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. A

    Static equilibrium - man on a ladder

    Homework Statement Here's a screen shot of the problem statement: http://i.imgur.com/IRI02Ne.png For the purpose of this post, I'll label the given information as: a = left side of ladder (2.5m) a' = distance from floor to the point where the man is standing (2.0m) b = right side of ladder...
  2. R

    Forces in Equilibrium acting on wall climber

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Hello and thank you in advance for any help. I am currently studying physics and having difficulty working out a forces at equilibrium problem. With limited given variables, I am unable to see...
  3. P

    Static Equilibrium - trick question?

    Homework Statement A man stands on a board of negligible mass with a length of 10m is supported by 2 cables, one on the left on one on the right, with a tension of 300N and 200N respectively. How much does the man weigh in Newtons?Homework Equations F=ma Torque= F*lever arm The Attempt at a...
  4. B

    Equilibrium Process for Calculating Tension in a Tight-Rope Walker's Wire

    Homework Statement A 60 kg tight-rope walker carries a long beam with a mass of 30 kg across a 10 m long wire. When she is at the centre of the wire (i.e. 5 m across), each section of the wire makes an angle of 5° to the horizontal. Assuming that the mass of the wire is negligible, calculate...
  5. lonely_nucleus

    Direction of equilibrium if you remove heat from exothermic reaction

    If you remove heat from an exothermic reaction will the equilibrium shift to the products or to the reactants according to le chatelier's principle
  6. anton717

    Interesting Equilibrium Question

    Homework Statement Assume the wooden ruler is balanced and that it has uniform density. If the wood is replaced by metal, increasing the mass and density of the ruler without changing its dimensions (and remaining uniform), the ruler will... (Assume the length of the ruler is 1 meter.) Looks...
  7. K

    MHB Verification of argument for global asymptotic stability of equilibrium point

    I am working on proving that an equilibrium point of a two-dimensional dynamical system is globally asymptotically stable. The background and justifications are below. I have gotten to the final steps (in bold), but cannot justify it. It seems right intuitively. Can someone navigate the argument...
  8. D

    Find the equilibrium position of the winch

    Homework Statement A whip made from a material shaped shaft axis radius R and moment of inertia I and a crank with the axis perpendicular to the axis of rotation of length l and mass m, while the rest parallel to the handle - mass ##m_{2}##. It hangs on a hoist that has mass m. Suppose rope...
  9. G

    Gibbs free energy and equilibrium constant at a high T

    I posted this earlier, but I just realized it might have been in the wrong section. Sorry Okay, so consider you have system in which ΔG<0 and ΔS>0. Using Gibbs free energy (ΔG=ΔH-TΔS), you'll know that it will always be negative. As the temperature increases, it will actually become more and...
  10. I

    Thermodynamics equilibrium problem

    Please help me solve this... Two rigid tanks are connected by a valve. Initially, tank A contains 0.2m3 of n2 at 350k and 100Kpa. tank B contains 0.5m3 O2 at 500k and 250Kpa. The valve between the tanks is open and the two gases are allowed to mix. Assuming constant specific heats at the given...
  11. E

    Chemical equilibrium for simultaneous dissociation reactions

    Hello everyone, Sorry I didn't have the time to rewrite the question, Can you help me with this?
  12. L

    Equilibrium Question with water and ice

    Homework Statement 5.0 kg of ice at 0◦ is put into 3.0 kg of water at 20◦C. Assuming that they are isolated, that cH2O = 4186 J /kg K , and that L = 3.3 × 105 J/ kg how much ice is left when the system comes to equilibrium? Homework Equations Q= +/- mL Q=mcΔT The Attempt at a Solution...
  13. C

    Equilibrium Question: Arbitrary Axis of Rotation?

