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.

View More On Wikipedia.org
Recent contents Top users
  1. E

    Find the Equilibrium temperature distribution of a PDE

    Homework Statement 1) What is the Equilibrium temperature distributions if α > 0? 2) Assume α > 0, k=1, and L=1, solve the PDE with initial condition u(x,0) = x(1-x) Homework Equations du/dt = k(d^2u/dx^2) - (α*u) The Attempt at a Solution I got u(x) = [(α*u*x)/2k]*[x-L] for...
  2. A

    Equilibrium Constant Calculation

    Homework Statement With the 5 equations, the equilibrium contants can be calculated at the bottom. (See image) My complication I am aware that X = 200 thus that value remains at that. Also, From the fourth equation K_{out} = Cl_{out}. But, I cannot seem to work out the values. If not...
  3. A

    Archived The drift and diffusion currents under equilibrium

    Can you help me explain this part from my book? In equilibrium, the pn junction has no external connections, i.e., the terminals are open and no voltage is applied across the device. If so, I wonder why there is drift current in the equation above. In equilibrium, the total current is zero...
  4. A

    Electric field inside PN junction in equilibrium

    I need help to understand this solution: Why electric field is zero at x < - b? I think it should be non-zero because the electric field from positive and negative ions don't completely cancel each other. How can you know E rises as x approaches zero?
  5. H

    Heat gained and lost by aluminium and water in thermal equilibrium

    Homework Statement A physicist pours 100g of water at 100'C into a 20g aluminium cup which already contains 50g of water at 20'C. The final equilibrium temperature of the water is 71.847. C(water)=4186J/kgC C(aluminium)=900J/kgC 1. the amount of heat lost by the hot water 2. the amount...
  6. marellasunny

    Equilibrium reaction ICE method to ideal gas law

    QUESTION: Say I have the following equilibrium reaction CO+\frac{1}{2}O_2\leftrightharpoons CO_2 The stoichiometric mixture of CO and $O_2$ in a closed vessel, initially at 1 atm and 300K, is exploded. Calculate the composition of the products of combustion at 2500K and the gas pressure. Take...
  7. P

    L-J Potential-Distance of equilibrium

    LJ-Potential Homework Statement Find distance of equilibrium for: 1. Uvdw(r)=-A/r6+B/r12 A=10-77 Jm6 B=10-134 Jm12 Homework Equations Uvdw(r)=-A/r6+B/r12 The Attempt at a Solution It is suppose that r is the distance, but I have not any idea how to calculate this...
  8. marellasunny

    Chemical equilibrium reaction for burned gases in engine

    I do not understand how equation(3) occurs.(taken from the book Internal Combustion Engines by John B.Heywood) $$ $$ Consider a reactive mixture of ideal gases. The reactant species M_a,M_b etc.and the product species M_l,M_m etc. are related by the general reaction whose stoichiometry is...
  9. R

    Equilibrium and displacement of a Particle

    Homework Statement The springs AB and BC have stiffness k and an unstretched length of l. Determine the displacement d of the cord from the wall when a force F is applied to the cord. See Picture attached. Given: l = 3 m k = 600 N/m F = 200 N Homework Equations Fspring= ks s=...
  10. shounakbhatta

    Hydrostatic equilibrium of a cylindrical area

    Hello, Consider a cylindrical region (length dr, end area dA) at a distance r from the center of the sun Density =ρ(r) Volume = Length x area = dr.dA (How is the formula for volume of a cylinder works here?) Mass= Density x Volume = ρ(r).dr.dA Now, computing F(grav) =...
  11. O

    Heat loss and thermal equilibrium of underground aquifer

    Homework Statement I am working on a project where I have to design and size an aquifer. There are two which either store hot or cold water for 6 months which is then pumped up to be used in either the summer or winter. The aquifer is going to be 80 meters under the ground. The rest is...
  12. G

