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. 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...
  2. 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...
  3. 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...
  4. 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.
  5. 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...
  6. E

    Ideal gas in a cylinder with a piston

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  7. 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...
  8. N

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

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  9. 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...
  10. 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...
  11. A

    B Will there be a reaction at the hinge B in this question?

    I have solved this question by completely disregarding the reaction at the hinge B. And surprisingly, answer turns out to be correct. Why is that so?
  12. Ned Taylor

    Difference between products and reactants? Equilibrium

    Homework Statement Given the reaction, at equilibrium, it was found that [C] = 0.20 mol/L, [D] = 0.55 mol/L, [A] = 0.30 mol/L and [ B] = 0.48 mol/L. Calculate the value of Keq. Reaction: C + D <--> A + B Homework Equations K=products/reactants The Attempt at a Solution [/B] If we assume that...
  13. K

    MHB How to Calculate Equilibrium Price with Given Information?

    I do not understand how to calculate the equilibrium price of an object. Say i have the following information how would i set up the information to solve for the price? Price of (Insert the name of your good or service) Quantity Demanded Quantity Supplied (in this order.) \$7.99, 35, 21...
  14. Vitani11

    Difference b/t equilibrium and unstretched length of spring?

    Homework Statement Consider a mass attached to four identical springs, as shown in the figure. Each spring has a force constant k and an unstretched length lo, and the length of each spring when the mass is at equilibrium at the origin is a (not necessarily the same as lo). When the mass is...
  15. digogalvao

    Leidenfrost effect at thermodynamic equilibrium

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  16. E

    Why Isn't the Sum of Torques Zero in This Ladder Equilibrium Problem?

    Homework Statement Two ladders, 4.00 m and 3.00 m long, are hinged at point A and tied together by a horizontal rope 0.90 m above the floor (Fig. P11.89). The ladders weigh 480 N and 360 N, respectively, and the center of gravity of each is at its center. Assume that the floor is freshly waxed...
  17. E

    I Hall Effect: Electric Field Direction at Equilibrium

    I have a good understanding on the hall effect. However, I was told by my tutor that the electric field direction at equilibrium remains pointing in the negative side of the conducting material and the force it generated is canceled out. But further reading online text, the electric field...
  18. haushofer

    I Inflation, horizon-problem and thermal equilibrium

    Dear all, for the topic https://www.physicsforums.com/threads/problems-with-the-theory-of-inflation.905230/ I came across the following paper: https://arxiv.org/abs/1505.01456. In this paper the following arguments are given why the horizon problem is a fake problem. It raised by me the...
  19. Buzz Bloom

    I Q re equilibrium energy relationships for a mixture

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  20. H

    Calculating Forces and Equilibrium of a Drawbridge

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  21. karush

    MHB 9.4.5 Identify the equilibrium values

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  22. AdrianMachin

    Finding third charge coordinates in an equilibrium position

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  23. F

    Why is the friction force at A not considered in forces in equilibrium?

    Homework Statement [moderator note: Post edited to make problem statement images visible] https://www.physicsforums.com/attachments/question-jpg.113056/ My question is when forces are resolved horizontally, why is the friction force at A not taken into account? The Attempt at a Solution...
  24. J

    Static Equilibrium: Understanding Changes in Tension and Vertical Force

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  25. Kevin de Oliveira

    Static Equilibrium: Why Does Changing Pulley Position Affect Relative Angles?

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  26. R

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  27. L

    Fermi energy for two spin states equal in equilibrium?

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  28. C

    Equilibrium Temperature with three substances

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  29. G

    What is the equilibrium temperature of a collector plate?

    Homework Statement You would like to put a solar hot water system on your roof, but you're not sure it's feasible. A reference book on solar energy shows that the ground-level solar intensity in your city is 750 W/m^2 for at least 5 hours a day throughout most of the year. Assuming that a...
  30. Nogniks

    I NMR: RF-pulse response away from equilibrium

    Hello everybody, I've got a gap in my understanding regarding NMR systems, and I hope you can help: if the magnetisation of a proton is M0 in the Mz direction initially, a 90ox-RF-pulse will change the magnetisation to M0 in the My direction immediately after the pulse. But what happens when a...
  31. ElPimiento

    Equilibrium temperature of some ice and steam

    Homework Statement "A well-insulated bucket of negligible heat capacity contains 120 g of ice at 0°C. If 20 g of steam at 100°C is injected into the bucket, what is the final equilibrium temperature of the system?" Homework Equations $$Q_{fus} = m_{water}L_{fus}$$ $$Q_{vap} =...
  32. nickyfernandezzz

    How does friction act between PA and AB in an equilibrium of forces system?

    Homework Statement The original question was to find the value of the angle between PA and AB. I have a certain idea regarding how to find it, but first I have to identify all forces acting on the system and their directions. So, I would be grateful if someone can explain how the frictional...
  33. B

    [Equilibrium] Max of A in Saturated Solution B

    Homework Statement What is the maximum [CO32-] that can exist in a saturated solution of AgBr? Homework Equations Equilibrium Constants, ICE tables sqrt = square root The Attempt at a Solution Ksp = [Ag+][Br-] sqrt(5.4E-13) = x (Ag and Br are in equal proportion to one another) where x...
  34. A

    Efficient way to solve truss by hand

    Homework Statement Hello. Given the statically determinate truss shown in the image, solve for all forces in the members, in terms of the load P. Homework Equations Equations of equilibrium. Node analysis. Section analysis. The Attempt at a Solution I was able to solve it by solving first...
  35. AliSkully

