Equilibrium Definition and 1000 Threads

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. C

    Chemical potential equilibrium cosmology

    In Dodelson's "Introduction to Modern Cosmology" at p. 61 he introduces a non- equilibrium number density $$n_i = g_i e^{\mu_i/T} \int \frac{d^3p}{(2\pi)^3} e^{-E_i/T}$$ and an equilibrium number density $$n_i^{(0)} = g_i \int \frac{d^3p}{(2\pi)^3} e^{-E_i/T},$$ from which it follows that the...
  2. Sivaraman

    Homogeneous equilibrium model-fluid flow

    Hello,I am trying to calculate the velocity in a pipe with length L and Dia D, which is connected to bottom of a pressurized vessel (Vessel dimensions are known, Level of liquid inside the vessel is known). Now i need to figure out the velocity as a function of pressure inside the vessel.We can...
  3. M

    Equilibrium of Charges on a Square: Find q

    four charges each equal -Q placed at the four edges of a square and a charge q is placed at the centre. if system is in equilibrium the value of q is, the answer is q = Q/4 * ( 1 + 2(√2) can anyone please solve this, would be great
  4. M

    Rotational equilibrium equation - Moment of Forces (2D prob)

    Homework Statement The landing gear of an aircraft is composed of a main leg OA (with a weight including the wheel is 1000N to G) and two secondary links BC and 50cm long each CD. The DC link forms an angle θ of 30 degrees with the vertical. a) Add the rotational equilibrium equation with...
  5. GM Jackson

    How does a black body emit as much energy as it absorbs?

    Homework Statement A black body absorbs all incident electromagnetic radiation, including visible light which has wavelengths from 380nm to 750nm. IR radiation has wavelengths that are so long they are measured in microns. That suggests that visible light has a higher frequency than IR, and...
  6. Aravind Raj

    Physical meaning of equations of equilibrium

    From the equations of equilibrium "σy+(∂σy/∂y)*(lower case delta y)" is the force acting along y direction. can anybody explain the physical meaning of the second part of the force where we multiply delta and del?
  7. D

    How Does Adding Water Affect the Equilibrium in the BiOCl Dissolution Reaction?

    Hey everyone, At the moment I am stuck with an example and was wondering if someone could please explain it to me: You have the equation: BiOCl(s) + 2H+(aq) -><- Bi3+(aq) +Cl-(aq) +H2O(l) Why is it that when you add extra water to the system, there is no change to the equilibrium? I would...
  8. Curieuse

    How Much Force is Needed to Lift a Wheel Over an Obstacle?

    1. Problem statement In figure, what magnitude of (constant) force F applied horizontally at the axle of the wheel is necessary to raise the wheel over an obstacle of height h=3.00cm ? The wheel's radius is r=6.00cm , and it's mass is m=0.800 kg. Homework Equations Balance of forces: Fnet=0...
  9. goonking

    Solving for Equilibrium: Water vs Mercury

    Homework Statement Homework Equations P1= Patm + ρwatervg P2= Patm + ρmer.vg The Attempt at a Solution so both sides of the tubes are open to atmosphere pressure and are in equilibrium. I can get P1 =P2 the 1 atm from each side cancels out. g (gravity) cancels out I'm left with volume (or...
  10. K

    Are two charges always in electrostatic equilibrium?

    What I studied was that the force on one charge due to another equal charge in the system of two charges was, (say) F; whereas the force on the other charge due to the first charge was found out to be -F. Hence they add up to be zero. So can I say that the two equal charges are in electrostatic...
  11. 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...
  12. 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...
  13. 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...
  14. 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...
  15. 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
  16. 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...
  17. 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...
  18. 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...
  19. 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...
  20. 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...
  21. 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?
  22. 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...
  23. 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...
  24. 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...
  25. H

    What is the Maximum Distance for the Load on the Rod?

    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 =...
  26. 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...
  27. 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...
  28. 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...
  29. 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...
  30. 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...
  31. 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...
  32. 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...
  33. 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...
  34. 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...
  35. 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...
  36. 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?
  37. 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...
  38. 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...
  39. 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!
  40. 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
  41. 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...
  42. 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...
  43. 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...
  44. 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...
  45. 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...
  46. 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)...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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