    Solve Equilibrium Problem with Ammonium Phosphate

    Problem: I've been working on my assignment and the purpose of it is to determine the concentration of a contaminant present in a sample of water. I've discovered the contaminant is ammonium phosphate with the levels of each being 200% higher than normal water. I obtained these results using...
  13. R

    Rotational Equilibrium Homework Help

    Homework Statement Answers were told to us to be F = 2.91 N Ft1 = 13.32 N Ft2 = 3.36 N Homework Equations Fx = Ft2 cos(θ) - F = 0 Fy = Ft2 sin(θ) + Ft1 - Fg = 0 Torque equation -FgDg - Ft2D1x cos(θ) + Ft2D1y sin(θ) = 0 The Attempt at a Solution I plugged in all of the information i had...
  14. Astrum

    Static Equilibrium and D'Alembert's Principle

    Virtual work principle states: δW = \sum^{N}_{i=1}\vec{F}_{i}\centerdot δ\vec{r}_{i} And from this, we can see that if a system is to be in equilibrium we have δW = (\sum^{N}_{i=1}\vec{F}_{1} \centerdot \frac{\partial \vec{r}_{1}}{\partial q_{1}})δq_{1} + \cdots = 0 Where did q come...
  15. S

    Three forces - in equilibrium or not?

    Three forces -- in equilibrium or not? Hi. I am new to physics and need some help on this question asap. Did I get it right or is it wrong? Correct me if I am wrong. Thank you.
  16. S

    Static equilibrium - girl on diving board

    Homework Statement A diving board of length L is supported at a point a distance x from the end, and a diver weighing w1 stands at the free end (Figure 1) . The diving board is of uniform cross section and weighs w2. (Figure 1) Find the force at the support point. Find the force at the end...
  17. W

    Static Equilibrium Velocity

    1. What occurs during static equilibrium? 3. The net force and net torque on the object is zero. The acceleration of the object is zero too. Would velocity of the object also be zero? Or no because it has constant velocity?
  18. S

    Equilibrium of systems in acccelerating frame

    I've drawn the following FBD (using D'alembert prinicple) [The N in my drawing is the F_A stated in the question] ---------------- Assuming my FBD has nothing wrong, am I right to say that I am free to choose my torque equation about ANY POINT? somehow my solutions vary depending on my point...
  19. Y

    What is the Equilibrium of a Uniform Rod with Unknown Weight?

    Homework Statement A uniform, 263-N rod that is 2.20m long carries a 225-N weight at its right end and an unknown weight W toward the left end (see attached figure). When W is placed 55.6-cm from the left end of the rod, the system just balances horizontally when the fulcrum is located...
  20. H

    Relation between gibbs free energy and equilibrium constant

    I am familiar with the equation ΔG=ΔG°+RT ln(Q).But I can't derive it.We have to use the equation to derive nernst equation. So please help.
  21. M

    What is the relationship between particle velocity and sound waves in air?

    I have an air molecule moving because of a sound wave. f of sound wave = 500 Hz wavelength of sound wave = 0.68 m How fast is the air molecule moving in its equilibrium position? Is it in equilibrium at V max? Would this be where the position = 0?
  22. J

    Find Amplitude and Equilibrium in Simple Harmonic Motion

    Homework Statement A 0.241-kg particle undergoes simple harmonic motion along the horizontal x-axis between the points x1 = -0.349 m and x2 = 0.419 m. The period of oscillation is 0.511 s. Find the frequency, f, the equilibrium position, xeq, the amplitude, A. Homework Equations The...
  23. M

    Simple harmonic motion/static equilibrium -spring problem, mass given

    Homework Statement A 0.500 kg mass is suspended from a spring and set into oscillatory motion. A motion detector is used to record the motion, and it is found that its velocity function is given by Vx(t) What are: a. the period of the motion; b. the amplitude; c. the maximum acceleration...
  24. G

    Finding Equilibrium in a 3D System of Forces

    Homework Statement See attachment Homework Equations Let u be the angle between AC and AO and v the angle between BE and BD. Ta is the tension at point A and Tb is the tension at point B. The Attempt at a Solution Tried starting with the OAB body and got: -mg + Ta sin(u) + Tb...
  25. N

    Finding the equilibrium points of a differential equation

  26. R

    Finding the distance between 2 charges in electric equilibrium.

