What is Thermodynamic: Definition and 499 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. U

    Partial differentiation: thermodynamic relations

    Homework Statement This question is about entropy of magnetic salts. I got up to the point of finding H1, the final applied field. The Attempt at a Solution But instead of doing integration I used this: dS = (∂S/∂H)*dH = (M0/4α)(ln 4)2 I removed the negative...
  2. N

    Equivalence of Canonical and Microcanonical Ensembles in Thermodynamic Limit

    In a lot of practical situations it is simply assumed the canonical and microcanonical ensemble give the same predictions, and that's fine, but I'm interested in a more exact statement of when they are indeed equivalent (in the thermodynamic limit). First of all, a thermodynamic limit must...
  3. L

    Thermodynamic cycles applied to gas turbines

    This is about the basic thermodynamic cycle of the gas turbine (i.e. Brayton or Joule cycle), consisting of adiabatic compression, heat addition at constant pressure, adiabatic expansion, and heat rejection at constant pressure, and the standard ways of analysing this through Pressure-Volume...
  4. N

    When is the fundamental thermodynamic relation true?

    dE = TdS - PdV, or equivalently \Delta E = \int T \mathrm d S - \int P \mathrm d V In general this is said to be derivable in the reversible case, however since S and V are state variables, it's also true for the irreversible case. But it can't be true for any irreversible case, since the...
  5. A

    Fundamental thermodynamic relation confusion.

    dE = dQ + dW = dQrev + dWrev = dQirev + dWirev. We have for an reversible process, dQrev = TdS and dWrev = -PdV. So; dE = TdS - PdV So this relation is for all changes (irreversible or reversible) since dS and dV are state functions. What doesn't make sense to me is the next part when...
  6. J

    Gas turbine brayton cycle thermodynamic mass flow rate of air

    Homework Statement a gas turbine is designed to produce 3000hp when using air at a maximum inlet temperature of 650k and assuming a heat loss of 70 kj/s. if the exhaust temperature is desired to be no greater than 200 degrees celsius, determine the mass flow rate of air required. Homework...
  7. M

    Question about Quantum + Thermodynamic Perturbation theory

    The following comes from Landau's Statistical Physics, chapter 32. Using a Hamiltonian \hat{H} = \hat{H}_0 + \hat{V} we get the following expression for the energy levels of a perturbed system, up to second order: E_n = E_0^{(0)} + V_{nn} + \sideset{}{'}{\sum}_m \frac{\lvert...
  8. M

    Taylor expansion of an integral (for Thermodynamic Perturbations)

    In thermodynamic perturbation theory (chapter 32 in Landau's Statistical Physics) for the Gibbs (= canonical) distribution, we have E = E_0 + V, where V is the perturbation of our energy. When we want to calculate the free energy, we have: e^{-F/T} = \int e^{-(E+V)/T} \mathrm{d}\Gamma We can...
  9. D

    Chemical diffusion derivation from thermodynamic factor and self-diffusion

    I am working through a paper in which the chemical diffusion coefficient is related to the self-diffusion (or tracer) through the following derivation, on which I am a little hung up. AB2 metal. Overall diffusion D= XADB+XBDA meaning the chemical diffusion of B is...
  10. B

    Thermodynamic energy of vibration

    I have read that every body possesses some energy of vibration due to the thermodynamic character and it is equal to 1/2 kT. Does this mean that we can detect the vibrations of bodies? Or ,as it is, does it ultimately end up as heat? Regards, Boltzmann2012
  11. T

    Understanding the Boiling Point: Thermodynamic Proof

    If we add a small amount of heat δq to a liquid at its boiling point Tb, it could either increase its temperature a small amount dT = δq/Cv, or suffer a phase change into vapor. Experimentally, we see that liquids remain at Tb until the phase change is complete, and only then continue...
  12. M

    A thermodynamic inequality (from minimum work)

    EDIT: Turns out, the solution to my question is related to the determinant of a positive definite quadratic form. This is more or less straight from Landau's Statistical Physics Part 1 (3rd edition), Chapter 21. I don't understand how the inequality/condition (the last equation in this post)...
  13. V

