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. PaxFinnica96

    Engineering Thermodynamics: Pass-out Turbine Question

    Hello Physics Forums, I have been struggling with this question for some time now and I'm not sure my method is correct - please see attached. Any help you can give to check I'm on the right lines would be very much appreciated! Cheers, C
  2. S

    Classical Looking for Griffith-style books on mechanics, thermodynamics, astronomy

    Hello! Searching for above mentioned books for my Bsc studies. Like his style and the quantum and electro books were very well written(in my opinion) and easy to navigate through, also liked the pre-explained math tools i need for the book. Tried Goldstein and Taylor books on mechanics but they...
  3. Ale_Rodo

    I Understanding Wrev > Wirrev in Thermodynamics

    Hi, I'm an engIneering undergrad and haven't done Thermodynamics just yet. The little I know about it comes from a Chemistry course I have. Recently, I happened to struggle understanding the professor's and books' demonstration on how Wrev is always greater than Wirrev , which is a statement...
  4. burian

    I Entropy after removing partition separating gas into two compartments

    Summary:: Proving that entropy change in mixing of gas is positive definite > >An ideal gas is separated by a piston in such a way that the entropy of one prat is## S_1## and that of the other part is ##S_2##. Given that ##S_1>S_2##, if the piston is removed then the total entropy of the...
  5. Dario56

    Vapor - Liquid Equilibrium Equation (VLE)

    Most fundamental equation for VLE is $$ \mu_i^L = \mu_i^V $$ It states that for every component chemical potential must be equal in both liquid and vapor phase at equilibrium. However, in my thermo textbook, this equation is derived for isolated systems while usually when dealing with VLE...
  6. L

    Number of moles necessary to get piston back to initial position

    a) ##T_A=\frac{p_AV_A}{nR}=300.7K, P_A V_A=kL^2=nRT_A##, ##P_B S=k\frac{L}{2}\Rightarrow P_B V_B=k(\frac{L}{2})^2 \Rightarrow P_B=\frac{kL^2}{2V_A}=\frac{P_AV_A}{2V_A}=\frac{P_A}{2}##, ##W_{spring\to gas}=\int_{L}^{L/2}kxdx=-\frac{3}{8}kL^2=-\frac{3}{8}nRT_A####\Rightarrow Q=L+\Delta...
  7. L

    Finding the increase in entropy of the universe in gas expansion

    a) ##P_f=\frac{nRT_f}{V_f}=\frac{nR\frac{T_i}{2}}{2V_0}=\frac{1}{4}\frac{nRT_i}{V_0}=\frac{1}{4}P_i## b) ##Q=\Delta U=nC_V \Delta T=n\frac{5}{2}R(-\frac{T_i}{2})=-\frac{5}{4}nRT_i=-\frac{5}{4}P_i V_0## (##L=0## since the gas expands in a vacuum;Now, (a) and (b) are both correct but not (c), for...
  8. warhammer

    Entropy Change & Heat Transferred to a Gas

    By using the given relationship that S=a/T --(1) along with the equation ∫ (delta Q rev)/T=∫dS -- (2) I found out that my answer for the value of Q is mc*ln (T2/T1)*a upon equating (1) & (2). But the solution is instead given as Q=a*ln*(T1/T2). I would be grateful if someone would point out...
  9. warhammer

    To find total work done from multiple reversible processes

    The question is given in 3 parts. For first part, process is isochoric so Work done=0. We know here that at end of the process (a), T2=T1 while V remains constant (we can take it as V1) so P2=2P1. For second part, process is isothermal so T is constant. At end of process we reach P1 again from...
  10. Bolhuso

    I Galaxy redshift and thermodynamics

    I just finished rereading the great "A Brief History of Time". To me, what stands out the most in this book, is its ability to keep raising questions while you read it. This thought came up. It's been stuck in my mind for days, so I will humbly post it here to get some feedback. Please forgive...
  11. R

    Courses What do I do to catch up on Physics 1?

