What is Equilibrium: Definition and 1000 Discussions

Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium there are no net macroscopic flows of matter or of energy, either within a system or between systems.
In a system that is in its own state of internal thermodynamic equilibrium, no macroscopic change occurs.
Systems in mutual thermodynamic equilibrium are simultaneously in mutual thermal, mechanical, chemical, and radiative equilibria. Systems can be in one kind of mutual equilibrium, though not in others. In thermodynamic equilibrium, all kinds of equilibrium hold at once and indefinitely, until disturbed by a thermodynamic operation. In a macroscopic equilibrium, perfectly or almost perfectly balanced microscopic exchanges occur; this is the physical explanation of the notion of macroscopic equilibrium.
A thermodynamic system in a state of internal thermodynamic equilibrium has a spatially uniform temperature. Its intensive properties, other than temperature, may be driven to spatial inhomogeneity by an unchanging long-range force field imposed on it by its surroundings.
In systems that are at a state of non-equilibrium there are, by contrast, net flows of matter or energy. If such changes can be triggered to occur in a system in which they are not already occurring, the system is said to be in a meta-stable equilibrium.
Though not a widely named "law," it is an axiom of thermodynamics that there exist states of thermodynamic equilibrium. The second law of thermodynamics states that when a body of material starts from an equilibrium state, in which, portions of it are held at different states by more or less permeable or impermeable partitions, and a thermodynamic operation removes or makes the partitions more permeable and it is isolated, then it spontaneously reaches its own, new state of internal thermodynamic equilibrium, and this is accompanied by an increase in the sum of the entropies of the portions.

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  1. M

    Calculating force to tip over a cabinet (static equilibrium)

    Homework Statement Homework Equations How do you solve for the force in this problem and also the coefficient of static friction and minimum force to tip the cabinet over if the point of application can be chosen anywhere on the cabinet? The Attempt at a Solution I tried setting up tables...
  2. G

    Equilibrium Climate Sensitivity

    Equilibrium Climate Sensitivity - what is the relevance of the word 'equilibrium' - why not 'climate sensitivity?' Hope you can help.
  3. B

    Thermal equilibrium and isolation

    If two objects are at the same temperature, but thermally isolated from one another, are they still considered to be in thermal equilibrium with one another?
  4. M

    Find the tension in the cable and the force the ramp exerts on the tires

    Homework Statement A 5000 kg car rests on a 32° slanted ramp attached to a trailer. Only a cable running from the trailer to the car prevents the car from rolling off the ramp (the car's transmission is in neutral and its brakes are off). Find the tension in the cable and the force that the...
  5. MathematicalPhysicist

    Equilibrium Statistics -- Euler summation formula

    Homework Statement In the calculation in high temperatures of ##Z_{rot} = (\sum_{j=0}^\infty (2j+1)\exp{j(j+1)\theta_{rot}/T})^N##; they use Euler summation formula: $$\sum_{n=0}^\infty f(n) = \int_0^\infty f(x)dx+\frac{1}{2}f(0)-\frac{1}{12}f'(0)+\frac{1}{720}f^{(3)}(0)+\ldots$$ for ##f(x) =...
  6. A

    Spring angles at static equilibrium on application of force

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  7. D

    Water molecules effect on Hydrogen bonds in precipitation

    Cheers everyone. Can the amount of water molecules added to a solution impact the formation of a salt with its ions mainly bonded through hydrogen bonds with electrostatic like behaviour? Let me give Some background to the question first: I am studying the precipitation of Phosphorous(P) as...
  8. Pushoam

    Entropy- change & the condition when a system reaches equilibrium

    Homework Statement Homework EquationsThe Attempt at a Solution I didn't understand the last part. At eqbm. ##\Delta S = 0##. This means that the RHS of the eqnn. 14.25 is 0. This doesn't mean that the following eqns. must hold true. ##(\frac 1 T_1 - \frac 1 T_2) =0,.............(1) \\...
  9. V

    I Nuclear statistical equilibrium

    Sorry, I have never found what does it mean Nuclear statistical equilibrium. It is used in any text but exact explanation nowhere. Please explain a physical meaning of it. Thank you.
  10. R

    Equilibrium Question -- Thrust versus Lift....

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  11. J

    Rotational Equilibrium Question

    Homework Statement A bar of uniform density, length L, and mass m is suspended by two ropes of tensions T1 and T2 at either extremity of the bar. The bar is tilted such that it makes an angle θ with the ropes. A mass M is resting at a distance l from T1. https://i.imgur.com/vLlAJbe.png If...
  12. Z

    Equilibrium of pistons with different radii (Hydraulics)

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  13. curiosity colour

    Chemical Equilibrium Q: How Does Solution (a) Know PH2S=Ammonia?

    I have a question about the solution (a) in this example, how does it know PH2S is the same as ammonia? is there something I've miss?
  14. S

    Work energy theorem and forces at equilibrium -- Conceptual doubt

    A pendulum of mass m and length l is suspended from the ceiling of a trolley which has a constant acceleration a. Find the maximum deflection θ of the pendulum from the vertical. When I used work energy theorem, I got θ = 2 arctan(a/g). But when I took the equilibrium position and equated the...
  15. D

    I Gibbs Energy and chemical equilibrium

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  16. M

    MHB Calculate Equilibrium Constant of 2BrCl <=> Br2 + Cl2

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  17. M

    MHB Uniform rods and disk in static equilibrium

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  18. J

    Find the tension in the cable and reactive forces at ground

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  19. D

    Equilibrium volume of two differential van der Waal gases

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  20. math4everyone

    A Equilibrium in system of non-linear difference equations

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  21. alemsalem

    A Calculating Einstein's coefficients in QFT vs equilibrium

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  22. esha

    Potential energy and equilibrium

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  23. U

    Pressure dependence of the equilibrium constant for an ideal gas

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  24. M

    2 body engine, final equilibrium temperate and work produced

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  25. E

    Basic torque/static equilibrium problem

    Homework Statement Homework Equations sum of forces = 0N sum of torque = 0Nm The Attempt at a Solution Net force has to be already zero (T = mg). But, the torque isn't zero, otherwise this question would have another answer choice. But the gravitational torque should cancel with the tension...
  26. D