    Homework Statement Charge A and charge B are 2.2m apart.Charge A is 1.0C, and charge B is 2.0c. Charge C, which is 2.0C, is located between them and is in electrostatic equilibrium. How far from charge A is charge C. Homework Equations E = KcQ1Q2/r^2-------Electric force Formula where E...
  27. H

    The concept of rotational equilibrium

    Here is a text from my Physics Book : The net external torque on the object about any axis must be zero for it to be in rotational equilibrium. I divide the torques into two categories, anticlockwise and clockwise. (This approach works fine for 2-D objects but will it work for 3-D objects...
  28. M

    Tension & Torque, Static Equilibrium

    Homework Statement Homework Equations Ʃτ = 0 τ = rFsinθ The Attempt at a Solution I'm not even really sure where to start with this. My first thought was that it's not moving, so presumably the forces sum to 0. I also thought of treating the point where the net is exerting...
  29. S

    Torque and Equilibrium of a Rod

    Homework Statement Here's a diagram of a rod that's free to pivot about the point indicated. Is it possible to make the right end of the rod push down, by pulling on the left end of the rod? If so, show on the diagram the direction that you would pull on the left end of the rod, and explain...
  30. A

    How Do You Calculate Tension in a Hanging Mirror?

    Homework Statement Diagram 4 shows a 2 kg mirror hung on a wall using strings of the same length . The mirror is in equilibrium state. a) On Diagram 4 , label the force that act on the mirror . b) Calculate the tension of the string , T that act on the mirror . c) Suggest a modification to...
  31. P

    Quick Static Equilibrium Questions

    Homework Statement A horizontal beam of weight W is supported by a hinge and cable as shown. The force exerted on the beam by the hinge has a vertical component that must be: Answer is nonzero and up. The pull P is just sufficient to keep the 14-N block and the weightless pulleys in...
  32. O

    Ideal gas-thermodynamics, thermal equilibrium

    Homework Statement Two ideal gases are separated by a partition which does not allow molecules to pass from one volume to the other. Gas 1 has: N1, V1, T1, Cv1 for the number of molecules, volume it occupies, temperature in kelvin, and specific heat per molecule at constant volume...
  33. W

    Equilibrium bond lengths for excited molecules

    When making the Morse Potential graphs of diatomic molecules going through a transition, the excited state sometimes has a different equilibrium bond length. A visual example is here: http://en.wikipedia.org/wiki/File:Franck-Condon-diagram.png I was wondering how the average bond length of...
  34. L

    Static Equilibrium and a wheel

    Homework Statement what magnitude of force applied horizontally at the axle of the wheel is necessary to wheel over an obstacle of height h = 0.108 m? The wheel's radius is r = 0.698 m and its mass is m = 1.71 kg. Homework Equations I know that in order to have a static equilibrium we...
  35. K

    Equilibrium - A rod influenced by multiple rope tensions

    equilibrium -- A rod influenced by multiple rope tensions Homework Statement Smooth and identical rod has a weight of P. The rod seems to be in equilibrium with X and Y which has a weight of P. What can be the weight of X according to the values below?(ip means rope) P , 6P or 9PHomework...
  36. C

    Statics: Rigid Body Equilibrium

    Hello, I was wondering if someone could explain part of the solution to this problem for me. http://img706.imageshack.us/img706/5517/disksproblem.png To the right is the Free Body Diagram of Disk E, and I can draw the forces on there well enough. But I really do not understand how they...
  37. jaumzaum

    Liquid-Vapor Equilibrium and Vapor Pressure

    I'm studying vapor pressure and I'm having trouble to understand some concepts. Vapor pressure depends only on the temperature of the liquid in question right? For example, if we have a container with water at 30° C, it doesn't matter the experiment, would it ALWAYS be a vapor phase with...
  38. H

    Equilibrium, Torque and Friction (hard)