    I am a nanobiology student about to start her 2nd year. This year I only had 2 physics courses and I did pretty bad in both. As I start my second year I would like to be very prepared in physics since we will have way more of this subject. Are there some books or tips you have to catch up on...
  12. warhammer

    Question on First Law of Thermodynamics (Paramagnet)

    For the first part, I have expressed it in the following differential form- dU= delta (Q) + BdM Now for the second part I am having major confusion. I know that B corresponds to P and M corresponds to V as generalised force and generalised displacement respectively for a Paramagnetic substance...
  13. T

    Calculating Transient Heat Transfer in Pipes with Thick Walls

    Hi Everyone, I am looking to find how much heat can be stored in a concrete pipe of roughly 0.3-0.4m diameter, and an internal diameter of 0.05m. Air will travel through the internal diameter at 500°C and 17.5bar which will provide the heat for the pipes. This system will then be reversed so...
  14. E

    Engineering Thermodynamics homework help, water cooled air cooler

    I'm not looking for someone to tell me the answer, just help steer me in the right direction. I feel like I need to find the air density or air velocity at entry to proceed, but I'm unsure any help and guidance is greatly apricated!
  15. Istiak

    Calculate the volume change with gas temperature for this piston in a cylinder

    Solution attempt : Option : I am sure that my work is wrong. But, I must add solution attempt in PF that's why I just added that. How can I solve the problem?
  16. D

    I Black Hole to Other Universe: Violation of 1st Law?

    So I am a fan of astronomy, cosmology and astrophysics from a FAR. The math is way beyond my abilities but I like to just sometimes read and think about the very small parts I am able to comprehend. So my hats off to all of you that are able to fully enjoy this stuff, you're very lucky...
  17. Ebi Rogha

    B Is time a consequence of 2nd law of thermodynamics?

    I have heard from a knowledgeable physics proffessor, time exists independently and it is not a consequence of arrow of time. Could some body explain this?
  18. B

    B Exploring Relativistic Thermodynamics Experiments

    In most experiments of SR, we look at atomic and subatomic particles or the frequency of EM radiation. The Haefele-Keating experiment looked at the resonance of cesium atoms stimulated by a certain EM frequency https://en.wikipedia.org/wiki/Hafele–Keating_experiment The Ives-Stillwell...
  19. B

    Hard thermodynamics high school question from an entrance exam in India for colleges

    as the process has been given as an adiabatic one, dQ=0, further attempt is given in the attached files, but the problem is I got X=1 while the official key states it to be X=2.05, could anyone explain why
  20. Dario56

    Why Does Electrical Work Cause Changes in the Internal Energy of a System?

    If we look at system at constant temperature and volume which is galvanic cell, first law of thermodynamics states: $$ dU = dQ + dW' $$ Where W' is electrical work done by galvanic cell and Q is heat exchanged with surroundings. As far as I know electrical work is work done by electric field...
  21. bardia sepehrnia

    Engineering Average heat transfer coefficient (forced convection)

    So firstly, I don't understand if the mass flow rate is for steam or for water. If it is for water, I know I can find the heat transfer rate using equation:Q=mcdeltaT. But then I don't know how to find h (the average heat transfer coefficient) because I don't know the surface area (As). I can...
  22. Dario56

    Entropy Changes in Electrolytic/Galvanic Cell?

    One of the most fundamental equations in chemical thermodynamics states: $$ \Delta_rH_m^⦵ = \Delta_rG_m^⦵ + T \Delta_rS_m^⦵ $$ If we look at this equation in context of net chemical reaction in electrolytic or galvanic cell, it is usually interpreted as follows: Enthalpy of reaction denotes...
  23. E

    I To derive an equation of black hole thermodynamics

    This is the problem statement: We can start by writing ## (\star d \star d \xi)_a = - \nabla^b (d\xi)_{ab} = - \nabla^b \nabla_a \xi_b + \nabla^b \nabla_b \xi_a = 2\nabla^b \nabla_b \xi_a ##. Then with ##\nabla_a \nabla_b \xi_c = R_{cbad} \xi^d = -R_{bcad} \xi^d## we can contract over...
  24. mcas