    Ok, I solved the question posed in the attached image. I did so by using the car's center of mass as the location of my axis of rotation, generated torque and force equilibrium equations, and solved for all unknowns. When I try to use another location for my axis of rotation, e.g., the point...
  14. L

    Moment of force and static equilibrium

    1) Problem: An individual holds a ball of mass 3 kg in his hand in static equilibrium. The biceps brachii attaches a distance of 2 cm from the centre of rotation of the elbow joint, and the muscle's line of action is directed at an angle of 115° counter clockwise from the forearm. The forearm...
  15. H

    Equilibrium and torque problem

    Homework Statement A uniform rod AB of length 5 m and weight 50 N is pivoted at A and held in equilibrium by a rope as shown. A load of 100 N hangs from the rod at a distance x from A. If the breaking strength of the rope is 50 N, find the maximum value of X. Homework Equations τnet =...
  16. C

    Boltzmann equation and Kinetic equilibrium

    In section 3.1 of Dodelson's "Modern Cosmology", after introducing the Boltzmann equation, in the second paragraph of page 60 the author states that: "The first, most important realization is that scattering processes typically enforce kinetic equilibrium. That is, scattering takes place so...
  17. T

    Feedback and equilibrium between black holes and galaxies

    "The supermassive black hole is sucking interstellar gas, but at the same time it is affecting the star-formation history of the galaxy with its powerful winds," Tombesi said. "Astrophysicists describe this process as a feedback between the central supermassive black hole and the galaxy, which...
  18. C

    Boltzmann equation Kinetic equilibrium (Dodelson)

    In section 3.1 of Dodelson's "Modern Cosmology", after introducing the Boltzmann equation, in the second paragraph of page 60 the author states that: "The first, most important realization is that scattering processes typically enforce kinetic equilibrium. That is, scattering takes place so...
  19. 1

    Why is there a vertical force on the pin in this static equilibrium setup?

    Q: Why does the pin have a vertical force in this diagram (Static equilibrium)? The diagram depicts as follows: A mass (M) sits a a distance (d) away from the end of a board of length L. The board has a mass of m and is held to a wall by a pin and string. The string has a tension (T) and is at...
  20. Valerie Prowse

    Equilibrium problem - Vertical beam, cable

    Homework Statement A uniform vertical beam of mass 40 kg is acted on by a horizontal force of 520 N at its top and is held, in the vertical position, by a cable as shown. a. Draw a free-body diagram for the beam, clearly labeling all of the forces acting on it. b. Calculate the tension in the...
  21. I

    Equilibrium Reactions: Not All Elementary?

    The rate law is given by R=k[A]^m[ B]^n where m,n needn't be equal to stoichiometric coefficients...but we use r=k[A]^a[ B]^b where a,b are stoichiometric coefficients when we use ratio rate of forward to rate of backward reaction in getting value of equilibrium constant K for any given reaction...
  22. kostoglotov

    Three point charges with a central fourth charge

    Homework Statement It is the last part, part (c) that I'm having trouble with, but I'll post the entire question for clarity. Three charges (q) form the vertices of an equilateral triangle. A fourth charge Q ( Q = -q ) is placed at the center of the triangle. (a) will the charges at the...
  23. M

    Center of mass vs center of support of equilibrium

    Homework Statement Where is the difference between center of support of equilibrium and center of mass of system. For example we are given a ruler with length L and mass M and two builds with mass m1 and m2 on its edges. Homework Equations http://imgur.com/PiGA817 The Attempt at a Solution I...
  24. M

    How many bricks can be put without disordering the equilibrium

    Homework Statement A homogenous brick with length L, is on a horizontal surface. On this brick are put one after another other bricks, which are the same with the first. Every brick is moved along L/5 units horizontally from the predecessor one. How many bricks can be put without disordering...
  25. J

    Expressing the equation of hydrostatic equilibrium

    Homework Statement This problem has been stumping me for days now, I'm sure I'm missing something simple as it's only worth a small number of marks on the coursework. Any help would be appreciated. I've been asked to re-express the equation of hydrostatic equilibrium: dP/dr = - Gm/4πr4...
  26. S

    Calculating Kc for A+B-->C With B=0 at Equilibrium

    If I'm trying to find the Kc for A + B --> C and we know that A is in excess, pushing the reaction to the right. At equilibrium, B is 0 essentially. My question is for calculating Kc = [C]/[A][ B ] do we use the equation Kc = [C]/[A] because [ B ]is essentially 0 at equilibrium?
  27. B

    System in static equilibrium given a nudge. What happens?