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  27. Strawberry1711

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  28. B

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  29. durant35

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  30. D

    B How can anyone explain the universal equilibrium density problem

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  31. karush

    MHB -Identify the equilibrium values y'=5\sqrt{5},y>0

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  32. tom.stoer

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  33. Mateus Buarque

    Simple Harmonic Motion and equilibrium of springs

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  34. T

    Why Does Tension Vary Along the Rope in a Hanging Superhero Scenario?

    Homework Statement [/B] Superhero and Trusty Sidekick hang motionless from a rope. Superhero’s mass is 90.0 kg, while Trusty Sidekick’s is 55.0 kg, and the mass of the rope is negligible. (a) Draw a free-body diagram of the situation. (b) Find the tension in the rope above Superhero. (c)...
  35. esha

    Why is degree of ionization inversely proportional to....

    Degree of ionization is the number of particles which dissociate by the total number of particles. if that's the case then higher number of particles should mean higher number of particles which get dissociated. this should also mean higher the concentration the degree of ionization will also...
  36. person123

    Exploring Pulley System Equilibrium: Solving for y when x Changes

    I was working on a pulley system as shown here: The mass on the right and left side is equivalent, and I am solving for when the system is in static equilibrium. Theta is the angle between the rope on either side of one of the pulleys. H and y are both measured from the original position of...
  37. F

    Direction of Normal Force on Object B: A Scientific Inquiry

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  38. M

    Naive Doubt About Thermodynamic Equilibrium

    This is more of a recurring conceptual doubt that I keep on running into when solving thermodynamics problems. We are taught that variations between extensive state variables in equilibrium are given by the following 'fundamental formula': dE = TdS + \mathbf{J}\cdot{d}\mathbf{x} +...
  39. N

    How Many Moles of BaCO3 Dissolve in Water Given Kc?

    Homework Statement Excess BaCO3 is placed in a container containing 5L of pure water. Given the following info: BaCO3 (s) ↔ Ba2+ + CO3 2- and Kc = 5.7E-6 how many moles of BaCO3 dissolve? Homework Equations Kc=(Ba2+ )(CO3 2- ) = 5.7E-6 The Attempt at a Solution solved for x to get .002387...
  40. S

    Assumption of local thermodynamic equilibrium in a fluid

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  41. S

    Duration of Equilibrium Reaction

    I am wondering the answer to the following question, and what equation you would use to solve it: What is the duration of the following reversible reaction? A <--> B You have 10 moles of A and zero moles of B. After 1 minute, 25% of A turns into B, and 50% of B turns into A. My class...
  42. alex91alex91alex

    Equilibrium of Non-Uniform Box on Two Scales

    Homework Statement A non-uniform box sits on two scales as seen below. Scale A reads 10.2N, and scale B reads 19.4N. Question: How far from the left end of the box is the center of mass located? Homework Equations τccw=τcw τ=f*d(from pivot point) The Attempt at a Solution If I choose the...
  43. M

    How is "always" spontaneous reconciled with equilibrium?

    Many introductory (high school chemistry) texts speak of reactions that are “always” or “never” spontaneous (in the former case they reference reactions where ∆H is - and ∆S is +, for example). I struggle with this concept when considering reactions in closed systems. Premise: All reactions...
  44. M

    Equilibrium in a pure substance

    The book says when the water is heated, the pressure stays constant. But I do not understand pressure for a liquid-water system. What is the pressure for a liquid here? the pressure on the surface, botton or sides? Source: Fundamentals of Thermodynamics by Sonntag/Borgnakke/Van Wylen. Thank you.
  45. Redwall54

    Torque and rotational equilibrium question

    Homework Statement 8. A 20 kg uniform beam 10m long is attached to a wall with a cable. The cable is attached to the middle of the beam at a 90 degree angle to the beam. A box of mass 5 kg is also suspended from the beam. In addition to this, the beam is attached to the hinge at the bottom...
  46. E

    Ideal gas in a cylinder with a piston

    Homework Statement A vertical cylinder of radius r contains an ideal gas and is fitted with a piston of mass m that is free to move. The piston and the walls of the cylinder are frictionless, and the entire cylinder is placed in a constant-temperature bath. The outside air pressure is p0. In...
  47. T

    Effect of Temperature on Chemical Reaction Equilibrium

    here is the question (part I): For part I, I need some assistance, I cannot figure out how to do the question. I know eventually what to do, it's just working out the equilibrium constants I'm having trouble with. So to start, I want to work out the K values at 600K and 800K, I do this by...
  48. N

    How Do You Solve a Chemical Equilibrium Problem Involving AuCl, NaCl, and H2O?

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  49. A

    I Time of cooling to equilibrium in space plasma gas

    Hi all, If I have a hot object in space (not a star but say an oven or just a hot gas as would be on Earth < 10,000 degrees Kelvin) glowing at a temperature T and I want to know long it takes to come to equilibrium with the vacuum of space around it, how can I calculate such a time? I could...
  50. Louns

    Equilibrium Force on Floating Object

    Homework Statement This problem is found in The Exercises for the Feynman Lectures on Physics: A flat steel plate floating on mercury is acted upon by three forces at three corners of a square of side 0.100 m. Find a single fourth force which will hold the plate in equilibrium. Give the...
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