    Show that a partial molar property is an intensive property

    I started by taking a derivative: $$E = \sum_{i=1}^{\alpha} (E_i^{(p)} n_i) \ \ \ | \cdot \frac{\partial}{\partial n_i}$$ $$\frac{\partial E}{\partial n_i}=\sum_{i=1}^{\alpha} [\frac{\partial E_i^{(p)}}{\partial n_i}n_i + E_i^{(p)} \frac{\partial n_i}{\partial n_i}]$$ $$\frac{\partial...
  25. DeathByKugelBlitz

    What exactly does the proposed 4th law of thermodynamics mean?

    'Every non-equilibrium state of a system or local subsystem for which entropy is well defined must be equipped with a metric in state space with respect to which the irreversible component of its time evolution is in the direction of steepest entropy ascent compatible with the conservation...
  26. P

    Thermodynamics problem (ideal gas law, kinetic theory, processes, etc.)

    It is a long problem, but it is simple to understand. I am having trouble with part A. My attempt: Pressure outside > pressure inside container. pV = constant (isothermal). At equilibrium, all gases are at atmospheric pressure. Because it is quasi-static, the pressures of both compartments are...
  27. J

    Resources for the physics of clouds

    Does anyone know of any good papers/lectures/textbooks/etc that discuss the physical and mathematical principles that explain the structure and motion of clouds? Thanks.
  28. AN630078

    Thermodynamics: Internal Energy, Heat and Work Problem

    Well, internal energy is the sum of the kinetic and potential energies of all the molecules within a given mass of a substance; this energy is associated with the random, disordered motion of the molecules. An example of internal energy is compressed gases; since gases occupy the total volume...
  29. bardia sepehrnia

    I How can a process be isentropic but not reversible or adiobatic?

    In the book for our thermodynamics, it states that a process that is internally reversible and adiabatic, has to be isentropic, but an isentropic process doesn't have to be reversible and adiabatic. I don't really understand this. I always thought isentropic and reversible mean the same thing...
  30. bardia sepehrnia

    Engineering Thermodynamics, Calculating the required mass flow

    I have solved this question and it seemed pretty easy, but I got an extremely large number for the mass flow, I had to post the question here to make sure I did it correctly. Any help will be appreciated.
  31. J

    Finding temperature change, thermodynamics first law

    So I calculated the final and initial pressures using the given eqns, ended up with the final pressure of 96629 and initial pressure of 62639. Then I used the PV=nRT eqn to calculate the final and initial temperatures. T=P*V/(n*1.5*R). I got an initial temperature of 81.79 and a final...
  32. P

    When do formulas for adiabatic processes apply?

    In this problem, the method used to solve the question is to equate pdV with change in internal energy. This implies an adiabatic process as Q = 0? (not sure about this claim) However, why is it not correct to simply apply the PV^ϒ = constant formula? Thank you.
  33. P

    Rate of heat flux from from hot gas in a pipe to water outside

    I have solved the first 2 parts. For the 3rd part, I have obtained the equation: T(x) - T0 = (T1 - T0)e^(-Φx/fc), where f = fm in the question. How do I obtain that expression for H? Thank you!
  34. L

    Thermodynamics problem -- Pressure oscillations in a jar

    I add a Figure with the problem and solution. I have difficulty with a solution to the given problem. Why ##F=-kx=Adp##, I do not understand minus sign because we are working with scalars not vectors. It is correct to say that ##\vec{F}=-kx\vec{i}##, but is not correct to say that ##F=-kx##. Can...
  35. Another

    Heat transfer in thermodynamics

    In answering questions (a.) Why heat intake in this system is ## \Delta Q_{sys} = ( \Delta Q_{hot water} + \Delta Q_{cold water} ) / 2 ## where. ##\Delta Q_{hot water} = c(T_1 - T_f) ## ##\Delta Q_{cold water} = c(T_2 - T_f) ## I think T or T_f should be between T_1 and T_2 But why is the...
  36. L

    Determine how many microstates and macrostates (Thermodynamics)