    We're given a problem: A 2.0 kg mass hangs from a rope attached to an unknown mass m on a frictionless ramp inclined at 20 degrees above the horizontal. This is drawn as a diagram which shows the incline at 20 degrees where the hanging mass is 2.0 kg and the attatched mass on the frictionless...
  28. Alettix

    Angle of Inclination of a Water Surface

    Homework Statement So the full problem is the following: "On the top of a truck, there is a cubic container with a side-lenght of 1,00 m and it's filled with 500 liters of water. The truck accelerates with 2.0 m/s2 in the x-direction during the whole experiment. When the watersurface has...
  29. R

    Exploring Equilibrium During Phase Changes: DeltaG=0 and DeltaH=TdeltaS

    I am in the section of Gibbs Energy for my chemistry course and in the textbook it says the system is at equilibrium at the boiling point, so deltaG=0, and deltaH=TdeltaS. I was just wondering if the system is always at equilibrium during any phase change, not just at its boiling point. Thanks!
  30. H

    Mass needed for static equilibrium compound pulley system

    Homework Statement For what m1 will the illustrated pulley system be in static equilibrium if m2 = 60 kg? Homework EquationsThe Attempt at a Solution im supposed to use the change in lengths but don't know how to do it
  31. Q

    Problem of fluid -- Blocks, pulley, two fluids

    Homework Statement dynamic viscosity 1 = 1125 2 kgf-s / m2 , dynamic viscosity 2 = 62.5 2 kgf-s / m2 , Areas: A1 = 20 cm2 , A2 = 50 cm2 W1 = 15 Kgf, W2 = 40 Kgf. The block (2) is displaced downwards with a constant speed of 80 mm / sec, whereas linear velocity distribution determined: 1) The...
  32. L

    Equilibrium in Two Dimensions: What Force Does a Hanging Boy Exert on Each Tree?

    Homework Statement a boy on whom the force of gravity is 400 N hangs on to the middle of a rope stretched between two trees. The rope sags in such a way that it makes an angle of 170 degrees at the boys hands. what force does the rope exert on each tree? Homework Equations F=ma The Attempt at...
  33. R

    Homework question Static Equilibrium, resultant velocity

    Homework Statement See the attached sheet, I had missed todays class due to dentist and I found out we had an assignment due today by end of day, I am having trouble learning this on my own, I am trying right now. Could anyone help me with the solutions? Homework Equations Question one is...
  34. B

    Question about static equilibrium

    Homework Statement A Ladder weighs 20 Lbs. IT rests against a smooth wall at point B. Theta=45. If you pull the ladder at its midpoint, how much force is needed to make it slide at point A? u=.6. The ladder is 15 ft long, Point b is the top and point A is the bottom. 45 Deg is the bottom angle...
  35. C

    How does a catalyst affect equilibrium?

    OK I clicked a bunch of similar discussions, but it still makes no sense, I barely know what a catalyst is, besides the fact that they do affect the rate of reaction but not the equilibrium expression or pressure, which just got me hella fudged up. And i don't want any over complicated...
  36. F

    Maxwell distribution in thermal equilibrium

    Homework Statement In thermal equilibrium, the particle in a gas are distributed in velocity space according to the Maxwell distribution f(v) = A*exp(-mv^2/(2KT)) What is the average velocity ? What is the most probable velocity ? Homework Equations <v> = ∫∫∫vf(v)d3v = (0 to infinty)...
  37. MexChemE

    Equilibrium of ammonia synthesis

    Homework Statement In order to obtain commercial conversion levels in the production of ammonia, reactors operate between a pressure range from 150 to 300 atm, and a temperature range from 700 to 750 K. Calculate the mole fraction of N2 when the reaction reaches equilibrium at 300 atm and 723...
  38. S

    Aqueous Equilibrium: Ka of an Unknown Acid via Titration

    Homework Statement We're given an unknown acid, and dissolve an unknown mass of the acid in an unknown amount of water. We then titrated the solution with an unknown molarity solution of NaOH. After titrating in 10.0 mL of NaOH, we measure a pH of 5. After 34.68 mL of NaOH, we realize we...
  39. patrickbotros