    Help with understanding equilibrium & temperature

    Can someone explain why when you increase the temperature on an endothermic reaction, it yields more products? Is it because the activation energy is higher in an endothermic reaction, so there is more time for the products to form? also why does decreasing the temperature yield more products in...
  36. W

    Equations for Normal Forces at A and B: F_A + F_B = 0d * F_A - b * F_B = 0

    1. Homework Statement This isn't really a problem but an example in an online lecture. I'm trying to understand everything for when I get to harder questions but am having trouble understanding the "d/b" part of the equation. Homework Equations How does dividing d by b help solve for the...
  37. Aleph_null

    Find the minimum and maximum of a ratio for equilibrium

    Homework Statement Consider the rod as shown in the figure. The coefficient of static friction at A and B is \mu_s. I'm trying to find how big and how small the ratio l/d can be for the rod to still be in equilibrium. I have calculated how big all forces are acting upon the rod in the case...
  38. V

    Acid-Base Equilib: Solving Homework Problem

    Homework Statement To unclog a drain you add 26g of sodium hydroxide to 150mL of water. Calculate the pH and pOH for the solution you prepared. Can someone tell me if I'm doing it right. Homework EquationsThe Attempt at a Solution n = m/M n = 26/40 n = 0.65mol for 0.15L Does this mean that I...
  39. V

    What Happens to Copper (II) Chloride Solution Under Different Conditions?

    Homework Statement For this experiment we studied the equilibrium system CuCl42+(aq) ↔ Cu2+ + 4Cl-(aq) + heat Net reaction shift is observed by looking at colour changes -CuCl42+(aq) become green (shift to left) - Cu2+ is blue and Cl-(aq) is colourless (shift to right) What occurs when you put...
  40. B

    Effect of an Inert Gas on Equilibrium

    Homework Statement N2O4(g) + energy <---> 2NO2(g) How are Keq and [N2O4] affected by the addition of Ne, an inert gas, in a container at constant volume and temperature. Keq [N2O4] a) no change/no change b) no change/ increases c) increases/decreases d) decreases/increases Homework...
  41. L

    How high does a pendulum go after pushing at equilibrium?

    Usually, the pendulum problems I encounter relate to initial velocity. What happens if, at equilibrium, I push a pendulum with a certain amount of force? (E.g. 10N) Is there a way to calculate how high the pendulum will go? I guess it's complicated considering torque done by gravity, etc
  42. C

    Equilibrium pressure of calcium carbonate

    Homework Statement Calcium carbonate primarily occurs as two crystalline forms, calcite and aragonite. The value of∆!° for the transition CaCO3(calcite) ⇌ CaCO3(aragonite) is +1.04 kJ·mol-1 at 25°C. At that temperature the density for calcite is 2.710 g·cm-3, and that of aragonite is 2.930...
  43. runningman19

    Vapor-Liquid Equilibrium Calculations

    Hi Everyone, I am having trouble grasping the concept of Raoult's law, partial pressures etc. One problem in specific is: A system contains 3 moles of methanol and 7 moles of water at 25 degrees celsius. The temperature is raised until there is 40 mol% methanol in the gas phase. How much is...
  44. S

    A Lattice Boltzmann simulation with arbitrary equilibrium func

    Hi everyone, I plan to do a simulation of a Boltzmann equation with experimentally known scattering between two particles. Initially I intend to incorporate the scattering into the collision integral and use Lattice Boltzmann Equation (LBE) afterwards. But I only see LGBK (DnQb) which requires...
  45. B

    What is the [A2+] at Equilibrium When Mixed with B-?

    Homework Statement Equal Volumes of 3.60 M A2+ and 6.80 M B- are mixed. After the reaction, equilibrium is established with [B-] = 0.40 M. What is the [A2+] at equilibrium? Homework Equations Ice table, algebra The Attempt at a Solution This is probably a really easy problem, but I seem to be...
  46. C

    Equilibrium Calculation for Fe3O4-CO Reaction at 600°C and 5.00 atm

    Homework Statement The Reaction Fe3O4(s) + CO(g) ↔ 3 FeO(s) + CO2(g) took place at 600°C and at a constant total pressure of 5.00 atm. Determine the amount of each substance at equilibrium if there were 1 mole of Fe3O4, 2 moles of CO, .5 moles of FeO, and .3 moles of CO2...
  47. G

    I Universe thermodynamic equilibrium & Transactional Interpretation

    Hello, for those who don't know me I'm layman with some knowledge at popular science level. Discussing with a friend we came to the following point and I would like to ask it here because we had doubts about our reasoning. Cramer's Transactional Interpretation proposes that, in a sense, a...
  48. P

    What is the equilibrium force exerted by the muscle in holding a ball?

    Homework Statement A human holds a ball of mass 8kg at his hand, so that the forearm is perpendicular to the upperarm. The distance between the elbow and the center of mass of the forearm is 0.15 meters, the distance between the elbow and the muscle is 0.05 meters and the mass of the forearm...
  49. AntonPannekoek

    Find angle for the ring to be in equilibrium

    Homework Statement Find the angle Theta so that the system is in equilibrium Mass of each block: 2 Kg Mass of ring: 4π Kg Homework Equations Static equilibrium: Rotational equilibrium The Attempt at a Solution Static equilibrium: 2g + 2g + 4πg = Normal N = 4g + 4πg Taking...
  50. A

    Two monatomic ideal gases are in thermal equilibrium with ea

    Homework Statement Two monatomic ideal gases are in thermal equilibrium with each other. Gas A is composed of molecules with mass m while gas B is composed of molecules with mass 4m. The ratio of the average translational kinetic energies KA/KB is: Homework Equations KE=0.5xmxVavarage^2...
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