    Homework Statement A uniform solid cube, of edge 1m and weight 200N, rests on a rough horizontal plane. A light rod AB of length 1.2m is smoothly hinged at A to a point of the plane and B is in contact with a smooth face of the cube. The rod lies in a vertical plane perpendicular to...
  39. T

    Chemical Equilibrium Question

    Hi, I have simple question N2+3H2 = 2NH3 + heat How would the equilibrium position be affected if ammonia is removed from the vessel?, shouldn't it move to the left to produce more reactants and replace the ammonia? why does it move to the right?, because that's what my texbook says.
  40. F

    Find equilibrium points given 2 differential equation

    Homework Statement \dot{x} = -pxy + qx, \dot{y} = rxy - sy where p,q,r and s are positive constants (p does not equal r) Question is : Determine all the equilibrium points for the system of differential equations given above, expressing your answers in terms of p,q,r and s The...
  41. C

    Concentration of water vs. equilibrium

    Hi, I understand from calculation that the molar concentration of Pure water is 55.5 moles/Liter Then how come in equilibrium reactions when calculation the dissociation constant, we say that the concentration of water is 1 Molar? This seems like a huge difference to me? What is it I need...
  42. D

    Fermi Level of Electrons and Holes in Equilibrium and Non-Equilibrium

    Hi all, Why do the fermi level for electrons and holes coincide in equilibrium condition and why they separate as quasi fermi levels in non equilibrium situation?
  43. M

    Derivation for Time to Max Radioactivity Transient Equilibrium

    Hi, I'm having a bit of difficulty deriving the time to max activity for the case of transient equilibrium for a parent-daughter. This is where I want to get to , tm = (1 / (λ1-λ2)) * 1n(λ1/λ2) I believe there is an alternative equation for tm as well expressed in terms of half-life...
  44. R

    Equilibrium solutions in double well potential duffing oscillator

    Homework Statement I am trying to show that for a duffing oscillator described by x''+2g x'+ax+bx^3=0 with a<0, b>0 the equilibria at x=+- \sqrt{-a/b} are stable Homework Equations I used coupled equations, and the characteristic equation of a linear system The Attempt at a Solution...
  45. C

    Equilibrium and Minimum Force Requirements in a Frictionless Environment

    Hello physics whizzes. How much force is required to raise an item weighing 5,000kg to a height of 50 meters in a frictionless environment? It seems that all you would do is F = MA = (5000) (9.80665) = 49,033.25 Newtons, and that the height is irrelevant assuming that the gravity stays...
  46. G

    Calculation of No. of micro states (in equilibrium)

    Homework Statement Hello, I am required to determine the total number of micro states of a system in equilibrium within a certain value, 1/σ. The number of micro states for this system is given by, \Omega...
  47. T

    Equilibrium Constant Table Method

    Hi, I just want someone to explain this table to me please, I am totally confused especially with the Change(mol). Question below:
  48. S

    Equilibrium concentration of majority and minority carriers

    Homework Statement Give the equilibrium concentration of majority and minority carriers and resistivity for Silicon which is doped with 3x10^{15} boron atoms/cm^{3} at 27°C. Homework Equations n_{o} = \frac{N_{d}-N_{a}}{2}+\sqrt{(\frac{N_{d}-N_{a}}{2})^{2}+(n_{i})^{2}} p_{o} =...
  49. G

    Equilibrium state proof with lagrange

    Hello, I have been trying to follow the start of these lecture notes I found online and I have having trouble understanding what is happening between two steps. The notes I am looking at are located: http://pillowlab.cps.utexas.edu/teaching/CompNeuro10/slides/slides16_EntropyMethods.pdf...
  50. C

    Common temperature for thermal equilibrium

    Homework Statement One mole of copper at a uniform temp. of 0 Celsius is placed in thermal contact with a second mole of copper which, initially, is at a uniform temperature of 100 Celsius. The pressure in the system is maintained at 1 atm. The two moles of copper are thermally insulated from...
Back
Top