    Equilibrium Problem: Relationship Between Q, K, and ∆G

    I just took a test today, and I want to see if I got the right answer. I sort of guessed. Here's the question: Which statement is correct? a) When Q<K, then ∆G=1 b) When Q<K, then ∆G=-∆S c) When Q=K, then ∆G=0 d) When Q>K, then ∆G=1 e) When Q>K, then ∆G=-RT I put C, because when Q=K, the...
  40. patrickbotros

    When to use which Equilibrium Constant. (Kp vs. Kc)

    Hello forum! My name's Patrick, and I'm taking Chemistry 212. We're learning about equilibrium and I'm constantly getting K's confused. For example: In the equation ΔG=-RT*ln(K), I have no clue whether to use the Kp value or the Kc value. Could I have used either? I just need a very thorough...
  41. It's me

    Callen Thermodynamics 2.8-2 matter flow equilibrium

    Homework Statement A two component gaseous system has a fundamental equation of the form $$S=AU^{1/3} V^{1/3} N^{1/3} + \frac{BN_1N_2}{N}$$ where $$N=N_1+N_2$$ and A and B are positive constants. A closed cylinder of total volume 2V_0 is separated into two equal subvolumes by a rigid diathermal...
  42. X

    Why does the potential difference between two capacitors seek equilibrium?

    Suppose we have a circuit with two capacitors connected to each other, C1 and C2. C1 is charged and has a potential difference of 5 V (V1=5V), but C2 is not charged (V2=0) Apparently it is known that the potential difference of these two capacitors will want to reach equilibrium. So V1=V2...
  43. P

    Equilibrium of Beams: Understanding Forces and Reactions

    hello! I don't understand, what is the equation that we use in beams is it that forces 1,2,3 equal with the reactions at the two supporting points? or the torques are 1,2,3 equal with the reactions at the two supporting points? and how do we find the reactions at the supporting points? thanks!
  44. hdp12

    Problem Check: Equilibrium of Particles

    Homework Statement A continuous cable of total length 4 m is wrapped around the small pulleys at A, B, C, D. If each spring is stretched 300 mm, determine the mass m of each block. Neglect the weight of the pulleys and cords. The springs are unstretched when d=2 m. The Attempt at a Solution I...
  45. K

    Explanation of Iodine Equilibrium in immiscible solvents

    Homework Statement I'm studying the equilibrium of I2 and its distribution in two immiscible liquids (varsol and aqueous potassium iodide). Since I2 is non polar; it will "prefer" to be in varsol but since KI (aq) is an ionic salt solution, iodine will also dissolve to give the I3- ion. When...
  46. R

    Balancing two rollers on a hill

    Homework Statement Two rollers, of masses 2kg and 3kg, are connected over a pulley by a massless string. They rest in equilibrium on two inclined slopes, as shown in the diagram to the left. Friction is negligible. What is the distance X? Homework Equations Fg = mg Component of Fg parallel to...
  47. S

    Shielding simulation and nuclide vector

    I have to make a shielding calculation of some radioactive scrap metal in a cask, using Geant4 (hence Monte-Carlo). I will be given a nuclide vector and I'll have to calculate the ambient dose equivalent rate outside of the cask. The nuclide vector I will be given will be something like: Co60...
  48. A

    Pressure/Temperature mechanical equilibrium

    1. Homework Statement Three thermally insulated containers of equal volume are connected together by thin tubes of negligible volume so that gas can flow from one container to the next when a valve between them is open. Initially, the pressure and temperature in each container is at the same...
  49. B

    Equilibrium expressions and partial pressures

    Homework Statement In considering the reaction: 3NO (g) + H2O (l) → 2HNO3 (aq) + NO (g) student A writes the equilibrium expression as: K=[NO][HNO3]2/[NO2]3 while student B writes: K=PNO [HNO3]2/[NO2]3 Whose equation is correct? Homework Equations NA The Attempt at a Solution This is a...
  50. B

    Is the System at Equilibrium with Given Concentrations?

    Homework Statement Consider the following reaction: H2 + I2 → 2HI (all gases) At 740 K, this reaction has an equilibrium constant of 50. If, at 740 K, the concentration of hydrogen gas is 2 M, iodine gas is 3 M, and hydrogen iodide gas is 6 M: (A) the concentration of hydrogen iodide will...
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