    Intuitive statistical mechanical explanation for thermodynamic 2nd law

    I don't have the intuitive picture of thermodynamic 2nd law, in terms of statistical mechanics. That is, why should the number of microstates be maximized in equilibrium? Anyone gives an intuitive explanation? Thanks a lot.
  14. A

    Misunderstood Thermodynamic question

    Homework Statement Plot cp as a function of temperature for O2? How does this compare with the cp expected for a diatomic ideal gas. Add this constant value to your plot. At what temperatures does the real value of cp approach that expected for a diatomic ideal gas. Homework Equations...
  15. T

    Thermodynamic equipartition of energy theorem - application to life

    hi, I'm simulating a system of molecules (water) and in order to pass through a barrier they have to overcome an energy barrier of 4kT. What is the probability of a water molecule passing the barrier or perhaps what is the average energy of a water molecule in my system? I know it's 1/2 *kT...
  16. C

    Describe the thermodynamic system of a wire.

    Homework Statement http://i.imgur.com/2WKCR.jpg Homework Equations Potentially: L(final) = L[1 + tau/(YA) + alpha(T - To)] The Attempt at a Solution Frankly I have no idea where to begin.
  17. A

    Why Can Energy and Volume Changes Be Considered Separately in Thermodynamics?

    dU = TdS - P dV Is in my book derived by viewing a proces of changing volume and energy in two separate steps. First you add energy with volume fixed, then change the volume. I'm just not sure that I understand why, you are allowed to do this. I know the changes are infinitesimal but why is...
  18. P

    Thermodynamic heat power problem

    Homework Statement Carpet steamer marketed for Greenland. Add up to 2 kg of snow or ice (no colder than -10°C) that will be converted to steam within 5 minutes. How powerful would the steamer need to be to make this claim? Know that 2108 J/kg K; Hf= 3.24*10^5 J/kg; Cwater= 4184 J/kg K; Hv =...
  19. H

    Thermodynamic- Internal energy of dry air

    Homework Statement a) what is the density of dry air when the surface pressure is 1010hPa and the temperature is 27°C. b) what is the internal energy of 1kg of dry air under these conditions? Homework Equations P=p*R*T where P is pressure and p is density. The Attempt at a...
  20. K

    Catalyst work in thermodynamic way

    What the relationship between catalyst and thermodynamic. In activation energy as we know, it reduces the activation energy and what about thermodynamic way?
  21. J

    Statistical and thermodynamic defintion of entropy

    How are both statistical and thermodynamic defintion of entropy equivalent? THe statistical definition i.e. S = k ln ω amkes sense to me. It is the number of mcirostates an atom/moelcule can take over but how is the thermodynamic definition i.e. ΔS = q/T equivalent to it...
  22. TrickyDicky

    Hydrogen and Helium-4 in thermodynamic equilibrium

    In thermodynamical equilibrium what would be the proportion of hydrogen to helium-4? According to the proton-proton chain branch I it would seem that the equilibrium would be 75% H-25% He-4? is this correct? (This is of course an unrealistic scenario).
  23. J

    Finding Qdot for a Thermodynamic Rankine Cycle

    Homework Statement Water is the working fluid in a Rankine cycle. Superheated vapor enters the turbine at 10 MPa, 480 °C condenser pressure = 6 kPa ηturbine = 80% ηpump = 70% determine a.) Qdot of the steam generator. b.) ηth c.) Qdot from the condenser to the cooling water. Homework...
  24. P

    Thermodynamic with inelastic collision

    Homework Statement [/B]A bullet traveling at 100 m/s strikes the wall inelastically. It is observed that the bullet's temperature rises by 10 Kelvin due to the collision. Find the specific heat capacity of the bullet if all of the bullet's energy goes into heat. Homework Equations ΔQ=mcΔT...
  25. H

    Thermodynamic: Conservation of Energy Question

    Homework Statement The mixing tank shown here initially contains 50 kg of water at 25°C. Suddenly the two valves and the single outlet valve are opened so that two water streams, each with a flow rate of 5 kg/min, flow into the tank, and a single exit stream with a flow rate of 10 kg/min...
  26. X

