; If my goals are (in order of...
  42. A

    Gas - cylinder - piston problem

    Summary:: Seeking explanation to classical gas - cylinder - piston problem, not the solution. Problem 1.15 from 7th edition of Introduction to Chemical Engineering Thermodynamics by Smith, Van nes and Abbot) Classical problem, given: - gas in a confined cylinder - piston with weight is placed...
  43. T

    Thermodynamics -- Calculations for heating water up

    A thermal flask with water of temperature 90c is placed out in room temperature 20c, sealed. How long before it reaches 55c? outer radius and height: 5cm, 25cm volume of water is 1litre. R = 0.5 Km2/W using this equation to solve it combining these two and integrating with respect to T...
  44. Y

    Why use c_p and not c_v as specific heat - Thermodynamics

    Hey all, I am working on a problem that goes like this: The cargo space of a refrigerated truck whose inner dimensions are 12 m 3 2.3 m 3 3.5 m is to be precooled from 25°C to an average temperature of 5°C. The construc- tion of the truck is such that a transmission heat gain occurs at a rate...
  45. I

    Question about thermal physics -- Ice cubes melting in water

    First, I calculated the heat required for the ice to melt: Q=mLf Q=0.150×330 Q=49.5 J Then, I calculated the final temperature of the water by forming the following equation: Q=mcΔT −49.5=(0.15+0.35)×4200×(Tf −80) Tf=80.0 degrees Celcius But the answer says 32 degrees Celsius.
  46. H

    I Thermodynamics Differentiating logarithms

    <mentor: change title> In thermodynamics, there is a function which, for the three variables x, y, and z, can be given as ##G = xG_x+yG_y+zG_z + N[x\ln(x) + y\ln(y)+ z\ln(z)]+E(x,y,z)## where G_x, G_y, G_z, and N are some constants and E is some arbitrarily complicated term. There is a...
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