    Since this is a two-state paramagnet where N = 40, therefore the microstate is ##40^2##? But I am not sure how to proceed to count the number of macrostates? Because from what I understand of what a macrostate is, shouldn't there a specific outcome to be stated in order to determine how many...
  37. E

    Why is PV work in thermodynamics so difficult to understand?

    i can't manage to grasp the concept of PV work in thermodynamics, for example we all know that W= integral(F*dx) like here but this says that, at the end, W doesn't really depend on the gas temperature or reversible process crap at the end W is simply a constant, atmospheric pressure is...
  38. Chestermiller

    Thermodynamics: Constant Pressure Tank Heating Problem

    I found this interesting thermodynamics problem on another site. I thought PF members might find it challenging to attack. I'm not asking for help since I've already solved it. So pease feel free to present your entire solution if you desire. Chet
  39. K

    Thermodynamics: Ideal gas model

    Do particles have air in between them in the ideal gas model? I think the answer is 'no, but I am not quite sure about the explanation. Is it because in an ideal gas model, the volume of the particles is negligible? Thank you.
  40. E

    Other Textbook Recommendations for Thermodynamics

    Hello there, Can anybody recommend me a good thermodynamics textbook? I prefer the ones that have a deep or complete (if possible) discussion about the theoretical aspect of thermodynamics, and the mathematical aspect as well. Thank you
  41. L

    Thermodynamics: gas expansion formula or approximation error?

    FIRST TYPE: REVERSIBLE PROCESS At the temperature of 127 ° C, 1 L of CO2 is reversibly compressed from the pressure of 380 mmHg to that of 1 atm. Calculate the heat and labor exchanged assuming the gas is ideal. Q = L = - 34.95 J CONDUCT 380 mmHg = 0.5 atm L = P1 * V1 * ln (P1 / P2) = 0.5 * 1...
  42. R

    I Irreversible Isochoric Process in a Cycle

    Consider a reversible ideal gas cycle consisting of: 1. An isochoric heat addition, 2. An isothermal expansion to the initial pressure, and 3. An isobaric compression to the initial volume. What, if any, is the difference in net work done by the gas in the cycle if the isochoric heat addition...
  43. P

    Gas effusing through hole, working out time dependence

    Consider instead a thermally insulated container of volume V with a small hole of area A, containing a gas with molecular mass m. At time t = 0, the density is ##n_0## and temperature is ##T_0##. As gas effuses out through a small hole, both density and temperature inside the container will...
  44. A

    Looking for a good introductory book on thermodynamics

    Hi, I have been studying physics again and I was looking for a good introductory book for thermodynamics. I wanted to know if there is a book in thermodynamics that would be the equivalent to "An introduction to Mechanics" by Kleppner/Kolenkow, or "Electricity and Magnetism" by Purcell? These 2...
  45. bryanso

    Understanding the Laws of Thermodynamics as described by Feynman

    Hi, there is no other topics in my adventure in Feynman Lectures that makes me so loss in thoughts (https://www.feynmanlectures.caltech.edu/I_44.html). I seem to understand every sentence. But the whole thing is completely unintelligible. Let me start by asking one fundamental question. I am...
  46. A

    Thermodynamics of a Fire Resistant Safe

    Hi, I have been researching how to protect my card collection from the unlikely event of a house fire, however there is not enough data for me to estimate whether my set up is adequate or not. If anyone could approximate anything here without knowing all the exact variables (r-values) that...
  47. J

    Thermodynamics problem relating to Chemical Potentials

    For part (a), I used this formula where where the i's represent the substance being used and mu_i^0 represents some reference potential. However, to my knowledge this simply calculates the change in chemical potential from one state to another which is not of much help in finding the relative...
  48. fluidistic

    I About divergence, gradient and thermodynamics

    At some point, in Physics (more precisely in thermodynamics), I must take the divergence of a quantity like ##\mu \vec F##. Where ##\mu## is a scalar function of possibly many different variables such as temperature (which is also a scalar), position, and even magnetic field (a vector field)...
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