    Ideal gases thermodynamic enthelpy and internal energy change

    Homework Statement See attachment ecxample001. Homework Equations See attachment D11. The Attempt at a Solution In the first equation (Cp/R = a+bT+cT^2...etc.), Cp/R is the constant pressure specific heat. The general formula for enthalpy change is h2-h1 = integral[Cp]dT, so does...
  27. M

    Calculating Power and Efficiency of a Heat Engine with 6 kg/h Gasoline Input

    A heat Engine receives 6 kg/h gasoline which has a calorific value of 42000 kj/kg. If heat rejected from the engine is 40 kw, calculate a- the power done by the engine b- the engine effiecincy -this wt i got today in my exam and unfortuntely i didnt study it well but i did the following ...
  28. T

    Gibbs and Helmholtz equations for thermodynamic processes

    For a thermodynamic process, what equations would be used to find the change in Gibbs and Helmholtz free energy when: a.)The process is adiabatic b.)The process is isothermic c.)The process is at constant volume d.)The process is at constant pressure I know ΔG=ΔH-TΔS and ΔA=ΔU-TΔS but do...
  29. T

    Thermodynamic derivation of heat capacity

    Homework Statement cp=cv+TV?^2/? Homework Equations cp=T/N(\partialS/\partialT)p The Attempt at a Solution I have the equation, just not sure how to apply it? Any help would be appreciated
  30. R

    Thermodynamic equilibrium constants calculating the reaction free energy

    Can someone please help me answer this question and explain the concepts/solution step by step: Prof. W.H Bogus claims that he has prepared a powerful new catalyst that makes it possible to synthesize NH3 with a 70% yield in a reactor operating 500K and 2 atm pressure and having a feed...
  31. F

    Calculating work done in a thermodynamic process

    Homework Statement The figure shows a thermodynamic process followed by 130 mg of helium. How much work is done on the gas during each of the three segments? p_1 = 1.08 atm, p_2 = 5.41 atm, p_3=1.08 atm T_1=133 C, T_2=T_3=1760 C V_1=V_2=1000 cm^3, V_3=5000 cm^3 These are answers...
  32. J

    What is the Definition of Kp in the JANAF Thermodynamic Tables?

    Hi everyone, I'm learning equilibrium thermodynamics on my own. I'm wondering how is the Kp(equilibrium constants) in the JANAF tables defined? Which reaction formula does it refer to? Thanks in advance.
  33. O

    Does THERMODYNAMIC process affect phase transition in solid state metals

    I was reading an article about phase transition, i read about thermodynamic process such as Adiabatic process - a process with no heat transfer into or out of the system. Isochoric process - a process with no change in volume, in which case the system does no work. Isobaric process - a...
  34. Q

    Physics problem Thermodynamic cycle

    Homework Statement A mole of ideal gas with a temperature T1=300K is expanded isobarically until its volume is tripled .Then the gas gets colder isochorically until we reach the temperature we had in the beginning 300 K.Find the work of the gas. Hint : We have a thermodynamic cycle . Homework...
  35. A

    Thermodynamic Steam Generator Problem.

    Homework Statement I have a problem which I will attach a picture of, regarding a system composing of a heat recovery steam generator and a turbine. I have to work out the power output of the turbine, which I think I will be fine with. What I would like to know is, how does the combustion...
  36. I

    Thermodynamic - Work done in a system

    Homework Statement The question is as following: One litre of an ideal gas, initially at atmospheric pressure, is held at a constant temperature of 300 K (by maintaining good thermal contact with a thermal reservoir held at this temperature). The volume is decreased until the pressure doubles...
  37. J

    Development of a thermodynamic property database hydrocarbons

    Hiya guys, I've just started a project, of which the aim is to develop a thermodynamic property database for hydrcarbon fuels. I've been asked to start by reading up on the maxwell relationships and clapeyron equation etc. so hopefully this will give you an idea of what I am trying to...
  38. I

    Thermodynamic cycle related problem

    Homework Statement The problem is as following: Homework Equations \Delta E = \Delta Q-\Delta W The Attempt at a Solution Now I know that if work is done by the system then work sign is negative and that if volume remains unchanged then no work is done. Am I right to say that Internal...
  39. F

    How to derive Thermodynamic Relations from Volume Data

    I'm struggling to derive some thermodynamic equations from this http://my.safaribooksonline.com/book/chemical-engineering/9780132441902/thermodynamic-properties-from-volumetric-data/ch03lev1sec1" : Homework Statement I'm trying to derive all the equations from 3.8 to 3.14 for Pressure...
  40. M

    Thermodynamic derivation involving heat capacities

    I have the answer to this question but I'm finding it hard making sense of it... Q5) Dervive a relationship relating Cp-Cv to the isothermal compressibility (∂p/∂V)T and the coefficient of thermal expansion (∂V/∂T)p. Hint: consider the intensive entropy S as a function of T and V. So I've...
  41. A

    Thermodynamic simple conceptual question

    In an isobaric expansion process, the pressure of the gas is kept constant. Because of the increase in volume the constant pressure can only be archived by increasing temperature. Then I want to ask is the pressure of the gas necessarily equal to the external pressure throughout the whole...
  42. M

    Finding work done, heat in, and heat out over a reversible thermodynamic cycle

    1. Statement of the Problem One mole of a monatomic ideal gas is taken through the reversible cycle shown. Process bc is an adiabatic expansion, with P_b = 10.0 atm and V_b = 1.00E-3 m^3. Find a) the energy added to the gas as heat, b) the energy leaving the gas as heat, c) the net work done by...
  43. L

    Thermodynamic question involving work

    Homework Statement Show that the work done by a reversible function from P1V1 to P2V2 is W = (P1V1 -P2V2)/ (x - 1) using the relation PVx = C where X and C are constants Homework Equations dW = PdV The Attempt at a Solution I'm going to have to update this more when i get...
  44. O

    Fundamental Equation Thermodynamic Postulates

    Homework Statement Consider the fundamental equation S = AUnVmNr where A is a positive constant. Evaluate the permissible values of the three constants n, m, and r if the fundamental equation is to satisfy the thermodynamic postulates and if, in addition, we wish to have P increase with U/V...
  45. J

    Observing Thermodynamic Phase Transitions Via Neutron Scattering

    Hi, before I start this is not coursework or any work attached to my degree but part of an internship at a neutron research facility at a level appropriate for Masters students and higer, so I felt it necessary to post it here rather than the homework section (sorry if I'm mistaken). I've been...
  46. I

    Thermodynamic entropy of system of any size.

    After a bit of calculation, I came up with the following quantity for the bit-entropy of a thermodynamic system. We have the following assumptions: 1. System at thermal equilibrium. 2. Ideal gas. 3. Monatomic gas (i.e. no internal degrees of freedom for particles). 4. All particles have equal...
  47. H

    Thermodynamic processes: probably easy question

    Homework Statement I'm probably over thinking this question. An ideal gas is placed in a thin walled aluminum cylinder and slowly compressed to 25% of its original volume. The process is best described as adiabatic, isothermal, isochoric, or isobaric? Homework Equations none The...
  48. J

    Thermodynamic Ethanol Saturation

    I am doing a project and this is a problem were are having: We are trying to calibrate a MQ-3 sensor with an arduino uno board, however we have to do a hand calculation to arrive at the theoretical ethanol content (amount of ethanol saturated in the air) before we can calibrate the sensor...
  49. J

    Thermodynamic Ethanol Saturation

    I am try to calibrate an MQ-3 sensor with and Arduino board. However, I need a little help with thermodynamics, I am using a container of alcohol which has a volume of 591.470 mL, only 100mL is filled with 100 proof (50%) alcohol. However I need to calibrate the sensor to the content of...
  50. M

    Deriving thermodynamic relations

    1. The problem statement: Show that a) (∂H/∂T)V = CV(1 - βμ/κ) b) (∂H/∂V)T = μCP/Vκ c) (∂T/∂V)H = μ/(V(μβ - κ))2. Homework Equations : i) β = (1/V)(∂V/∂T)P ii) κ = -(1/V)(∂V/∂P)T iii) β/κ = (∂P/∂T)V iv) CV = (∂U/∂T)V v) CP = (∂H/∂T)P vi) CP - CV = TVβ2/κ vii) η = (∂T/∂V)U = (1/CV)(P -...
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